diff --git a/AGENTS.md b/AGENTS.md
index 50f86b17..e8eed03d 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -254,7 +254,7 @@ The API server is a Fastify app with a global `/api` prefix (`main.ts` excludes
 - **Redis** backs caching, the BullMQ queues, the WebSocket Socket.IO adapter, and collaboration sync.
 
 ### The two AI subsystems (the main fork additions)
-1. **Embedded MCP server** (`integrations/mcp/` + `packages/mcp`). The standalone `@docmost/mcp` server (38 agent-native tools: per-block patch/insert/delete by id, scripted `(doc)=>doc` transforms with dry-run diff, table editing, version diff/restore, comments, images, shares) is bundled and served over HTTP at `/mcp`. It writes through Docmost's real-time-collaboration layer so concurrent human edits aren't clobbered. Each request authenticates **per-user** via the `Authorization` header — either HTTP Basic (`base64(email:password)`, the user's own Docmost login, validated through `AuthService`) or a Bearer access JWT (the user's `authToken`) — and the session acts under that user's permissions. `MCP_DOCMOST_EMAIL` / `MCP_DOCMOST_PASSWORD` are an **optional service-account fallback**, used only when a request carries neither Basic nor Bearer credentials (back-compat for CI/scripts). An admin enables MCP with a workspace toggle (Workspace settings → AI). Optionally protected by a shared `MCP_TOKEN`: when set, every `/mcp` request must carry a matching `X-MCP-Token` header (its own header, separate from `Authorization`, which now carries the per-user Basic/Bearer credentials). Note: this changed from the older `Authorization: Bearer <MCP_TOKEN>` scheme — see `.env.example` and the CHANGELOG Breaking Changes entry.
+1. **Embedded MCP server** (`integrations/mcp/` + `packages/mcp`). The standalone `@docmost/mcp` server (39 agent-native tools: per-block patch/insert/delete by id, scripted `(doc)=>doc` transforms with dry-run diff, table editing, version diff/restore, comments, images, shares) is bundled and served over HTTP at `/mcp`. It writes through Docmost's real-time-collaboration layer so concurrent human edits aren't clobbered. Each request authenticates **per-user** via the `Authorization` header — either HTTP Basic (`base64(email:password)`, the user's own Docmost login, validated through `AuthService`) or a Bearer access JWT (the user's `authToken`) — and the session acts under that user's permissions. `MCP_DOCMOST_EMAIL` / `MCP_DOCMOST_PASSWORD` are an **optional service-account fallback**, used only when a request carries neither Basic nor Bearer credentials (back-compat for CI/scripts). An admin enables MCP with a workspace toggle (Workspace settings → AI). Optionally protected by a shared `MCP_TOKEN`: when set, every `/mcp` request must carry a matching `X-MCP-Token` header (its own header, separate from `Authorization`, which now carries the per-user Basic/Bearer credentials). Note: this changed from the older `Authorization: Bearer <MCP_TOKEN>` scheme — see `.env.example` and the CHANGELOG Breaking Changes entry.
 2. **AI agent chat** (`core/ai-chat/` server + `apps/client/src/features/ai-chat/` client). A built-in agent over the wiki using the Vercel **AI SDK** (`ai`, `@ai-sdk/*`) against any OpenAI-compatible provider configured per workspace (`integrations/ai/` — credentials encrypted at rest via `integrations/crypto`, stored in `ai_provider_credentials`). Key pieces:
    - `core/ai-chat/tools/` — the agent's ~40 read+write tools. Every tool runs under the **calling user's** CASL permissions via a per-user loopback access token (`docmost-client.loader.ts`), so the agent can never exceed what the user could do. Only **reversible** operations are exposed (page history + trash; no permanent delete). Agent edits get an "AI agent" provenance badge in page history (`20260616T130000-agent-provenance` migration).
    - `core/ai-chat/embedding/` — RAG indexer + a BullMQ consumer on `AI_QUEUE` that embeds pages into `page_embeddings` (vector search), complementing Postgres full-text search. Pages are (re)indexed on edit; `AI_EMBEDDING_TIMEOUT_MS` bounds a hung embeddings endpoint.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a46c61b8..cb79f364 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   `AI_AGENT_ROLES_CATALOG_URL` env var — an `http(s)://` base URL to the
   catalog's raw files; the image ships a per-branch default baked in CI, and it
   can be overridden at runtime via the env var (see `.env.example`). (#222)
+- **Author footnotes inline from an agent, and deterministic server-side footnote
+  canonicalization on every non-editor write path.** A new MCP `insert_footnote`
+  tool places a footnote at a body anchor by content only — the agent supplies
+  WHERE (anchor text) and WHAT (markdown); the number and the bottom
+  `footnotesList` are derived server-side, so an agent can never assign a number,
+  edit the list, or desync, and a same-content note reuses one definition. Under
+  the hood, the editor's footnote-integrity invariant (one trailing list,
+  numbering by first reference, no orphans/duplicates, no raw `[^id]`) is now
+  enforced as a pure `canonicalizeFootnotes(doc)` on the FULL-document write paths
+  that bypass the editor's plugins: server markdown/HTML import, `PageService`
+  create and full-document (`replace`) updates, the client markdown paste, and the
+  MCP markdown page-import / `update_page` (markdown) / `update_page_json` /
+  `docmost_transform` / `insert_footnote` / `copy_page_content` paths. It is
+  idempotent (a no-op once canonical) and is deliberately NOT applied to
+  append/prepend fragments, nor to COMMENT bodies — a comment may legitimately
+  contain a standalone footnote definition, which canonicalization would drop.
+  (#228)
 
 ### Fixed
 
diff --git a/README.md b/README.md
index cbbbdcab..8fd95cf5 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,7 @@ The goal of the fork is a **100% open, AGPL-only build with no Enterprise-Editio
 | --- | --- |
 | **EE code removed** | Stripped all client and server Enterprise-Edition code; ships as a clean community/AGPL build with no license checks. |
 | **Comment resolution** | Re-implemented from scratch as a community feature (resolve / re-open with Open/Resolved tabs). No EE code reused, available to anyone who can comment. |
-| **Embedded MCP server** | A community MCP server (`@docmost/mcp`, 38 tools) is served over HTTP at `/mcp` — no enterprise license required. Replaces the removed license-gated EE MCP. |
+| **Embedded MCP server** | A community MCP server (`@docmost/mcp`, 39 tools) is served over HTTP at `/mcp` — no enterprise license required. Replaces the removed license-gated EE MCP. |
 | **AI agent chat** | Built-in AI agent chat over your wiki, written from scratch as a community feature — no enterprise license. The agent reads and edits pages on your behalf (scoped to your permissions), with full-text + vector (RAG) search and optional web access via external MCP servers. |
 | **Rebranding** | App logo / name changed from *Docmost* to *Gitmost*. |
 | **Compact page tree** | Default page-tree indentation reduced from 16px to 8px per nesting level. |
@@ -44,7 +44,7 @@ The goal of the fork is a **100% open, AGPL-only build with no Enterprise-Editio
 ### Embedded MCP server
 
 Gitmost has **our own MCP server** — [docmost-mcp](https://github.com/vvzvlad/docmost-mcp),
-which we wrote — **built directly into the app** and served at `/mcp`. It exposes **38
+which we wrote — **built directly into the app** and served at `/mcp`. It exposes **39
 agent-native tools**: surgical per-block edits (patch / insert / delete by id),
 structure-preserving find/replace, scripted `(doc) => doc` transforms with a dry-run diff,
 structured table editing, version history with diff / restore, comments, images and share
@@ -60,7 +60,7 @@ every little fix. And it needs no enterprise license.
 | | **Gitmost `/mcp` (our docmost-mcp)** | Docmost's built-in MCP |
 | --- | :---: | :---: |
 | **Enterprise license** | Not required | Required |
-| **Tools** | 38, agent-native | Coarse (read Markdown, page CRUD, replace whole page) |
+| **Tools** | 39, agent-native | Coarse (read Markdown, page CRUD, replace whole page) |
 | **Per-block edits / find-replace / scripted transforms** | ✅ | — |
 | **Structured table editing, version diff / restore** | ✅ | — |
 | **Comments, images, share links** | ✅ | — |
diff --git a/README.ru.md b/README.ru.md
index 132ba442..ca980d31 100644
--- a/README.ru.md
+++ b/README.ru.md
@@ -33,7 +33,7 @@
 | --- | --- |
 | **Удалён EE-код** | Вырезан весь код Enterprise-редакции на клиенте и сервере; это чистая community/AGPL-сборка без лицензионных проверок. |
 | **Резолв комментариев** | Переписан с нуля как community-функция (резолв / переоткрытие с вкладками «Открытые» / «Решённые»). EE-код не используется, доступно любому, кто может комментировать. |
-| **Встроенный MCP-сервер** | Community MCP-сервер (`@docmost/mcp`, 38 инструментов) отдаётся по HTTP на `/mcp` — без enterprise-лицензии. Заменяет удалённый лицензируемый EE MCP. |
+| **Встроенный MCP-сервер** | Community MCP-сервер (`@docmost/mcp`, 39 инструментов) отдаётся по HTTP на `/mcp` — без enterprise-лицензии. Заменяет удалённый лицензируемый EE MCP. |
 | **Чат с AI-агентом** | Встроенный чат с AI-агентом по содержимому вики, написанный с нуля как community-функция — без enterprise-лицензии. Агент читает и редактирует страницы от вашего имени (в рамках ваших прав), с полнотекстовым + векторным (RAG) поиском и опциональным доступом в интернет через внешние MCP-серверы. |
 | **Ребрендинг** | Логотип / название приложения изменены с *Docmost* на *Gitmost*. |
 | **Компактное дерево страниц** | Отступ дерева страниц по умолчанию уменьшен с 16px до 8px на уровень вложенности. |
@@ -44,7 +44,7 @@
 
 В Gitmost есть **наш собственный MCP-сервер** — [docmost-mcp](https://github.com/vvzvlad/docmost-mcp),
 который мы написали сами, — **встроенный прямо в приложение** и доступный на `/mcp`. Он даёт
-**38 agent-native инструментов**: точечное редактирование по блокам (patch / insert / delete
+**39 agent-native инструментов**: точечное редактирование по блокам (patch / insert / delete
 по id), find/replace с сохранением структуры, скриптовые трансформации `(doc) => doc` с
 предпросмотром диффа, структурное редактирование таблиц, история версий с диффом /
 восстановлением, комментарии, изображения и ссылки на шаринг — всё применяется через слой
@@ -60,7 +60,7 @@ real-time-коллаборации Docmost, поэтому запись нико
 | | **`/mcp` в Gitmost (наш docmost-mcp)** | Родной MCP у Docmost |
 | --- | :---: | :---: |
 | **Enterprise-лицензия** | Не нужна | Нужна |
-| **Инструменты** | 38, agent-native | Примитивные (Markdown, CRUD страниц, замена целиком) |
+| **Инструменты** | 39, agent-native | Примитивные (Markdown, CRUD страниц, замена целиком) |
 | **Правки по блокам / find-replace / скриптовые трансформации** | ✅ | — |
 | **Структурное редактирование таблиц, дифф / восстановление версий** | ✅ | — |
 | **Комментарии, изображения, ссылки на шаринг** | ✅ | — |
diff --git a/apps/client/src/features/editor/extensions/markdown-clipboard.canonicalize.test.ts b/apps/client/src/features/editor/extensions/markdown-clipboard.canonicalize.test.ts
new file mode 100644
index 00000000..e4d83288
--- /dev/null
+++ b/apps/client/src/features/editor/extensions/markdown-clipboard.canonicalize.test.ts
@@ -0,0 +1,168 @@
+import { describe, it, expect } from "vitest";
+import { Editor } from "@tiptap/core";
+import { Document } from "@tiptap/extension-document";
+import { Paragraph } from "@tiptap/extension-paragraph";
+import { Text } from "@tiptap/extension-text";
+import { Node as PMNode, Fragment, Slice } from "@tiptap/pm/model";
+import {
+  FootnoteReference,
+  FootnotesList,
+  FootnoteDefinition,
+  FOOTNOTE_REFERENCE_NAME,
+  FOOTNOTE_DEFINITION_NAME,
+  FOOTNOTES_LIST_NAME,
+} from "@docmost/editor-ext";
+import { canonicalizePastedFootnotes } from "./markdown-clipboard";
+
+/**
+ * A markdown paste builds its ProseMirror fragment via DOM -> parseSlice and is
+ * applied with a manual transaction (handlePaste returns true), so it bypasses
+ * the editor's footnoteSyncPlugin — which never reorders an existing list. These
+ * tests pin canonicalizePastedFootnotes, the focused hook that makes a pasted
+ * out-of-order markdown footnote block come out canonical (issue #228).
+ */
+
+const extensions = [
+  Document,
+  Paragraph,
+  Text,
+  FootnoteReference,
+  FootnotesList,
+  FootnoteDefinition,
+];
+
+function makeSchema() {
+  const editor = new Editor({ extensions, content: { type: "doc", content: [] } });
+  const { schema } = editor;
+  return { editor, schema };
+}
+
+/** List footnote def ids of the (single) footnotesList in a slice, in order. */
+function listIds(slice: Slice): string[] {
+  const out: string[] = [];
+  slice.content.forEach((node: PMNode) => {
+    if (node.type.name === FOOTNOTES_LIST_NAME) {
+      node.content.forEach((def: PMNode) => {
+        if (def.type.name === FOOTNOTE_DEFINITION_NAME) out.push(def.attrs.id);
+      });
+    }
+  });
+  return out;
+}
+
+function hasList(slice: Slice): boolean {
+  let found = false;
+  slice.content.forEach((n: PMNode) => {
+    if (n.type.name === FOOTNOTES_LIST_NAME) found = true;
+  });
+  return found;
+}
+
+describe("canonicalizePastedFootnotes", () => {
+  it("reorders a pasted block to reference order, dedups reuse, drops orphans", () => {
+    const { editor, schema } = makeSchema();
+    // Body references c, a, b (and again a => reuse); definitions a, b, c, z
+    // (z is an orphan) — the exact shape a markdown paste produces.
+    const slice = new Slice(
+      Fragment.fromArray([
+        schema.nodes.paragraph.create(null, [
+          schema.text("body "),
+          schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: "c" }),
+          schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: "a" }),
+          schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: "b" }),
+          schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: "a" }),
+        ]),
+        schema.nodes[FOOTNOTES_LIST_NAME].create(null, [
+          schema.nodes[FOOTNOTE_DEFINITION_NAME].create({ id: "a" }, [
+            schema.nodes.paragraph.create(null, [schema.text("note A")]),
+          ]),
+          schema.nodes[FOOTNOTE_DEFINITION_NAME].create({ id: "b" }, [
+            schema.nodes.paragraph.create(null, [schema.text("note B")]),
+          ]),
+          schema.nodes[FOOTNOTE_DEFINITION_NAME].create({ id: "c" }, [
+            schema.nodes.paragraph.create(null, [schema.text("note C")]),
+          ]),
+          schema.nodes[FOOTNOTE_DEFINITION_NAME].create({ id: "z" }, [
+            schema.nodes.paragraph.create(null, [schema.text("orphan")]),
+          ]),
+        ]),
+      ]),
+      0,
+      0,
+    );
+
+    const out = canonicalizePastedFootnotes(slice, schema);
+    // Reference order, orphan z dropped, reused a appears once.
+    expect(listIds(out)).toEqual(["c", "a", "b"]);
+    editor.destroy();
+  });
+
+  it("leaves a reference-ONLY paste untouched (no synthesized definitions)", () => {
+    // A paste that reuses an id defined in the TARGET doc must NOT gain a
+    // synthesized empty definition here — it carries no footnotesList of its own.
+    const { editor, schema } = makeSchema();
+    const slice = new Slice(
+      Fragment.from(
+        schema.nodes.paragraph.create(null, [
+          schema.text("see "),
+          schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: "a" }),
+        ]),
+      ),
+      0,
+      0,
+    );
+    const out = canonicalizePastedFootnotes(slice, schema);
+    expect(hasList(out)).toBe(false);
+    expect(out).toBe(slice); // returned unchanged (same reference)
+    editor.destroy();
+  });
+
+  it("leaves a definitions-ONLY paste untouched (no references -> no empty paste)", () => {
+    // A whole-block paste of ONLY definitions (a footnotesList with no matching
+    // footnoteReference anywhere in the selection). Canonicalizing it would strip
+    // the reference-less list -> an EMPTY paste, losing the pasted text. The hook
+    // must leave such a block untouched.
+    const { editor, schema } = makeSchema();
+    const slice = new Slice(
+      Fragment.fromArray([
+        schema.nodes[FOOTNOTES_LIST_NAME].create(null, [
+          schema.nodes[FOOTNOTE_DEFINITION_NAME].create({ id: "a" }, [
+            schema.nodes.paragraph.create(null, [schema.text("note A")]),
+          ]),
+          schema.nodes[FOOTNOTE_DEFINITION_NAME].create({ id: "b" }, [
+            schema.nodes.paragraph.create(null, [schema.text("note B")]),
+          ]),
+        ]),
+      ]),
+      0,
+      0,
+    );
+    const out = canonicalizePastedFootnotes(slice, schema);
+    expect(out).toBe(slice); // returned unchanged (same reference, content kept)
+    expect(listIds(out)).toEqual(["a", "b"]);
+    editor.destroy();
+  });
+
+  it("leaves an open (partial) slice untouched even if it carries a list", () => {
+    // An open slice (openStart/openEnd > 0) is a partial selection, not a
+    // standalone block, so it is returned as-is BEFORE any footnote handling.
+    const { editor, schema } = makeSchema();
+    const slice = new Slice(
+      Fragment.fromArray([
+        schema.nodes.paragraph.create(null, [
+          schema.nodes[FOOTNOTE_REFERENCE_NAME].create({ id: "a" }),
+        ]),
+        schema.nodes[FOOTNOTES_LIST_NAME].create(null, [
+          schema.nodes[FOOTNOTE_DEFINITION_NAME].create({ id: "a" }, [
+            schema.nodes.paragraph.create(null, [schema.text("A")]),
+          ]),
+        ]),
+      ]),
+      1,
+      1,
+    );
+    const out = canonicalizePastedFootnotes(slice, schema);
+    expect(out).toBe(slice);
+    editor.destroy();
+  });
+});
diff --git a/apps/client/src/features/editor/extensions/markdown-clipboard.ts b/apps/client/src/features/editor/extensions/markdown-clipboard.ts
index bebb567a..c8e36a1b 100644
--- a/apps/client/src/features/editor/extensions/markdown-clipboard.ts
+++ b/apps/client/src/features/editor/extensions/markdown-clipboard.ts
@@ -3,7 +3,14 @@ import { Extension } from "@tiptap/core";
 import { Plugin, PluginKey, TextSelection } from "@tiptap/pm/state";
 import { DOMParser, DOMSerializer, Fragment, Slice } from "@tiptap/pm/model";
 import { find } from "linkifyjs";
-import { markdownToHtml, htmlToMarkdown } from "@docmost/editor-ext";
+import {
+  markdownToHtml,
+  htmlToMarkdown,
+  canonicalizeFootnotes,
+  FOOTNOTES_LIST_NAME,
+  FOOTNOTE_REFERENCE_NAME,
+} from "@docmost/editor-ext";
+import type { Schema } from "@tiptap/pm/model";
 
 export const MarkdownClipboard = Extension.create({
   name: "markdownClipboard",
@@ -83,12 +90,25 @@ export const MarkdownClipboard = Extension.create({
             const body = elementFromString(parsed);
             normalizeTableColumnWidths(body);
 
-            const contentNodes = DOMParser.fromSchema(
+            const parsedSlice = DOMParser.fromSchema(
               this.editor.schema,
             ).parseSlice(body, {
               preserveWhitespace: true,
             });
 
+            // A markdown paste builds its ProseMirror fragment directly (DOM ->
+            // parseSlice), bypassing the editor's footnoteSyncPlugin, which never
+            // reorders an existing list. So a pasted markdown block whose footnote
+            // definitions are out of order (or contains orphan defs) would be
+            // stored out of order. Canonicalize the self-contained pasted block so
+            // its footnotes come out reference-ordered, deduped and orphan-free
+            // (issue #228). See canonicalizePastedFootnotes for why this is scoped
+            // to whole-block pastes that carry their own footnotesList.
+            const contentNodes = canonicalizePastedFootnotes(
+              parsedSlice,
+              this.editor.schema,
+            );
+
             tr.replaceRange(from, to, contentNodes);
             const insertEnd = tr.mapping.map(from, 1);
             tr.setSelection(TextSelection.near(tr.doc.resolve(Math.max(from, insertEnd - 2)), -1));
@@ -133,6 +153,54 @@ export const MarkdownClipboard = Extension.create({
   },
 });
 
+/**
+ * Reorder/dedup the footnotes of a SELF-CONTAINED pasted markdown block to the
+ * canonical invariant (the live footnoteSyncPlugin never reorders an existing
+ * list, so an out-of-order pasted block would otherwise persist out of order).
+ *
+ * Scoped deliberately to whole-block pastes (openStart/openEnd === 0) that carry
+ * their OWN footnotesList: canonicalizeFootnotes would synthesize empty
+ * definitions for any reference lacking a definition, which is correct for a
+ * standalone block but would be wrong for a reference-only paste that REUSES a
+ * footnote already defined in the target document — so those are left untouched
+ * for the paste/sync plugins to merge. Residual: when the pasted block is merged
+ * into a doc that already has footnotes, ordering RELATIVE to the pre-existing
+ * footnotes is still governed by the sync plugin (which does not reorder).
+ *
+ * Also requires at least one footnoteReference in the selection: a definitions-ONLY
+ * paste (`[^a]: …` with no `[^a]` reference in the same block) has no references,
+ * so canonicalizeFootnotes would drop the whole list and the paste would come out
+ * EMPTY — losing the pasted text. Such a block is left as-is for the sync plugin.
+ */
+export function canonicalizePastedFootnotes(slice: Slice, schema: Schema): Slice {
+  if (slice.openStart !== 0 || slice.openEnd !== 0) return slice;
+
+  let hasFootnotesList = false;
+  let hasReference = false;
+  slice.content.forEach((node) => {
+    if (node.type.name === FOOTNOTES_LIST_NAME) hasFootnotesList = true;
+    // footnoteReference is an inline atom, never a top-level slice child here
+    // (this function early-returns for open slices, so children are whole
+    // blocks), so it is only reachable by descending.
+    node.descendants((child) => {
+      if (child.type.name === FOOTNOTE_REFERENCE_NAME) hasReference = true;
+    });
+  });
+  if (!hasFootnotesList) return slice;
+  // No reference anywhere -> a definitions-only paste; canonicalizing would strip
+  // the reference-less list (empty paste). Leave it untouched.
+  if (!hasReference) return slice;
+
+  const content = slice.content.toJSON();
+  if (!Array.isArray(content)) return slice;
+
+  const canonical = canonicalizeFootnotes({ type: "doc", content }) as {
+    content?: unknown[];
+  };
+  const fragment = Fragment.fromJSON(schema, canonical.content ?? []);
+  return new Slice(fragment, 0, 0);
+}
+
 function elementFromString(value) {
   // add a wrapper to preserve leading and trailing whitespace
   const wrappedValue = `<body>${value}</body>`;
diff --git a/apps/server/src/core/page/services/page.service.footnote-canonicalize.spec.ts b/apps/server/src/core/page/services/page.service.footnote-canonicalize.spec.ts
new file mode 100644
index 00000000..3d2dac75
--- /dev/null
+++ b/apps/server/src/core/page/services/page.service.footnote-canonicalize.spec.ts
@@ -0,0 +1,153 @@
+// Binding test for issue #228 must-fix #1 / test-coverage #12: footnote
+// canonicalization moved OUT of parseProsemirrorContent and is now applied only
+// on FULL-document writes (createPage, and updatePageContent with operation
+// 'replace'), NEVER on an append/prepend FRAGMENT.
+//
+// The Yjs encode / plain-text extract are stubbed (partial module mock keeps the
+// REAL canonicalizeFootnotes) and parseProsemirrorContent is spied to return the
+// raw fixture, so the test isolates the canonicalize BINDING from schema/Yjs.
+jest.mock('@docmost/editor-ext', () => {
+  const actual = jest.requireActual('@docmost/editor-ext');
+  return {
+    ...actual,
+    createYdocFromJson: jest.fn(() => Buffer.from([])),
+    jsonToText: jest.fn(() => ''),
+  };
+});
+
+import { PageService } from './page.service';
+
+const refNode = (id: string) => ({ type: 'footnoteReference', attrs: { id } });
+const defNode = (id: string, text: string) => ({
+  type: 'footnoteDefinition',
+  attrs: { id },
+  content: [{ type: 'paragraph', content: [{ type: 'text', text }] }],
+});
+const doc = (...content: any[]) => ({ type: 'doc', content });
+
+/** A full doc whose footnote definitions are OUT of reference order (b,a refs;
+ *  a,b defs) — canonicalization must reorder the definitions to [b, a]. */
+const outOfOrderFull = () =>
+  doc(
+    { type: 'paragraph', content: [{ type: 'text', text: 'x' }, refNode('b'), refNode('a')] },
+    { type: 'footnotesList', content: [defNode('a', 'A'), defNode('b', 'B')] },
+  );
+
+/** A definition-ONLY fragment (no references): canonicalizing it would drop the
+ *  whole footnotesList (referenceIds is empty) — i.e. LOSE the footnote. */
+const defOnlyFragment = () =>
+  doc({ type: 'footnotesList', content: [defNode('a', 'appended note')] });
+
+/** A reference-only fragment that REUSES an id defined elsewhere in the live
+ *  doc: canonicalizing it would synthesize a bogus empty footnotesList/def. */
+const refReuseFragment = () =>
+  doc({ type: 'paragraph', content: [{ type: 'text', text: 'more' }, refNode('a')] });
+
+function listDefIds(content: any): string[] {
+  const list = (content.content ?? []).find((n: any) => n.type === 'footnotesList');
+  return (list?.content ?? [])
+    .filter((n: any) => n.type === 'footnoteDefinition')
+    .map((n: any) => n.attrs?.id);
+}
+function hasFootnotesList(content: any): boolean {
+  return (content.content ?? []).some((n: any) => n.type === 'footnotesList');
+}
+
+describe('PageService footnote canonicalization binding (#228)', () => {
+  function makeService() {
+    let insertedContent: any = null;
+    let yjsPayload: any = null;
+
+    const pageRepo = {
+      insertPage: jest.fn(async (values: any) => {
+        insertedContent = values.content;
+        return { id: 'page-id', slugId: 'slug-id' };
+      }),
+    };
+    const generalQueue = { add: jest.fn().mockReturnValue({ catch: jest.fn() }) };
+    const collaborationGateway = {
+      handleYjsEvent: jest.fn(async (_evt: string, _name: string, payload: any) => {
+        yjsPayload = payload;
+      }),
+    };
+
+    const service = new PageService(
+      pageRepo as any,
+      {} as any, // pagePermissionRepo
+      {} as any, // attachmentRepo
+      {} as any, // db
+      {} as any, // storageService
+      {} as any, // attachmentQueue
+      {} as any, // aiQueue
+      generalQueue as any,
+      {} as any, // eventEmitter
+      collaborationGateway as any,
+      {} as any, // watcherService
+      {} as any, // transclusionService
+    );
+    // Isolate the canonicalize BINDING: return the raw fixture (a deep clone so
+    // canonicalize never mutates the caller's object) instead of running the
+    // real markdown/HTML/JSON parse + schema validation.
+    jest
+      .spyOn(service as any, 'parseProsemirrorContent')
+      .mockImplementation(async (content: any) => structuredClone(content));
+    jest.spyOn(service as any, 'nextPagePosition').mockResolvedValue('a0');
+
+    return { service, getInsertedContent: () => insertedContent, getYjsPayload: () => yjsPayload };
+  }
+
+  it('createPage (full write) canonicalizes footnotes into reference order', async () => {
+    const { service, getInsertedContent } = makeService();
+    await service.create('user-id', 'workspace-id', {
+      spaceId: 'space-id',
+      content: outOfOrderFull(),
+      format: 'json',
+    } as any);
+    // Definitions reordered to reference order [b, a].
+    expect(listDefIds(getInsertedContent())).toEqual(['b', 'a']);
+  });
+
+  it("updatePageContent operation 'replace' canonicalizes footnotes", async () => {
+    const { service, getYjsPayload } = makeService();
+    await service.updatePageContent(
+      'page-id',
+      outOfOrderFull(),
+      'replace' as any,
+      'json' as any,
+      { id: 'user-id' } as any,
+    );
+    expect(getYjsPayload().operation).toBe('replace');
+    expect(listDefIds(getYjsPayload().prosemirrorJson)).toEqual(['b', 'a']);
+  });
+
+  it("append of a definition-only fragment is NOT canonicalized (footnote preserved, not dropped)", async () => {
+    const { service, getYjsPayload } = makeService();
+    await service.updatePageContent(
+      'page-id',
+      defOnlyFragment(),
+      'append' as any,
+      'json' as any,
+      { id: 'user-id' } as any,
+    );
+    // Canonicalizing a reference-less fragment would DROP the whole list; the
+    // fragment must pass through untouched so the merge keeps the definition.
+    expect(getYjsPayload().operation).toBe('append');
+    expect(hasFootnotesList(getYjsPayload().prosemirrorJson)).toBe(true);
+    expect(listDefIds(getYjsPayload().prosemirrorJson)).toEqual(['a']);
+  });
+
+  it('prepend of a reference-reuse fragment is NOT canonicalized (no synthesized garbage list)', async () => {
+    const { service, getYjsPayload } = makeService();
+    await service.updatePageContent(
+      'page-id',
+      refReuseFragment(),
+      'prepend' as any,
+      'json' as any,
+      { id: 'user-id' } as any,
+    );
+    // Canonicalizing would synthesize a bogus empty footnotesList for the reused
+    // reference; the fragment must pass through with no list at all.
+    expect(getYjsPayload().operation).toBe('prepend');
+    expect(hasFootnotesList(getYjsPayload().prosemirrorJson)).toBe(false);
+  });
+});
diff --git a/apps/server/src/core/page/services/page.service.ts b/apps/server/src/core/page/services/page.service.ts
index aeb59eff..c6ee150d 100644
--- a/apps/server/src/core/page/services/page.service.ts
+++ b/apps/server/src/core/page/services/page.service.ts
@@ -52,7 +52,7 @@ import {
   INTERNAL_LINK_REGEX,
   extractPageSlugId,
 } from '../../../integrations/export/utils';
-import { markdownToHtml } from '@docmost/editor-ext';
+import { markdownToHtml, canonicalizeFootnotes } from '@docmost/editor-ext';
 import { WatcherService } from '../../watcher/watcher.service';
 import { sql } from 'kysely';
 import { TransclusionService } from '../transclusion/transclusion.service';
@@ -160,9 +160,14 @@ export class PageService {
     let ydoc = undefined;
 
     if (createPageDto?.content && createPageDto?.format) {
-      const prosemirrorJson = await this.parseProsemirrorContent(
-        createPageDto.content,
-        createPageDto.format,
+      // createPage always writes a FULL document, so canonicalize footnotes to
+      // the editor's invariant before persisting (issue #228). Pure + idempotent
+      // + shape-safe: a doc with no footnotes is returned unchanged.
+      const prosemirrorJson = canonicalizeFootnotes(
+        await this.parseProsemirrorContent(
+          createPageDto.content,
+          createPageDto.format,
+        ),
       );
 
       content = prosemirrorJson;
@@ -343,7 +348,17 @@ export class PageService {
     format: ContentFormat,
     user: User,
   ): Promise<void> {
-    const prosemirrorJson = await this.parseProsemirrorContent(content, format);
+    let prosemirrorJson = await this.parseProsemirrorContent(content, format);
+
+    // Canonicalize footnotes ONLY for a full-document write ('replace'). For an
+    // append/prepend FRAGMENT, canonicalizing is semantically wrong (it would
+    // drop a definition-only fragment's list, or synthesize a duplicate empty
+    // definition for a fragment reusing an existing id) — the fragment merges
+    // into the live doc where the editor's footnoteSyncPlugin keeps the invariant
+    // (issue #228, must-fix #1).
+    if (operation === 'replace') {
+      prosemirrorJson = canonicalizeFootnotes(prosemirrorJson);
+    }
 
     const documentName = `page.${pageId}`;
     await this.collaborationGateway.handleYjsEvent(
@@ -1301,6 +1316,24 @@ export class PageService {
       }
     }
 
+    // NOTE: footnote canonicalization is intentionally NOT done here. This
+    // method serves BOTH full writes (createPage / updatePageContent with
+    // operation 'replace') AND fragment writes (append / prepend). Canonicalizing
+    // a FRAGMENT is semantically wrong — e.g. a definition-only fragment has no
+    // references, so the canonicalizer would drop its whole footnotesList (lost
+    // footnotes), and a fragment reusing an existing id would synthesize an empty
+    // duplicate definition. The canonicalizer therefore runs only at the
+    // FULL-DOCUMENT callers (createPage, and updatePageContent for 'replace'),
+    // never on a fragment (issue #228, must-fix #1).
+    // (Future consolidation, architecture B: the import services persist via a
+    // different path; folding all of these into one "prepare JSON for persist"
+    // helper would centralize the canonicalize call — left as follow-up.)
+    //
+    // ENFORCEMENT RULE (#228): any NEW FULL-document persist path MUST call
+    // `canonicalizeFootnotes(json)` before writing (see createPage and
+    // updatePageContent 'replace'); append/prepend FRAGMENT writes MUST NOT (it
+    // would drop or duplicate footnotes — that is exactly why this is per-call-site
+    // rather than a single wrapper here).
     try {
       jsonToNode(prosemirrorJson);
     } catch (err) {
diff --git a/apps/server/src/integrations/import/services/file-import-task.service.footnote-canonicalize.spec.ts b/apps/server/src/integrations/import/services/file-import-task.service.footnote-canonicalize.spec.ts
new file mode 100644
index 00000000..08ecce15
--- /dev/null
+++ b/apps/server/src/integrations/import/services/file-import-task.service.footnote-canonicalize.spec.ts
@@ -0,0 +1,150 @@
+// Importing FileImportTaskService transitively loads import-formatter.ts, which
+// imports the ESM-only @sindresorhus/slugify package (not in jest's transform
+// allowlist). slugify is irrelevant to the path under test, so it is mocked out
+// to keep the module graph loadable under ts-jest (mirrors the import.service spec).
+jest.mock('@sindresorhus/slugify', () => ({
+  __esModule: true,
+  default: (input: string) => String(input),
+}));
+// import-attachment.service.ts (loaded transitively for DI typing) imports the
+// ESM-only `p-limit` / `image-dimensions`; neither is exercised on the path under
+// test, so stub them so the module graph loads under ts-jest.
+jest.mock('p-limit', () => ({
+  __esModule: true,
+  default: () => (fn: any) => fn(),
+}));
+jest.mock('image-dimensions', () => ({
+  __esModule: true,
+  imageDimensionsFromData: () => undefined,
+}));
+
+import { promises as fs } from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { FileImportTaskService } from './file-import-task.service';
+import { ImportService } from './import.service';
+
+/**
+ * Binding test for issue #228 / review #5: FileImportTaskService.processGenericImport
+ * is a NON-editor write path (markdownToHtml -> processHTML -> JSON, never runs
+ * footnoteSyncPlugin), so it canonicalizes footnotes before persisting. This pins
+ * that binding — the same one import.service has a spec for — which previously had
+ * NO spec at all.
+ *
+ * The markdown -> HTML -> ProseMirror conversion is REAL (a real ImportService,
+ * its createYdoc stubbed); the filesystem is a real temp dir with one .md file;
+ * the DB transaction is stubbed to capture the persisted page content.
+ */
+
+// Out-of-order references (c, a, b), a REUSED reference ([^a] twice), and an
+// ORPHAN definition ([^z], never referenced).
+const MARKDOWN = [
+  '# Title',
+  '',
+  'Body refs [^c] and [^a] and [^b] and again [^a].',
+  '',
+  '[^a]: note A',
+  '[^b]: note B',
+  '[^c]: note C',
+  '[^z]: orphan note',
+].join('\n');
+
+function footnoteListIds(content: any): string[] {
+  const list = (content?.content ?? []).find(
+    (n: any) => n.type === 'footnotesList',
+  );
+  return (list?.content ?? [])
+    .filter((n: any) => n.type === 'footnoteDefinition')
+    .map((n: any) => n.attrs?.id);
+}
+
+// A permissive chainable stub for the spaces lookup (selectFrom(...).select(...)
+// .where(...).executeTakeFirst()).
+function chainable(result: any): any {
+  const proxy: any = new Proxy(function () {}, {
+    get: (_t, prop) => {
+      if (prop === 'executeTakeFirst') return async () => result;
+      if (prop === 'execute') return async () => [];
+      return () => proxy;
+    },
+  });
+  return proxy;
+}
+
+describe('FileImportTaskService.processGenericImport — footnote canonicalization (#228)', () => {
+  it('orders footnotes by first reference, dedupes reuse, and drops orphans on zip import', async () => {
+    const extractDir = await fs.mkdtemp(path.join(os.tmpdir(), 'fit-canon-'));
+    await fs.writeFile(path.join(extractDir, 'note.md'), MARKDOWN, 'utf-8');
+
+    // Real ImportService for the html -> JSON conversion; stub the yjs encode.
+    const importService = new ImportService(
+      {} as any,
+      {} as any,
+      {} as any,
+      {} as any,
+    );
+    jest
+      .spyOn(importService as any, 'createYdoc')
+      .mockResolvedValue(Buffer.from([]) as any);
+
+    let captured: any = null;
+    const trx = {
+      insertInto: (table: string) => ({
+        values: (v: any) => {
+          if (table === 'pages') captured = v;
+          return { execute: async () => {} };
+        },
+      }),
+    };
+    const db: any = {
+      selectFrom: () => chainable({ slug: 'space-slug' }),
+      transaction: () => ({ execute: (fn: any) => fn(trx) }),
+    };
+
+    const importAttachmentService = {
+      processAttachments: async ({ html }: any) => html,
+    };
+    const backlinkRepo = { insertBacklink: jest.fn() };
+    const eventEmitter = { emit: jest.fn() };
+    const auditService = { logBatchWithContext: jest.fn() };
+
+    const pageService = { nextPagePosition: async () => 'a0' };
+
+    const service = new FileImportTaskService(
+      {} as any, // storageService
+      importService as any,
+      pageService as any,
+      backlinkRepo as any,
+      db,
+      importAttachmentService as any,
+      eventEmitter as any,
+      auditService as any,
+    );
+
+    const fileTask: any = {
+      id: 'task-1',
+      source: 'generic',
+      spaceId: 'space-1',
+      workspaceId: 'ws-1',
+      creatorId: 'user-1',
+    };
+
+    try {
+      await service.processGenericImport({ extractDir, fileTask });
+
+      expect(captured).toBeTruthy();
+      const content = captured.content;
+      // Reference order is c, a, b (NOT the markdown definition order a, b, c).
+      expect(footnoteListIds(content)).toEqual(['c', 'a', 'b']);
+      // Orphan [^z] dropped; reused [^a] collapses to one definition; one list.
+      expect(footnoteListIds(content)).not.toContain('z');
+      const lists = (content.content ?? []).filter(
+        (n: any) => n.type === 'footnotesList',
+      );
+      expect(lists).toHaveLength(1);
+      expect(footnoteListIds(content).filter((id) => id === 'a')).toHaveLength(1);
+    } finally {
+      await fs.rm(extractDir, { recursive: true, force: true });
+    }
+  });
+});
diff --git a/apps/server/src/integrations/import/services/file-import-task.service.ts b/apps/server/src/integrations/import/services/file-import-task.service.ts
index 218c75ca..5ec2fe8d 100644
--- a/apps/server/src/integrations/import/services/file-import-task.service.ts
+++ b/apps/server/src/integrations/import/services/file-import-task.service.ts
@@ -18,7 +18,7 @@ import { generateSlugId } from '../../../common/helpers';
 import { v7 } from 'uuid';
 import { generateJitteredKeyBetween } from 'fractional-indexing-jittered';
 import { FileTask, InsertablePage } from '@docmost/db/types/entity.types';
-import { markdownToHtml } from '@docmost/editor-ext';
+import { markdownToHtml, canonicalizeFootnotes } from '@docmost/editor-ext';
 import { getProsemirrorContent } from '../../../common/helpers/prosemirror/utils';
 import { formatImportHtml } from '../utils/import-formatter';
 import {
@@ -496,9 +496,19 @@ export class FileImportTaskService {
               await this.importService.processHTML(html),
             );
 
-            const { title, prosemirrorJson } =
+            const { title, prosemirrorJson: extractedJson } =
               this.importService.extractTitleAndRemoveHeading(pmState);
 
+            // Canonicalize footnote topology on this non-editor write path
+            // (markdownToHtml/processHTML never runs footnoteSyncPlugin), so a
+            // zip-imported page's footnotes are reference-ordered, deduped, and
+            // orphan-free like the editor's invariant (issue #228). Pure +
+            // idempotent + shape-safe; a footnote-free doc is unchanged.
+            // (Future consolidation, architecture B: like import.service, this
+            // path persists directly rather than via PageService — a shared
+            // "prepare JSON for persist" helper would centralize this call.)
+            const prosemirrorJson = canonicalizeFootnotes(extractedJson);
+
             const insertablePage: InsertablePage = {
               id: page.id,
               slugId: page.slugId,
diff --git a/apps/server/src/integrations/import/services/import.service.footnote-canonicalize.spec.ts b/apps/server/src/integrations/import/services/import.service.footnote-canonicalize.spec.ts
new file mode 100644
index 00000000..e53b17a1
--- /dev/null
+++ b/apps/server/src/integrations/import/services/import.service.footnote-canonicalize.spec.ts
@@ -0,0 +1,139 @@
+// Importing ImportService transitively loads import-formatter.ts, which imports
+// the ESM-only @sindresorhus/slugify package (not in jest's transform
+// allowlist). slugify is irrelevant to the path under test, so it is mocked out
+// to keep the module graph loadable under ts-jest.
+jest.mock('@sindresorhus/slugify', () => ({
+  __esModule: true,
+  default: (input: string) => String(input),
+}));
+
+import { ImportService } from './import.service';
+import { canonicalizeFootnotes } from '@docmost/editor-ext';
+
+/**
+ * Integration-ish test for the USER-FACING markdown import path
+ * (`ImportService.importPage`). It exercises the REAL markdown -> HTML -> JSON
+ * conversion and asserts that the stored page content has its footnotes
+ * canonicalized — the gap that issue #228 fixes: the import path builds
+ * ProseMirror JSON directly (never running the editor's footnoteSyncPlugin), so
+ * before this wiring the stored footnotes kept the markdown's physical
+ * definition order (out of order vs. references), retained orphan definitions,
+ * and did not collapse reused references.
+ *
+ * The DB/ydoc side-effects are stubbed: `getNewPagePosition` (DB query) and
+ * `createYdoc` (Yjs encode) are spied, and `pageRepo.insertPage` captures the
+ * persisted `content`. Everything between markdown and persistence is REAL.
+ */
+
+// Out-of-order references (c, a, b), a REUSED reference ([^a] twice -> one
+// footnote), and an ORPHAN definition ([^z], never referenced).
+const MARKDOWN = [
+  '# Title',
+  '',
+  'Body refs [^c] and [^a] and [^b] and again [^a].',
+  '',
+  '[^a]: note A',
+  '[^b]: note B',
+  '[^c]: note C',
+  '[^z]: orphan note',
+].join('\n');
+
+function makeFile(filename: string, contents: string) {
+  return {
+    filename,
+    toBuffer: async () => Buffer.from(contents),
+  } as any;
+}
+
+function makeService() {
+  let captured: any = null;
+  const pageRepo = {
+    insertPage: jest.fn(async (values: any) => {
+      captured = values;
+      return { id: 'page-id', slugId: 'slug-id' };
+    }),
+  };
+  const service = new ImportService(
+    pageRepo as any,
+    {} as any,
+    {} as any,
+    {} as any,
+  );
+  jest.spyOn(service as any, 'getNewPagePosition').mockResolvedValue('a0');
+  jest
+    .spyOn(service as any, 'createYdoc')
+    .mockResolvedValue(Buffer.from([]) as any);
+  return { service, pageRepo, getCaptured: () => captured };
+}
+
+/** List the footnote-definition ids of the (single) footnotesList, in order. */
+function footnoteListIds(content: any): string[] {
+  const list = (content.content ?? []).find(
+    (n: any) => n.type === 'footnotesList',
+  );
+  if (!list) return [];
+  return (list.content ?? [])
+    .filter((n: any) => n.type === 'footnoteDefinition')
+    .map((n: any) => n.attrs?.id);
+}
+
+function definitionText(content: any, id: string): string | undefined {
+  const list = (content.content ?? []).find(
+    (n: any) => n.type === 'footnotesList',
+  );
+  const def = (list?.content ?? []).find(
+    (n: any) => n.type === 'footnoteDefinition' && n.attrs?.id === id,
+  );
+  return def?.content?.[0]?.content?.[0]?.text;
+}
+
+describe('ImportService.importPage — footnote canonicalization (#228)', () => {
+  it('orders footnotes by first reference, dedupes reuse, and drops orphans', async () => {
+    const { service, getCaptured } = makeService();
+
+    await service.importPage(
+      Promise.resolve(makeFile('note.md', MARKDOWN)),
+      'user-id',
+      'space-id',
+      'workspace-id',
+    );
+
+    const content = getCaptured().content;
+    expect(content).toBeTruthy();
+
+    // Reference order is c, a, b (NOT the markdown definition order a, b, c).
+    expect(footnoteListIds(content)).toEqual(['c', 'a', 'b']);
+
+    // Definitions preserved and attached to the right ids.
+    expect(definitionText(content, 'c')).toBe('note C');
+    expect(definitionText(content, 'a')).toBe('note A');
+    expect(definitionText(content, 'b')).toBe('note B');
+
+    // Orphan definition [^z] is dropped.
+    expect(footnoteListIds(content)).not.toContain('z');
+
+    // Reused [^a] yields exactly ONE definition, and exactly one list.
+    const lists = (content.content ?? []).filter(
+      (n: any) => n.type === 'footnotesList',
+    );
+    expect(lists).toHaveLength(1);
+    expect(footnoteListIds(content).filter((id) => id === 'a')).toHaveLength(1);
+  });
+
+  it('is idempotent: canonicalizing the stored output again is a no-op', async () => {
+    const { service, getCaptured } = makeService();
+    await service.importPage(
+      Promise.resolve(makeFile('note.md', MARKDOWN)),
+      'user-id',
+      'space-id',
+      'workspace-id',
+    );
+    const stored = getCaptured().content;
+
+    // The stored content is already canonical; running the canonicalizer a second
+    // time must not change it (safe to wire into every write path).
+    const second = canonicalizeFootnotes(stored);
+    expect(second).toEqual(stored);
+    expect(footnoteListIds(second)).toEqual(['c', 'a', 'b']);
+  });
+});
diff --git a/apps/server/src/integrations/import/services/import.service.ts b/apps/server/src/integrations/import/services/import.service.ts
index 19bffe8d..75418e55 100644
--- a/apps/server/src/integrations/import/services/import.service.ts
+++ b/apps/server/src/integrations/import/services/import.service.ts
@@ -17,7 +17,7 @@ import {
 import { generateJitteredKeyBetween } from 'fractional-indexing-jittered';
 import { TiptapTransformer } from '@hocuspocus/transformer';
 import * as Y from 'yjs';
-import { markdownToHtml } from '@docmost/editor-ext';
+import { markdownToHtml, canonicalizeFootnotes } from '@docmost/editor-ext';
 import {
   FileTaskStatus,
   FileTaskType,
@@ -85,7 +85,17 @@ export class ImportService {
 
     const extracted = this.extractTitleAndRemoveHeading(prosemirrorState);
     const title = extracted.title;
-    const prosemirrorJson = extracted.prosemirrorJson;
+    // Imported markdown/HTML is built via markdownToHtml -> htmlToJson, which
+    // never runs the editor's footnoteSyncPlugin, so the footnote topology keeps
+    // the source's PHYSICAL definition order (out of order vs. references),
+    // retains orphan definitions, and is not deduped. Canonicalize before
+    // persisting so the stored page matches the editor's invariant (issue #228).
+    // Pure + idempotent + shape-safe: a doc with no footnotes is unchanged.
+    // (Future consolidation, architecture B: this import path persists directly
+    // via pageRepo.insertPage rather than through PageService.createPage, so the
+    // canonicalize call lives here; folding both into one "prepare JSON for
+    // persist" helper is a sensible follow-up.)
+    const prosemirrorJson = canonicalizeFootnotes(extracted.prosemirrorJson);
 
     const pageTitle = title || fileName;
 
diff --git a/packages/editor-ext/src/lib/footnote/footnote-canonicalize.test.ts b/packages/editor-ext/src/lib/footnote/footnote-canonicalize.test.ts
new file mode 100644
index 00000000..4bc17bb6
--- /dev/null
+++ b/packages/editor-ext/src/lib/footnote/footnote-canonicalize.test.ts
@@ -0,0 +1,371 @@
+import { describe, it, expect } from 'vitest';
+import { Editor, getSchema } from '@tiptap/core';
+import { Document } from '@tiptap/extension-document';
+import { Paragraph } from '@tiptap/extension-paragraph';
+import { Text } from '@tiptap/extension-text';
+import { FootnoteReference } from './footnote-reference';
+import { FootnotesList } from './footnotes-list';
+import { FootnoteDefinition } from './footnote-definition';
+import { canonicalizeFootnotes } from './footnote-canonicalize';
+import { FOOTNOTE_CORPUS } from './footnote-corpus';
+import {
+  collectReferenceIds,
+  computeFootnoteNumbers,
+  FOOTNOTE_REFERENCE_NAME,
+  FOOTNOTES_LIST_NAME,
+  FOOTNOTE_DEFINITION_NAME,
+} from './footnote-util';
+import { Node as PMNode } from '@tiptap/pm/model';
+
+const extensions = [
+  Document,
+  Paragraph,
+  Text,
+  FootnoteReference,
+  FootnotesList,
+  FootnoteDefinition,
+];
+
+const ref = (id: string) => ({ type: FOOTNOTE_REFERENCE_NAME, attrs: { id } });
+const def = (id: string, text?: string) => ({
+  type: FOOTNOTE_DEFINITION_NAME,
+  attrs: { id },
+  content: [
+    text
+      ? { type: 'paragraph', content: [{ type: 'text', text }] }
+      : { type: 'paragraph' },
+  ],
+});
+const list = (...defs: any[]) => ({ type: FOOTNOTES_LIST_NAME, content: defs });
+const para = (...inline: any[]) => ({ type: 'paragraph', content: inline });
+
+/** Find every node of `type`, document order. */
+function findAll(node: any, type: string, acc: any[] = []): any[] {
+  if (!node || typeof node !== 'object') return acc;
+  if (node.type === type) acc.push(node);
+  if (Array.isArray(node.content)) {
+    for (const c of node.content) findAll(c, type, acc);
+  }
+  return acc;
+}
+
+/** Physical id order of the definitions in the (single) footnotesList. */
+function defOrder(doc: any): string[] {
+  return findAll(doc, FOOTNOTE_DEFINITION_NAME).map((d) => d.attrs.id);
+}
+
+const schema = getSchema(extensions);
+/** Reference order (distinct, document order) computed via the shared util. */
+function refOrder(doc: any): string[] {
+  return collectReferenceIds(PMNode.fromJSON(schema, doc));
+}
+
+describe('canonicalizeFootnotes (pure JSON)', () => {
+  it('orders definitions by FIRST reference (out-of-order list -> 1..N)', () => {
+    // References appear b, a, d, c; the bottom list is in a different (import)
+    // order. The canonical list must follow reference order so reading it top to
+    // bottom yields numbers 1..N.
+    const doc = {
+      type: 'doc',
+      content: [
+        para(
+          { type: 'text', text: 'x' },
+          ref('b'),
+          ref('a'),
+          ref('d'),
+          ref('c'),
+        ),
+        list(def('a', 'A'), def('c', 'C'), def('b', 'B'), def('d', 'D')),
+      ],
+    };
+
+    const out = canonicalizeFootnotes(doc);
+    expect(defOrder(out)).toEqual(['b', 'a', 'd', 'c']);
+    // The physical definition order now matches reference order, so the derived
+    // numbers (1..N) run sequentially down the list.
+    expect(refOrder(out)).toEqual(['b', 'a', 'd', 'c']);
+    const numbers = computeFootnoteNumbers(PMNode.fromJSON(schema, out));
+    expect(numbers.get('b')).toBe(1);
+    expect(numbers.get('a')).toBe(2);
+    expect(numbers.get('d')).toBe(3);
+    expect(numbers.get('c')).toBe(4);
+  });
+
+  it('numbers run 1..N down the canonical list', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'x' }, ref('b'), ref('a'), ref('c')),
+        list(def('a', 'A'), def('c', 'C'), def('b', 'B')),
+      ],
+    };
+    const out = canonicalizeFootnotes(doc);
+    // Definition order == reference order == 1,2,3 reading down.
+    expect(defOrder(out)).toEqual(['b', 'a', 'c']);
+  });
+
+  it('drops an orphan definition (no matching reference)', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'x' }, ref('a')),
+        list(def('a', 'A'), def('orphan', 'O')),
+      ],
+    };
+    const out = canonicalizeFootnotes(doc);
+    expect(defOrder(out)).toEqual(['a']);
+    expect(findAll(out, FOOTNOTE_DEFINITION_NAME)).toHaveLength(1);
+  });
+
+  it('with NO references, removes the footnotesList entirely', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'plain' }),
+        list(def('orphan', 'O')),
+      ],
+    };
+    const out = canonicalizeFootnotes(doc);
+    expect(findAll(out, FOOTNOTES_LIST_NAME)).toHaveLength(0);
+    expect(findAll(out, FOOTNOTE_DEFINITION_NAME)).toHaveLength(0);
+  });
+
+  it('reuse: repeated references collapse to ONE definition/number', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para(ref('d'), { type: 'text', text: ' a ' }, ref('d'), ref('d')),
+        list(def('d', 'shared')),
+      ],
+    };
+    const out = canonicalizeFootnotes(doc);
+    // One definition; the three references keep id "d".
+    expect(defOrder(out)).toEqual(['d']);
+    expect(
+      findAll(out, FOOTNOTE_REFERENCE_NAME).map((r) => r.attrs.id),
+    ).toEqual(['d', 'd', 'd']);
+  });
+
+  it('duplicate definitions: first wins, the rest are dropped (never resurface as orphans)', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'x' }, ref('d')),
+        list(def('d', 'first'), def('d', 'second'), def('d', 'third')),
+      ],
+    };
+    const out = canonicalizeFootnotes(doc);
+    const defs = findAll(out, FOOTNOTE_DEFINITION_NAME);
+    expect(defs.map((d) => d.attrs.id)).toEqual(['d']);
+    expect(defs[0].content[0].content[0].text).toBe('first');
+  });
+
+  it('synthesizes an empty definition for a reference that has none', () => {
+    const doc = {
+      type: 'doc',
+      content: [para({ type: 'text', text: 'x' }, ref('missing'))],
+    };
+    const out = canonicalizeFootnotes(doc);
+    expect(defOrder(out)).toEqual(['missing']);
+    const list0 = findAll(out, FOOTNOTES_LIST_NAME);
+    expect(list0).toHaveLength(1);
+  });
+
+  it('merges multiple footnotesList nodes into one', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'a' }, ref('x'), ref('y')),
+        list(def('x', 'X')),
+        para({ type: 'text', text: 'tail' }),
+        list(def('y', 'Y')),
+      ],
+    };
+    const out = canonicalizeFootnotes(doc);
+    expect(findAll(out, FOOTNOTES_LIST_NAME)).toHaveLength(1);
+    expect(defOrder(out)).toEqual(['x', 'y']);
+  });
+
+  it('places the single list before trailing empty paragraphs', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'x' }, ref('a')),
+        list(def('a', 'A')),
+        { type: 'paragraph' },
+      ],
+    };
+    const out = canonicalizeFootnotes(doc);
+    const last = out.content[out.content.length - 1];
+    expect(last.type).toBe('paragraph');
+    expect(out.content[out.content.length - 2].type).toBe(FOOTNOTES_LIST_NAME);
+  });
+
+  it('is idempotent: canonicalize(canonicalize(x)) === canonicalize(x)', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'x' }, ref('b'), ref('a')),
+        list(def('a', 'A'), def('b', 'B'), def('orphan', 'O')),
+      ],
+    };
+    const once = canonicalizeFootnotes(doc);
+    const twice = canonicalizeFootnotes(once);
+    expect(twice).toEqual(once);
+  });
+
+  it('does not mutate its input', () => {
+    const doc = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'x' }, ref('a')),
+        list(def('orphan', 'O')),
+      ],
+    };
+    const snapshot = JSON.parse(JSON.stringify(doc));
+    canonicalizeFootnotes(doc);
+    expect(doc).toEqual(snapshot);
+  });
+});
+
+/**
+ * GOLDEN PARITY against the live `footnoteSyncPlugin`. The server canonicalizer
+ * must produce EXACTLY what the editor keeps. For every editor-reachable steady
+ * state (the list is already reference-ordered there), driving a real editor to
+ * convergence and then running `canonicalizeFootnotes` on its JSON must be a
+ * byte-for-byte no-op — proving the server output is identical to the editor's.
+ */
+describe('canonicalizeFootnotes golden parity with footnoteSyncPlugin', () => {
+  function makeEditor(content: any) {
+    return new Editor({ extensions, content });
+  }
+
+  /** Load `content`, fire one local edit so the sync plugin converges, return JSON. */
+  function pluginSteadyState(content: any): any {
+    const editor = makeEditor(content);
+    // A local doc change triggers footnoteSyncPlugin.appendTransaction.
+    editor.commands.insertContentAt(1, ' ');
+    const json = editor.state.doc.toJSON();
+    editor.destroy();
+    return json;
+  }
+
+  const corpus: Array<{ name: string; content: any }> = [
+    {
+      name: 'plain ref + def',
+      content: {
+        type: 'doc',
+        content: [para({ type: 'text', text: 'a' }, ref('x')), list(def('x', 'X'))],
+      },
+    },
+    {
+      name: 'two refs, two defs in reference order',
+      content: {
+        type: 'doc',
+        content: [
+          para({ type: 'text', text: 'a' }, ref('x'), { type: 'text', text: 'b' }, ref('y')),
+          list(def('x', 'X'), def('y', 'Y')),
+        ],
+      },
+    },
+    {
+      name: 'orphan definition gets removed',
+      content: {
+        type: 'doc',
+        content: [para({ type: 'text', text: 'a' }, ref('x')), list(def('x', 'X'), def('orphan', 'O'))],
+      },
+    },
+    {
+      name: 'reference missing its definition (synth empty)',
+      content: {
+        type: 'doc',
+        content: [para({ type: 'text', text: 'a' }, ref('x'))],
+      },
+    },
+    {
+      name: 'reuse: repeated references, one definition',
+      content: {
+        type: 'doc',
+        content: [
+          para(ref('d'), { type: 'text', text: ' a ' }, ref('d'), ref('d')),
+          list(def('d', 'shared')),
+        ],
+      },
+    },
+    {
+      name: 'no footnotes at all',
+      content: {
+        type: 'doc',
+        content: [para({ type: 'text', text: 'just text' })],
+      },
+    },
+  ];
+
+  for (const { name, content } of corpus) {
+    it(`steady state is a canonicalize no-op: ${name}`, () => {
+      const steady = pluginSteadyState(content);
+      expect(canonicalizeFootnotes(steady)).toEqual(steady);
+    });
+  }
+
+  it('placement parity: the LIVE plugin leaves a list with NON-EMPTY content after it in place, and canonicalize agrees', () => {
+    // Drives the real footnoteSyncPlugin (not a hand-authored expected): a single
+    // canonical list with body content AFTER it must NOT be repositioned by the
+    // plugin, and the server canonicalizer must agree (step-6 placement parity).
+    const content = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'a' }, ref('x')),
+        list(def('x', 'X')),
+        para({ type: 'text', text: 'epilogue' }),
+      ],
+    };
+    const steady = pluginSteadyState(content);
+    // The plugin did NOT move the list to the end: a non-empty paragraph follows it.
+    const types = steady.content.map((n: any) => n.type);
+    const listPos = types.indexOf(FOOTNOTES_LIST_NAME);
+    expect(listPos).toBeGreaterThanOrEqual(0);
+    expect(listPos).toBeLessThan(types.length - 1);
+    const after = steady.content[listPos + 1];
+    expect(after.type).toBe('paragraph');
+    expect(JSON.stringify(after)).toContain('epilogue');
+    // The canonicalizer is a byte-for-byte no-op on that steady state (parity).
+    expect(canonicalizeFootnotes(steady)).toEqual(steady);
+  });
+
+  it('the canonicalizer and the editor agree on reference order and definition set', () => {
+    const content = {
+      type: 'doc',
+      content: [
+        para({ type: 'text', text: 'a' }, ref('x'), { type: 'text', text: 'b' }, ref('y')),
+        list(def('y', 'Y'), def('x', 'X')), // physically reversed
+      ],
+    };
+    const steady = pluginSteadyState(content);
+    const canon = canonicalizeFootnotes(content);
+    // Same reference order and same DEFINITION SET (ids) in both, even though the
+    // physical list order may differ (the plugin preserves node identity, the
+    // canonicalizer reorders). Numbering — derived from reference order — matches.
+    expect(refOrder(steady)).toEqual(['x', 'y']);
+    expect(defOrder(canon)).toEqual(['x', 'y']);
+    expect(new Set(defOrder(steady))).toEqual(new Set(defOrder(canon)));
+  });
+});
+
+/**
+ * SHARED golden corpus: this editor-ext copy of `canonicalizeFootnotes` and the
+ * MCP mirror (`packages/mcp/src/lib/footnote-canonicalize.ts`) are BOTH run
+ * against the identical { input -> expected } corpus. Pinning the same expected
+ * outputs in both suites makes "the two pure copies behave identically" a
+ * checkable property without coupling the packages (architecture item A). The
+ * MCP mirror of these assertions lives in `test/unit/footnote-corpus.test.mjs`.
+ */
+describe('canonicalizeFootnotes shared golden corpus (editor-ext copy)', () => {
+  for (const { name, input, expected } of FOOTNOTE_CORPUS) {
+    it(`matches the corpus expected output: ${name}`, () => {
+      expect(canonicalizeFootnotes(input)).toEqual(expected);
+      // Idempotent on the corpus too.
+      expect(canonicalizeFootnotes(expected)).toEqual(expected);
+    });
+  }
+});
diff --git a/packages/editor-ext/src/lib/footnote/footnote-canonicalize.ts b/packages/editor-ext/src/lib/footnote/footnote-canonicalize.ts
new file mode 100644
index 00000000..f7a05f94
--- /dev/null
+++ b/packages/editor-ext/src/lib/footnote/footnote-canonicalize.ts
@@ -0,0 +1,272 @@
+import {
+  FOOTNOTE_REFERENCE_NAME,
+  FOOTNOTES_LIST_NAME,
+  FOOTNOTE_DEFINITION_NAME,
+} from './footnote-util';
+
+/**
+ * Server-side, EditorView-free port of the footnote integrity invariant that
+ * `footnoteSyncPlugin` maintains in the live editor. Where the plugin is an
+ * `appendTransaction` that only runs inside a ProseMirror `EditorView`, this is
+ * a PURE function over ProseMirror JSON: `canonicalizeFootnotes(doc) -> doc`.
+ *
+ * It exists because the NON-editor write paths served by THIS copy build
+ * ProseMirror JSON directly (never running the editor's plugins), so the
+ * canonical footnote topology was never enforced on those writes. The consumers
+ * of this editor-ext copy are: the server markdown/HTML import
+ * (`markdownToHtml -> htmlToJson` in import.service / file-import-task.service),
+ * `PageService` create/update (`parseProsemirrorContent` for the JSON/markdown/
+ * HTML REST write paths), and the client markdown PASTE path
+ * (`markdown-clipboard.ts`). (The MCP package mirrors this canonicalizer in
+ * `packages/mcp/src/lib/footnote-canonicalize.ts` for its own FULL-document write
+ * paths — `markdownToProseMirrorCanonical` (the page markdown-import path; the
+ * plain `markdownToProseMirror` primitive used for COMMENT bodies does NOT
+ * canonicalize), `update_page_json`, `docmost_transform`, `insert_footnote`,
+ * `copy_page_content` — see that file's header.) All of these are the root cause
+ * of the symptom in the issue: footnotes rendered out of order (`1, 4, 2, 3, …`),
+ * a raw trailing `[^id]: …` block, and orphan definitions, all of which are
+ * simply the result of content written PAST the canonicalizer.
+ *
+ * The desired end-state (identical to the plugin's) is:
+ *
+ *   1. Reference ids in DOCUMENT ORDER are the single source of truth for which
+ *      definitions exist and in what order (numbering is derived from this, see
+ *      `computeFootnoteNumbers`). Repeated references that share an id are REUSE
+ *      (one footnote, one number, one definition) — never re-id'd.
+ *   2. Exactly ONE `footnotesList`, holding one definition per referenced id in
+ *      REFERENCE order, reusing the existing definition node (content preserved)
+ *      or synthesizing an empty one when missing. The list sits after the last
+ *      meaningful block (only trailing empty paragraphs may follow it).
+ *   3. Orphan definitions (no matching reference) are dropped.
+ *   4. Duplicate DEFINITIONS (two nodes sharing an id) are resolved first-wins:
+ *      the first definition for an id is kept; later duplicates carry the SAME
+ *      id, so they can never be referenced separately and are simply dropped.
+ *      This matches the importer's first-wins rule ("one definition per id").
+ *      (The LIVE editor instead re-id's a duplicate definition so a paste/collab
+ *      merge cannot silently lose live user data; the artifacts this copy
+ *      sanitizes are agent/import-authored, so first-wins is the right policy —
+ *      see footnote-sync.ts `resolveCollisions`.)
+ *   5. Idempotent: a document that already satisfies the invariant is returned
+ *      structurally unchanged (the existing definition/list nodes are reused
+ *      verbatim), so re-running the canonicalizer — or running it on a write that
+ *      the editor already canonicalized — is a no-op. This is what makes it safe
+ *      to wire into EVERY write path without spurious mutations / git-sync churn.
+ *
+ * Divergence from the live plugin (intentional): the plugin preserves the
+ * PHYSICAL order of existing definition nodes to keep their Yjs/CRDT subtree
+ * identity stable across collaborators (numbering is decoration-derived, so the
+ * displayed numbers are correct regardless of physical order). This function has
+ * no live CRDT to protect, so when a REPAIR is needed it physically REORDERS the
+ * list into reference order — which is exactly the fix the out-of-order import
+ * needs.
+ *
+ * Placement PARITY with the plugin: when the document is already in the canonical
+ * single-list state, this function leaves that list EXACTLY where it sits (it
+ * does not move it to the end). The plugin behaves the same — it treats one
+ * footnotesList holding the canonical definition set as canonical regardless of
+ * whether content follows it (footnote-sync.ts: `primaryList` falls back to the
+ * last list and `noChangeNeeded` stays true). So on every editor-reachable steady
+ * state the two agree byte-for-byte, including when non-empty content follows the
+ * list; see the golden parity test and the shared corpus.
+ *
+ * Pure: deep-clones its input, never mutates the caller's object, and is
+ * deterministic (no `Math.random`/`Date.now`).
+ */
+export function canonicalizeFootnotes<T = any>(doc: T): T {
+  if (
+    doc == null ||
+    typeof doc !== 'object' ||
+    !Array.isArray((doc as any).content)
+  ) {
+    return doc;
+  }
+  const out = cloneJson(doc) as any;
+
+  // 1) Distinct reference ids in document order (deep — references can live in
+  //    callouts, tables, list items, ...). This is the ordering/numbering truth.
+  const referenceIds: string[] = [];
+  const seenRefIds = new Set<string>();
+  collectReferenceIds(out, referenceIds, seenRefIds);
+
+  // 2) Every definition node in document order (deep — defs normally live inside
+  //    one or more `footnotesList` blocks, but we tolerate stray placements).
+  const defNodes: any[] = [];
+  collectDefinitions(out, defNodes);
+
+  // 3) First definition per id wins. Later duplicates carry the SAME id, so they
+  //    can never be referenced separately and would be orphans — they are simply
+  //    dropped (first-wins; see the file header, item 4).
+  const defById = new Map<string, any>();
+  for (const d of defNodes) {
+    const id = d?.attrs?.id;
+    if (id && !defById.has(id)) defById.set(id, d);
+  }
+
+  // 4) Build the ordered definition list: one per referenced id, in REFERENCE
+  //    order, reusing the existing node (content preserved, id normalized) or
+  //    synthesizing an empty definition. Definitions whose id is NOT referenced
+  //    are orphans and are simply never added. The reused node is SHALLOW-copied
+  //    (id normalized): `out` is already a deep clone and the old lists are cut,
+  //    so a second per-definition deep clone is needless.
+  const orderedDefs: any[] = [];
+  for (const id of referenceIds) {
+    const existing = defById.get(id);
+    if (existing) {
+      orderedDefs.push({
+        ...existing,
+        attrs: { ...(existing.attrs ?? {}), id },
+      });
+    } else {
+      orderedDefs.push(emptyDefinition(id));
+    }
+  }
+
+  // 5) No references -> there must be NO list at all (at any depth).
+  if (referenceIds.length === 0) {
+    stripFootnotesListsDeep(out);
+    return out;
+  }
+
+  // 6) Placement parity with the live plugin: when the document is ALREADY in the
+  //    canonical single-list state, leave that list exactly where it sits instead
+  //    of cutting and re-inserting it at the end. The plugin never repositions a
+  //    sole correct list (footnote-sync.ts), so moving it here would silently
+  //    reorder any user content that follows the list on the first write. The doc
+  //    is in that state when there is exactly one top-level footnotesList, every
+  //    definition in the doc is referenced (no orphans / duplicates: the def count
+  //    equals the canonical count), and the list already holds exactly the
+  //    canonical definitions in reference order.
+  const topLevelLists = out.content.filter(
+    (n: any) => n && n.type === FOOTNOTES_LIST_NAME,
+  );
+  if (
+    topLevelLists.length === 1 &&
+    defNodes.length === orderedDefs.length &&
+    deepEqualJson(topLevelLists[0].content, orderedDefs)
+  ) {
+    return out;
+  }
+
+  // 7) Otherwise rebuild: strip every footnotesList AND every bare
+  //    footnoteDefinition at ANY depth (collectDefinitions gathers defs
+  //    recursively, so a list nested in a callout/blockquote — or a bare
+  //    definition outside any list — would otherwise have its defs copied into the
+  //    rebuilt list while the original survives in place → duplicates) and
+  //    re-insert exactly one list after the last meaningful (non-empty paragraph)
+  //    top-level block, so it coexists with a trailing-node empty paragraph. This
+  //    both repairs a non-canonical doc and (in the import case) physically
+  //    reorders the list into reference order.
+  stripFootnotesListsDeep(out);
+  stripFootnoteDefinitionsDeep(out);
+  const top: any[] = out.content;
+  let insertAt = top.length;
+  while (insertAt > 0 && isEmptyParagraph(top[insertAt - 1])) insertAt--;
+  top.splice(insertAt, 0, { type: FOOTNOTES_LIST_NAME, content: orderedDefs });
+  out.content = top;
+  return out;
+}
+
+/** Remove every `footnotesList` node at ANY depth (mutates the given clone). */
+function stripFootnotesListsDeep(node: any): void {
+  if (!node || typeof node !== 'object' || !Array.isArray(node.content)) return;
+  node.content = node.content.filter(
+    (c: any) => !(c && c.type === FOOTNOTES_LIST_NAME),
+  );
+  for (const child of node.content) stripFootnotesListsDeep(child);
+}
+
+/**
+ * Remove every BARE `footnoteDefinition` node at ANY depth (mutates the given
+ * clone). Runs only in the rebuild path AFTER the lists are stripped, so it
+ * targets definitions that were sitting outside a list (e.g. hand-authored via a
+ * raw-JSON write path and nested in a callout); their content was already copied
+ * into the rebuilt list, so leaving the originals would duplicate them.
+ */
+function stripFootnoteDefinitionsDeep(node: any): void {
+  if (!node || typeof node !== 'object' || !Array.isArray(node.content)) return;
+  node.content = node.content.filter(
+    (c: any) => !(c && c.type === FOOTNOTE_DEFINITION_NAME),
+  );
+  for (const child of node.content) stripFootnoteDefinitionsDeep(child);
+}
+
+/**
+ * Deep equality over plain JSON: arrays are compared POSITIONALLY
+ * (order-SENSITIVE), object keys order-insensitively. The array order-sensitivity
+ * is required for correctness here — a reordered `footnotesList.content` must
+ * compare UNEQUAL so the canonical rebuild fires instead of leaving it in place.
+ */
+function deepEqualJson(a: any, b: any): boolean {
+  if (a === b) return true;
+  if (a == null || b == null || typeof a !== typeof b) return false;
+  if (Array.isArray(a) || Array.isArray(b)) {
+    if (!Array.isArray(a) || !Array.isArray(b) || a.length !== b.length) {
+      return false;
+    }
+    for (let i = 0; i < a.length; i++) {
+      if (!deepEqualJson(a[i], b[i])) return false;
+    }
+    return true;
+  }
+  if (typeof a === 'object') {
+    const ka = Object.keys(a);
+    const kb = Object.keys(b);
+    if (ka.length !== kb.length) return false;
+    for (const k of ka) {
+      if (!Object.prototype.hasOwnProperty.call(b, k)) return false;
+      if (!deepEqualJson(a[k], b[k])) return false;
+    }
+    return true;
+  }
+  return false;
+}
+
+/** A fresh empty definition node for a referenced id with no definition. */
+function emptyDefinition(id: string): any {
+  return {
+    type: FOOTNOTE_DEFINITION_NAME,
+    attrs: { id },
+    content: [{ type: 'paragraph' }],
+  };
+}
+
+function isEmptyParagraph(node: any): boolean {
+  return (
+    !!node &&
+    node.type === 'paragraph' &&
+    (!Array.isArray(node.content) || node.content.length === 0)
+  );
+}
+
+/** Collect DISTINCT footnoteReference ids in document order (first appearance). */
+function collectReferenceIds(
+  node: any,
+  out: string[],
+  seen: Set<string>,
+): void {
+  if (!node || typeof node !== 'object') return;
+  if (node.type === FOOTNOTE_REFERENCE_NAME) {
+    const id = node?.attrs?.id;
+    if (id && !seen.has(id)) {
+      seen.add(id);
+      out.push(id);
+    }
+  }
+  if (Array.isArray(node.content)) {
+    for (const child of node.content) collectReferenceIds(child, out, seen);
+  }
+}
+
+/** Collect every footnoteDefinition node in document order. */
+function collectDefinitions(node: any, out: any[]): void {
+  if (!node || typeof node !== 'object') return;
+  if (node.type === FOOTNOTE_DEFINITION_NAME) out.push(node);
+  if (Array.isArray(node.content)) {
+    for (const child of node.content) collectDefinitions(child, out);
+  }
+}
+
+function cloneJson<T>(v: T): T {
+  if (typeof structuredClone === 'function') return structuredClone(v);
+  return JSON.parse(JSON.stringify(v)) as T;
+}
diff --git a/packages/editor-ext/src/lib/footnote/footnote-corpus.ts b/packages/editor-ext/src/lib/footnote/footnote-corpus.ts
new file mode 100644
index 00000000..dd5f41d0
--- /dev/null
+++ b/packages/editor-ext/src/lib/footnote/footnote-corpus.ts
@@ -0,0 +1,1271 @@
+/**
+ * SHARED golden corpus for the footnote canonicalizer (issue #228).
+ *
+ * Each case is { name, input, expected } where `expected` is exactly what
+ * `canonicalizeFootnotes(input)` must return. This is the CANONICAL copy; it is
+ * mirrored verbatim (data only) in `packages/mcp/test/unit/footnote-corpus.mjs`.
+ * Both the editor-ext copy and the MCP mirror of `canonicalizeFootnotes` are run
+ * against this corpus by their respective test suites, which turns "the two
+ * pure copies behave identically" into a checkable property without coupling the
+ * packages. When you change one corpus, change the other.
+ *
+ * Coverage includes (besides ordering/orphan/reuse/dedup/synth/merge): a single
+ * canonical list with NON-EMPTY content after it (must NOT be repositioned —
+ * plugin placement parity, must-fix #2), a reference nested inside a callout
+ * (the recursive collection, test-coverage #14), and a BARE footnoteDefinition
+ * nested in a callout (rebuild must strip the original so it is not duplicated).
+ */
+export interface FootnoteCorpusCase {
+  name: string;
+  input: any;
+  expected: any;
+}
+
+export const FOOTNOTE_CORPUS: FootnoteCorpusCase[] = [
+  {
+    "name": "out-of-order defs ordered by first reference",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "b"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "c"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "c"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "C"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "b"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "B"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "D"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "b"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "c"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "b"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "B"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "D"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "c"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "C"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "orphan definition dropped",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "orphan"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "O"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "no references removes the list",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "plain"
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "orphan"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "O"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "plain"
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "reuse: repeated references collapse to one definition",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "text",
+              "text": " a "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "shared"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "text",
+              "text": " a "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "shared"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "duplicate definitions: first wins",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "first"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "second"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "third"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "first"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "synthesizes an empty definition for a reference with none",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "missing"
+              }
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "missing"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "missing"
+              },
+              "content": [
+                {
+                  "type": "paragraph"
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "merges multiple footnotesList nodes into one",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "a"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "x"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "y"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "x"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "X"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "tail"
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "y"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "Y"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "a"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "x"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "y"
+              }
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "tail"
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "x"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "X"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "y"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "Y"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "single canonical list before a trailing empty paragraph stays put",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph"
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph"
+        }
+      ]
+    }
+  },
+  {
+    "name": "single canonical list with NON-EMPTY content after it is NOT moved (plugin parity)",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "epilogue text"
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "epilogue text"
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "reference inside a nested container (callout) is collected",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "callout",
+          "content": [
+            {
+              "type": "paragraph",
+              "content": [
+                {
+                  "type": "text",
+                  "text": "see "
+                },
+                {
+                  "type": "footnoteReference",
+                  "attrs": {
+                    "id": "n"
+                  }
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "n"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "callout",
+          "content": [
+            {
+              "type": "paragraph",
+              "content": [
+                {
+                  "type": "text",
+                  "text": "see "
+                },
+                {
+                  "type": "footnoteReference",
+                  "attrs": {
+                    "id": "n"
+                  }
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "n"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "bare footnoteDefinition nested in a callout is collected, NOT duplicated",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "see "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "callout",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "see "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "callout",
+          "content": []
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "no footnotes at all is unchanged",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "just text"
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "just text"
+            }
+          ]
+        }
+      ]
+    }
+  }
+];
diff --git a/packages/editor-ext/src/lib/footnote/index.ts b/packages/editor-ext/src/lib/footnote/index.ts
index 02defff1..f3cafac3 100644
--- a/packages/editor-ext/src/lib/footnote/index.ts
+++ b/packages/editor-ext/src/lib/footnote/index.ts
@@ -4,3 +4,4 @@ export * from "./footnotes-list";
 export * from "./footnote-definition";
 export * from "./footnote-numbering";
 export * from "./footnote-sync";
+export * from "./footnote-canonicalize";
diff --git a/packages/editor-ext/tsconfig.json b/packages/editor-ext/tsconfig.json
index a4ad0d72..5fcc2435 100644
--- a/packages/editor-ext/tsconfig.json
+++ b/packages/editor-ext/tsconfig.json
@@ -22,5 +22,11 @@
     "noFallthroughCasesInSwitch": false
   },
   "include": ["src/**/*"],
-  "exclude": ["node_modules", "dist", "src/**/*.spec.ts", "src/**/*.test.ts"]
+  "exclude": [
+    "node_modules",
+    "dist",
+    "src/**/*.spec.ts",
+    "src/**/*.test.ts",
+    "src/lib/footnote/footnote-corpus.ts"
+  ]
 }
diff --git a/packages/mcp/build/client.js b/packages/mcp/build/client.js
index a5219c5c..082f8e68 100644
--- a/packages/mcp/build/client.js
+++ b/packages/mcp/build/client.js
@@ -7,7 +7,7 @@ import { TiptapTransformer } from "@hocuspocus/transformer";
 import * as Y from "yjs";
 import WebSocket from "ws";
 import { convertProseMirrorToMarkdown } from "./lib/markdown-converter.js";
-import { updatePageContentRealtime, replacePageContent, markdownToProseMirror, mutatePageContent, buildCollabWsUrl, assertYjsEncodable, applyDocToFragment, } from "./lib/collaboration.js";
+import { updatePageContentRealtime, replacePageContent, markdownToProseMirror, markdownToProseMirrorCanonical, mutatePageContent, buildCollabWsUrl, assertYjsEncodable, applyDocToFragment, } from "./lib/collaboration.js";
 import { footnoteWarningsField } from "./lib/footnote-analyze.js";
 import { buildPageTree } from "./lib/tree.js";
 import { serializeDocmostMarkdown, parseDocmostMarkdown, } from "./lib/markdown-document.js";
@@ -17,7 +17,7 @@ import { applyTextEdits, } from "./lib/json-edit.js";
 import { getCollabToken, performLogin } from "./lib/auth-utils.js";
 import { diffDocs, summarizeChange } from "./lib/diff.js";
 import { applyAnchorInDoc, canAnchorInDoc } from "./lib/comment-anchor.js";
-import { blockText, walk, getList, insertMarkerAfter, setCalloutRange, noteItem, mdToInlineNodes, commentsToFootnotes, } from "./lib/transforms.js";
+import { blockText, walk, getList, insertMarkerAfter, setCalloutRange, noteItem, mdToInlineNodes, commentsToFootnotes, canonicalizeFootnotes, insertInlineFootnote, } from "./lib/transforms.js";
 import vm from "node:vm";
 // Supported image types, kept as two lookup tables so both a local file
 // extension and a remote Content-Type can be mapped to the same canonical set.
@@ -1063,10 +1063,15 @@ export class DocmostClient {
         // the markdown link path (which TipTap sanitizes), raw JSON could otherwise
         // inject javascript:/data: link hrefs or media srcs straight into the doc.
         this.validateDocUrls(doc);
+        // Canonicalize footnotes (idempotent): an agent-authored JSON doc cannot
+        // leave footnotes out of order, orphaned, or in multiple lists — the bottom
+        // list + numbering are always derived from reference order. No-op when the
+        // footnotes are already canonical.
+        doc = canonicalizeFootnotes(doc);
         // Write the BODY first, then the title (#159 split-brain): a failed body
         // write (e.g. persist timeout) must not leave a new title over the old body.
         const collabToken = await this.getCollabTokenWithReauth();
-        const mutation = await replacePageContent(pageId, doc, collabToken, this.apiUrl);
+        const mutation = await this.replacePage(pageId, doc, collabToken, this.apiUrl);
         // Body persisted successfully — now it is safe to set the title.
         if (title) {
             await this.client.post("/pages/update", { pageId, title });
@@ -1079,6 +1084,73 @@ export class DocmostClient {
             verify: mutation.verify,
         };
     }
+    /**
+     * AUTHOR-INLINE footnote insertion. The agent supplies only WHERE
+     * (`anchorText`, a snippet of body text to attach the marker after) and WHAT
+     * (`text`, the footnote content as markdown). Numbering and the bottom
+     * `footnotesList` are derived deterministically server-side
+     * (`insertInlineFootnote` -> `canonicalizeFootnotes`): the agent never sees,
+     * assigns, or edits a footnote number or the list, so it CANNOT desync.
+     *
+     * Content DEDUP: when an existing definition has the same content, its id is
+     * reused (one number, one definition, several references). The write is atomic
+     * via `mutatePageContent` (single-writer, page-locked); if the anchor text is
+     * not found the transform aborts with a clear error and no write happens.
+     */
+    async insertFootnote(pageId, anchorText, text) {
+        await this.ensureAuthenticated();
+        if (!anchorText || !anchorText.trim()) {
+            throw new Error("insert_footnote: anchorText is required");
+        }
+        if (text == null || `${text}`.trim() === "") {
+            throw new Error("insert_footnote: text is required");
+        }
+        const collabToken = await this.getCollabTokenWithReauth();
+        let result = null;
+        const mutation = await this.mutatePage(pageId, collabToken, this.apiUrl, (liveDoc) => {
+            const r = insertInlineFootnote(liveDoc, { anchorText, text });
+            if (!r.inserted) {
+                // Abort the page-locked write by throwing: mutatePageContent does not
+                // persist when the transform throws, so a missing anchor leaves the
+                // page untouched (no partial write).
+                throw new Error(`insert_footnote: anchor text not found: ${JSON.stringify(anchorText.slice(0, 80))}`);
+            }
+            result = { footnoteId: r.footnoteId, reused: r.reused };
+            return r.doc;
+        });
+        // The not-found path throws inside the transform (aborting mutatePage), so by
+        // here `result` is always set.
+        const r = result;
+        return {
+            success: true,
+            modified: true,
+            pageId,
+            footnoteId: r.footnoteId,
+            reused: r.reused,
+            message: r.reused
+                ? "Footnote inserted (reused an existing same-content definition)."
+                : "Footnote inserted.",
+            verify: mutation.verify,
+        };
+    }
+    /**
+     * Page-locked write seam over collaboration.mutatePageContent. Production just
+     * delegates; it exists as an overridable method so the insert_footnote wrapper
+     * (transform abort-on-not-found + response shaping) can be unit-tested without
+     * standing up a live Hocuspocus collab socket.
+     */
+    mutatePage(pageId, collabToken, apiUrl, transform) {
+        return mutatePageContent(pageId, collabToken, apiUrl, transform);
+    }
+    /**
+     * Full-document write seam over collaboration.replacePageContent. Production
+     * just delegates; it exists as an overridable method so the full-doc write
+     * tools (update_page_json, copy_page_content) can have their footnote-
+     * canonicalization binding unit-tested without a live Hocuspocus collab socket.
+     */
+    replacePage(pageId, doc, collabToken, apiUrl) {
+        return replacePageContent(pageId, doc, collabToken, apiUrl);
+    }
     /**
      * Export a page to a single self-contained Docmost-flavoured markdown file:
      * meta block + body (with inline comment anchors + diagrams) + comment
@@ -1120,7 +1192,8 @@ export class DocmostClient {
     async importPageMarkdown(pageId, fullMarkdown) {
         await this.ensureAuthenticated();
         const { meta, body, comments } = parseDocmostMarkdown(fullMarkdown);
-        const doc = await markdownToProseMirror(body);
+        // PAGE import: canonicalize footnotes (see markdownToProseMirrorCanonical).
+        const doc = await markdownToProseMirrorCanonical(body);
         const collabToken = await this.getCollabTokenWithReauth();
         const mutation = await replacePageContent(pageId, doc, collabToken, this.apiUrl);
         // Collect distinct comment ids that actually became comment marks in the doc.
@@ -1200,13 +1273,18 @@ export class DocmostClient {
         // uses, so copying never lands a javascript:/data: href/src on the target
         // (parity with updatePageJson; harmless for already-stored source content).
         this.validateDocUrls(content);
+        // Defense-in-depth (#228): this is a FULL-document write, so canonicalize
+        // footnotes before copying — a no-op on already-canonical source content, but
+        // it guarantees a copy can never propagate a non-canonical footnote topology
+        // to the target (parity with the other full-doc write paths).
+        const canonical = canonicalizeFootnotes(content);
         const collabToken = await this.getCollabTokenWithReauth();
-        const mutation = await replacePageContent(targetPageId, content, collabToken, this.apiUrl);
+        const mutation = await this.replacePage(targetPageId, canonical, collabToken, this.apiUrl);
         return {
             success: true,
             sourcePageId,
             targetPageId,
-            copiedNodes: content.content.length,
+            copiedNodes: canonical.content.length,
             verify: mutation.verify,
         };
     }
@@ -1613,7 +1691,10 @@ export class DocmostClient {
                 }
             }
         }
-        // Convert through the full Docmost schema (consistent with page paths)
+        // Convert through the full Docmost schema. Deliberately the NON-canonicalizing
+        // variant: a comment body may carry a footnote definition with no matching
+        // reference, and canonicalization would drop it (data loss). See
+        // markdownToProseMirror vs markdownToProseMirrorCanonical.
         const jsonContent = await markdownToProseMirror(content);
         const payload = {
             pageId,
@@ -1701,6 +1782,7 @@ export class DocmostClient {
     }
     async updateComment(commentId, content) {
         await this.ensureAuthenticated();
+        // NON-canonicalizing on purpose (comment body — see createComment).
         const jsonContent = await markdownToProseMirror(content);
         await this.client.post("/comments/update", {
             commentId,
@@ -2422,6 +2504,8 @@ export class DocmostClient {
                 noteItem,
                 mdToInlineNodes,
                 commentsToFootnotes,
+                canonicalizeFootnotes,
+                insertInlineFootnote,
             },
         };
         // Captured oldDoc / newDoc for the diff (set inside runTransform).
@@ -2455,16 +2539,25 @@ export class DocmostClient {
             if (typeof fn !== "function") {
                 throw new Error("transform must evaluate to a function (doc, ctx) => doc");
             }
-            const result = vm.runInNewContext("f(d, c)", { f: fn, d: sandbox.doc, c: ctx }, { timeout: 5000 });
-            if (!result ||
-                typeof result !== "object" ||
-                result.type !== "doc" ||
-                !Array.isArray(result.content)) {
+            const raw = vm.runInNewContext("f(d, c)", { f: fn, d: sandbox.doc, c: ctx }, { timeout: 5000 });
+            if (!raw ||
+                typeof raw !== "object" ||
+                raw.type !== "doc" ||
+                !Array.isArray(raw.content)) {
                 throw new Error('transform must return a ProseMirror doc node ({ type:"doc", content:[...] })');
             }
-            // Validate the returned doc before it can be written.
-            this.validateDocStructure(result);
-            this.validateDocUrls(result);
+            // Validate the RAW transform output FIRST (structure — including the
+            // MAX_DEPTH guard — and URLs), mirroring updatePageJson. The canonicalizer
+            // recurses without a depth limiter, so validating after it would turn a
+            // too-deep doc into an opaque "Maximum call stack size exceeded" instead of
+            // the intended "nesting exceeds the maximum depth" error.
+            this.validateDocStructure(raw);
+            this.validateDocUrls(raw);
+            // Auto-canonicalize footnotes after the transform (idempotent): no write
+            // path can leave footnotes out of order / orphaned / in a raw `[^id]`
+            // block. In a dryRun preview this may surface footnote edits the script
+            // author did not write (the canonicalizer tidied them) — that is expected.
+            const result = canonicalizeFootnotes(raw);
             newDoc = result;
             return result;
         };
diff --git a/packages/mcp/build/index.js b/packages/mcp/build/index.js
index 7f258a19..edcad9e6 100644
--- a/packages/mcp/build/index.js
+++ b/packages/mcp/build/index.js
@@ -637,8 +637,15 @@ export function createDocmostMcpServer(config) {
             "mark-safe), setCalloutRange(doc, n) (sync a [1]…[K] callout range to " +
             "[1]…[n]), noteItem(inlineNodes) (wrap inline nodes in a listItem with a " +
             "fresh id), mdToInlineNodes(markdown) (comment markdown -> inline nodes), " +
-            "and commentsToFootnotes(doc, comments, {notesHeading}) (turn inline " +
-            "comments into numbered footnotes). Footnote convention: markers are " +
+            "commentsToFootnotes(doc, comments, {notesHeading}) (turn inline " +
+            "comments into numbered footnotes), canonicalizeFootnotes(doc) (derive " +
+            "footnote numbering + the single bottom list from reference order, drop " +
+            "orphans/duplicates — runs AUTOMATICALLY on the transform RESULT, so the " +
+            "applied (and dryRun-previewed) doc is always footnote-canonical; a dryRun " +
+            "diff may therefore show footnote tidy-ups your script did not make, and " +
+            "it is idempotent after the first run), and " +
+            "insertInlineFootnote(doc, {anchorText, text}) (author-inline footnote: " +
+            "marker + dedup'd definition, list derived). Footnote convention: markers are " +
             "plain '[N]' text in the body; the notes are an orderedList under a " +
             "heading whose text is 'Примечания переводчика'. The transform runs " +
             "sandboxed (no require/process/fs/network, 5s timeout) and must return a " +
@@ -652,7 +659,8 @@ export function createDocmostMcpServer(config) {
                 "parenthesized function). It receives a clone of the live doc and " +
                 "ctx (comments, log, consume(id), helpers: blockText/walk/getList/" +
                 "insertMarkerAfter/setCalloutRange/noteItem/mdToInlineNodes/" +
-                "commentsToFootnotes) and must return a {type:'doc'} node."),
+                "commentsToFootnotes/canonicalizeFootnotes/insertInlineFootnote) " +
+                "and must return a {type:'doc'} node."),
             dryRun: z
                 .boolean()
                 .optional()
@@ -672,6 +680,33 @@ export function createDocmostMcpServer(config) {
         });
         return jsonContent(result);
     });
+    // Tool: insert_footnote
+    server.registerTool("insert_footnote", {
+        description: "Insert an AUTHOR-INLINE footnote: you specify only WHERE (anchorText) " +
+            "and WHAT (text). The footnote marker is placed right after anchorText in " +
+            "the body, and the bottom footnotes list + the numbering are derived " +
+            "deterministically server-side. You do NOT assign a number, and you " +
+            "never see or edit the footnotes list — so footnotes cannot end up out " +
+            "of order, orphaned, or as a raw '[^id]' block. If a footnote with the " +
+            "SAME text already exists, its number is REUSED (one definition, several " +
+            "references). The write is atomic and won't clobber concurrent edits; if " +
+            "anchorText is not found, nothing is written and an error is returned.",
+        inputSchema: {
+            pageId: z.string().min(1),
+            anchorText: z
+                .string()
+                .min(1)
+                .describe("A snippet of existing body text; the footnote marker is inserted " +
+                "immediately after its first occurrence (mark-safe)."),
+            text: z
+                .string()
+                .min(1)
+                .describe("The footnote content as markdown (becomes the definition)."),
+        },
+    }, async ({ pageId, anchorText, text }) => {
+        const result = await docmostClient.insertFootnote(pageId, anchorText, text);
+        return jsonContent(result);
+    });
     // Tool: diff_page_versions
     registerShared(SHARED_TOOL_SPECS.diffPageVersions, async ({ pageId, from, to }) => {
         const result = await docmostClient.diffPageVersions(pageId, from, to);
diff --git a/packages/mcp/build/lib/collaboration.js b/packages/mcp/build/lib/collaboration.js
index 87f0ef8a..4504b8d0 100644
--- a/packages/mcp/build/lib/collaboration.js
+++ b/packages/mcp/build/lib/collaboration.js
@@ -11,6 +11,7 @@ import { docmostExtensions, docmostSchema } from "./docmost-schema.js";
 import { withPageLock } from "./page-lock.js";
 import { sanitizeForYjs, findUnstorableAttr } from "./node-ops.js";
 import { lexFootnoteLines } from "./footnote-lex.js";
+import { canonicalizeFootnotes } from "./footnote-canonicalize.js";
 import { summarizeChange } from "./diff.js";
 /**
  * Build the descriptive error for an opaque Yjs encode failure ("Unexpected
@@ -343,7 +344,20 @@ function extractFootnotes(markdown) {
         section: `<section data-footnotes>${inner}</section>`,
     };
 }
-/** Convert markdown to a ProseMirror doc using the full Docmost schema. */
+/**
+ * Convert markdown to a ProseMirror doc using the full Docmost schema.
+ *
+ * This conversion does NOT canonicalize footnotes — it is the shared, content-
+ * preserving primitive used by BOTH page write paths and COMMENT bodies
+ * (createComment / updateComment). Canonicalization MUST NOT run on a comment
+ * body: a comment may legitimately contain a footnote-definition line
+ * (`[^1]: text`) with no matching reference, and the canonicalizer drops a
+ * reference-less footnotesList — which would silently delete the comment's text.
+ *
+ * Page write paths that DO need the canonical footnote topology call
+ * `markdownToProseMirrorCanonical` instead (markdown import, update_page markdown
+ * path). Keep this function reference-loss-free.
+ */
 export async function markdownToProseMirror(markdownContent) {
     const withCallouts = await preprocessCallouts(markdownContent);
     const { body, section } = extractFootnotes(withCallouts);
@@ -351,6 +365,20 @@ export async function markdownToProseMirror(markdownContent) {
     const bridged = bridgeTaskLists(html);
     return generateJSON(bridged, docmostExtensions);
 }
+/**
+ * Page-write variant of `markdownToProseMirror`: converts markdown then enforces
+ * the canonical footnote topology. The footnote `section` markdown is emitted in
+ * DEFINITION order, but numbering derives from REFERENCE order, so without this
+ * the bottom list renders out of order (`1, 4, 2, 3, …`); orphan definitions and
+ * duplicate lists are also normalized. Idempotent — a no-op once canonical, and a
+ * no-op for footnote-free content.
+ *
+ * Use this ONLY for full-document PAGE writes (never for comment bodies, where it
+ * would drop a reference-less footnote definition — see `markdownToProseMirror`).
+ */
+export async function markdownToProseMirrorCanonical(markdownContent) {
+    return canonicalizeFootnotes(await markdownToProseMirror(markdownContent));
+}
 /**
  * Build the collaboration WebSocket URL from an API base URL:
  * switch http(s)->ws(s), strip a trailing /api, mount on /collab.
@@ -708,6 +736,8 @@ export async function replacePageContent(pageId, prosemirrorDoc, collabToken, ba
  * Tables and :::callout::: blocks survive thanks to the full schema.
  */
 export async function updatePageContentRealtime(pageId, markdownContent, collabToken, baseUrl) {
-    const tiptapJson = await markdownToProseMirror(markdownContent);
+    // PAGE write: canonicalize footnotes (markdown import builds the bottom list in
+    // definition order; numbering is reference-ordered).
+    const tiptapJson = await markdownToProseMirrorCanonical(markdownContent);
     return await mutatePageContent(pageId, collabToken, baseUrl, () => tiptapJson);
 }
diff --git a/packages/mcp/build/lib/footnote-authoring.js b/packages/mcp/build/lib/footnote-authoring.js
new file mode 100644
index 00000000..ab8d7eb2
--- /dev/null
+++ b/packages/mcp/build/lib/footnote-authoring.js
@@ -0,0 +1,88 @@
+/**
+ * Inline-authoring helpers for footnotes (MCP).
+ *
+ * These build/identify footnote DEFINITION nodes for the author-inline tool
+ * (`insertInlineFootnote` in transforms.ts): a content key to de-duplicate notes
+ * by text, a definition-node factory, and a fresh uuidv7-style id generator.
+ *
+ * Split out of `footnote-canonicalize.ts` so that module stays a pure MIRROR of
+ * the editor-ext canonicalizer (compositionally symmetric to the editor-ext
+ * copy, which keeps its authoring helpers in `footnote-util.ts`). The pure
+ * canonicalizer has no dependency on these.
+ */
+const FOOTNOTE_DEFINITION_NAME = "footnoteDefinition";
+function cloneJson(v) {
+    if (typeof structuredClone === "function")
+        return structuredClone(v);
+    return JSON.parse(JSON.stringify(v));
+}
+/**
+ * Normalized content key for de-duplicating footnote DEFINITIONS by their text.
+ *
+ * Two definitions with the same key are the SAME footnote — so the inline
+ * authoring tool reuses one id (one number, one definition, several references)
+ * instead of minting a second definition. Key = plaintext (whitespace-collapsed,
+ * trimmed) PLUS a signature of the inline mark types in order, so two notes that
+ * read the same but differ in formatting (one bold, one plain) are NOT merged.
+ * Conservative: only an exact match merges.
+ */
+export function footnoteContentKey(defNode) {
+    const parts = [];
+    const visit = (n) => {
+        if (!n || typeof n !== "object")
+            return;
+        if (n.type === "text" && typeof n.text === "string") {
+            const marks = Array.isArray(n.marks)
+                ? n.marks.map((m) => m?.type).filter(Boolean).sort().join(",")
+                : "";
+            parts.push(`${n.text}${marks}`);
+        }
+        if (Array.isArray(n.content))
+            for (const c of n.content)
+                visit(c);
+    };
+    visit(defNode);
+    // Collapse the assembled text's whitespace and trim, keeping the mark
+    // signature attached so formatting differences still distinguish notes.
+    return parts
+        .join("")
+        .replace(/[ \t\r\n]+/g, " ")
+        .trim();
+}
+/**
+ * Build a footnoteDefinition node from inline ProseMirror nodes, keyed by id.
+ */
+export function makeFootnoteDefinition(id, inlineNodes) {
+    const content = Array.isArray(inlineNodes) ? cloneJson(inlineNodes) : [];
+    return {
+        type: FOOTNOTE_DEFINITION_NAME,
+        attrs: { id },
+        content: [{ type: "paragraph", content }],
+    };
+}
+/**
+ * Generate a uuidv7-style id (time-ordered), matching editor-ext's
+ * `generateFootnoteId`. Used for a genuinely-new inline footnote id.
+ */
+export function generateFootnoteId() {
+    const now = Date.now();
+    const timeHex = now.toString(16).padStart(12, "0");
+    const rand = (length) => {
+        let s = "";
+        for (let i = 0; i < length; i++)
+            s += Math.floor(Math.random() * 16).toString(16);
+        return s;
+    };
+    const versioned = "7" + rand(3);
+    const variantNibble = (8 + Math.floor(Math.random() * 4)).toString(16);
+    const variant = variantNibble + rand(3);
+    return (timeHex.slice(0, 8) +
+        "-" +
+        timeHex.slice(8, 12) +
+        "-" +
+        versioned +
+        "-" +
+        variant +
+        "-" +
+        rand(12));
+}
diff --git a/packages/mcp/build/lib/footnote-canonicalize.js b/packages/mcp/build/lib/footnote-canonicalize.js
new file mode 100644
index 00000000..d2d91400
--- /dev/null
+++ b/packages/mcp/build/lib/footnote-canonicalize.js
@@ -0,0 +1,215 @@
+/**
+ * Server-side footnote canonicalizer (MCP mirror — PURE).
+ *
+ * `canonicalizeFootnotes(doc)` is a pure ProseMirror-JSON port of the editor's
+ * `footnoteSyncPlugin` end-state, identical in behaviour to
+ * `@docmost/editor-ext`'s `canonicalizeFootnotes`. It is mirrored here — rather
+ * than imported from editor-ext — for the SAME reason `footnote-lex.ts` and the
+ * `docmost-schema.ts` nodes are mirrored: the MCP package is deliberately
+ * decoupled from the browser/React-heavy editor barrel and operates on plain
+ * JSON. The editor-ext copy owns the golden test against the live plugin; this
+ * copy must stay behaviourally identical (a SHARED golden corpus, exercised by
+ * both test suites, pins that — see `test/unit/footnote-corpus.mjs`).
+ *
+ * This module is the pure MIRROR only. The inline-authoring helpers
+ * (`footnoteContentKey`, `makeFootnoteDefinition`, `generateFootnoteId`) used by
+ * `insertInlineFootnote` live in the sibling `footnote-authoring.ts`, so this
+ * file is compositionally symmetric to the editor-ext copy.
+ *
+ * Why it exists: every NON-editor write path (markdown import, update_page_json,
+ * docmost_transform, insert_footnote) builds ProseMirror JSON directly, so the
+ * editor's footnote plugins never run and the canonical topology (sequential
+ * numbering by first reference, one trailing list, no orphans, no raw `[^id]`)
+ * was never enforced. Running this at the end of every write path closes that
+ * gap; because it is idempotent, it is a no-op when the footnotes are already
+ * canonical (no spurious mutations / git-sync churn).
+ *
+ * ENFORCEMENT RULE (#228): any NEW FULL-document persist path MUST call
+ * `canonicalizeFootnotes(doc)` before writing — the current callers are
+ * `markdownToProseMirrorCanonical` (page markdown import/update; the plain
+ * `markdownToProseMirror` used for COMMENT bodies must NOT, or it would drop a
+ * reference-less definition), `update_page_json`, `docmost_transform`,
+ * `insert_footnote`, and `copy_page_content`. Append/prepend FRAGMENT writes MUST
+ * NOT canonicalize. This is deliberately per-call-site (the replace-vs-fragment
+ * and comment-vs-page nuances make a single naive wrapper unsafe).
+ */
+const FOOTNOTE_REFERENCE_NAME = "footnoteReference";
+const FOOTNOTES_LIST_NAME = "footnotesList";
+const FOOTNOTE_DEFINITION_NAME = "footnoteDefinition";
+function cloneJson(v) {
+    if (typeof structuredClone === "function")
+        return structuredClone(v);
+    return JSON.parse(JSON.stringify(v));
+}
+function isEmptyParagraph(node) {
+    return (!!node &&
+        node.type === "paragraph" &&
+        (!Array.isArray(node.content) || node.content.length === 0));
+}
+function collectReferenceIds(node, out, seen) {
+    if (!node || typeof node !== "object")
+        return;
+    if (node.type === FOOTNOTE_REFERENCE_NAME) {
+        const id = node?.attrs?.id;
+        if (id && !seen.has(id)) {
+            seen.add(id);
+            out.push(id);
+        }
+    }
+    if (Array.isArray(node.content)) {
+        for (const child of node.content)
+            collectReferenceIds(child, out, seen);
+    }
+}
+function collectDefinitions(node, out) {
+    if (!node || typeof node !== "object")
+        return;
+    if (node.type === FOOTNOTE_DEFINITION_NAME)
+        out.push(node);
+    if (Array.isArray(node.content)) {
+        for (const child of node.content)
+            collectDefinitions(child, out);
+    }
+}
+function emptyDefinition(id) {
+    return {
+        type: FOOTNOTE_DEFINITION_NAME,
+        attrs: { id },
+        content: [{ type: "paragraph" }],
+    };
+}
+/**
+ * Deep equality over plain JSON: arrays are compared POSITIONALLY
+ * (order-SENSITIVE), object keys order-insensitively. The array order-sensitivity
+ * is required for correctness here — a reordered `footnotesList.content` must
+ * compare UNEQUAL so the canonical rebuild fires instead of leaving it in place.
+ */
+function deepEqualJson(a, b) {
+    if (a === b)
+        return true;
+    if (a == null || b == null || typeof a !== typeof b)
+        return false;
+    if (Array.isArray(a) || Array.isArray(b)) {
+        if (!Array.isArray(a) || !Array.isArray(b) || a.length !== b.length) {
+            return false;
+        }
+        for (let i = 0; i < a.length; i++) {
+            if (!deepEqualJson(a[i], b[i]))
+                return false;
+        }
+        return true;
+    }
+    if (typeof a === "object") {
+        const ka = Object.keys(a);
+        const kb = Object.keys(b);
+        if (ka.length !== kb.length)
+            return false;
+        for (const k of ka) {
+            if (!Object.prototype.hasOwnProperty.call(b, k))
+                return false;
+            if (!deepEqualJson(a[k], b[k]))
+                return false;
+        }
+        return true;
+    }
+    return false;
+}
+/**
+ * Canonicalize footnotes in a ProseMirror-JSON document. See the file header and
+ * the editor-ext twin for the full contract. Pure (deep-clones input,
+ * deterministic, idempotent).
+ */
+export function canonicalizeFootnotes(doc) {
+    if (doc == null ||
+        typeof doc !== "object" ||
+        !Array.isArray(doc.content)) {
+        return doc;
+    }
+    const out = cloneJson(doc);
+    // 1) Distinct reference ids in document order (deep — refs can live in
+    //    callouts, tables, list items, ...). The ordering/numbering truth.
+    const referenceIds = [];
+    collectReferenceIds(out, referenceIds, new Set());
+    // 2) Every definition node in document order (deep).
+    const defNodes = [];
+    collectDefinitions(out, defNodes);
+    // 3) First definition per id wins; later duplicates carry the SAME id, so they
+    //    cannot be referenced separately and would be orphans — they are dropped.
+    const defById = new Map();
+    for (const d of defNodes) {
+        const id = d?.attrs?.id;
+        if (id && !defById.has(id))
+            defById.set(id, d);
+    }
+    // 4) Build the ordered definition list: one per referenced id, in REFERENCE
+    //    order, reusing the existing node (shallow-copied, id normalized — `out` is
+    //    already deep-cloned and the old lists are cut) or synthesizing an empty
+    //    one. Definitions whose id is not referenced are orphans and never added.
+    const orderedDefs = [];
+    for (const id of referenceIds) {
+        const existing = defById.get(id);
+        if (existing) {
+            orderedDefs.push({
+                ...existing,
+                attrs: { ...(existing.attrs ?? {}), id },
+            });
+        }
+        else {
+            orderedDefs.push(emptyDefinition(id));
+        }
+    }
+    // 5) No references -> there must be NO list at all (at any depth).
+    if (referenceIds.length === 0) {
+        stripFootnotesListsDeep(out);
+        return out;
+    }
+    // 6) Placement parity with the live plugin: when the document is ALREADY in the
+    //    canonical single-list state, leave that list exactly where it sits rather
+    //    than cutting and re-inserting it at the end (the plugin never repositions a
+    //    sole correct list, so moving it would silently reorder any content that
+    //    follows the list on the first write).
+    const topLevelLists = out.content.filter((n) => n && n.type === FOOTNOTES_LIST_NAME);
+    if (topLevelLists.length === 1 &&
+        defNodes.length === orderedDefs.length &&
+        deepEqualJson(topLevelLists[0].content, orderedDefs)) {
+        return out;
+    }
+    // 7) Otherwise rebuild: strip every footnotesList AND every bare
+    //    footnoteDefinition at ANY depth (collectDefinitions gathers defs
+    //    recursively, so a list nested in a callout/blockquote — or a bare
+    //    definition outside any list — would otherwise have its defs copied into the
+    //    rebuilt list while the original survives in place → duplicates) and
+    //    re-insert exactly one list after the last meaningful (non-empty paragraph)
+    //    top-level block.
+    stripFootnotesListsDeep(out);
+    stripFootnoteDefinitionsDeep(out);
+    const top = out.content;
+    let insertAt = top.length;
+    while (insertAt > 0 && isEmptyParagraph(top[insertAt - 1]))
+        insertAt--;
+    top.splice(insertAt, 0, { type: FOOTNOTES_LIST_NAME, content: orderedDefs });
+    out.content = top;
+    return out;
+}
+/** Remove every `footnotesList` node at ANY depth (mutates the given clone). */
+function stripFootnotesListsDeep(node) {
+    if (!node || typeof node !== "object" || !Array.isArray(node.content))
+        return;
+    node.content = node.content.filter((c) => !(c && c.type === FOOTNOTES_LIST_NAME));
+    for (const child of node.content)
+        stripFootnotesListsDeep(child);
+}
+/**
+ * Remove every BARE `footnoteDefinition` node at ANY depth (mutates the given
+ * clone). Runs only in the rebuild path AFTER the lists are stripped, so it
+ * targets definitions that were sitting outside a list (e.g. hand-authored via a
+ * raw-JSON write path and nested in a callout); their content was already copied
+ * into the rebuilt list, so leaving the originals would duplicate them.
+ */
+function stripFootnoteDefinitionsDeep(node) {
+    if (!node || typeof node !== "object" || !Array.isArray(node.content))
+        return;
+    node.content = node.content.filter((c) => !(c && c.type === FOOTNOTE_DEFINITION_NAME));
+    for (const child of node.content)
+        stripFootnoteDefinitionsDeep(child);
+}
diff --git a/packages/mcp/build/lib/transforms.js b/packages/mcp/build/lib/transforms.js
index 2fc5d37b..c1b822ba 100644
--- a/packages/mcp/build/lib/transforms.js
+++ b/packages/mcp/build/lib/transforms.js
@@ -14,6 +14,9 @@
  *  - `marks` arrays are preserved verbatim when fragments are split/reordered.
  */
 import { blockPlainText } from "./node-ops.js";
+import { canonicalizeFootnotes } from "./footnote-canonicalize.js";
+import { footnoteContentKey, makeFootnoteDefinition, generateFootnoteId, } from "./footnote-authoring.js";
+export { canonicalizeFootnotes } from "./footnote-canonicalize.js";
 /** Deep-clone a JSON-serializable value without mutating the original. */
 function clone(value) {
     if (typeof structuredClone === "function") {
@@ -64,6 +67,36 @@ export function getList(doc, predicate) {
     });
     return found;
 }
+/**
+ * Textblocks that hold raw text but do NOT accept inline atom nodes. A
+ * `footnoteReference` is `group:"inline", atom:true`; `codeBlock` is
+ * `content:"text*"` (text only), so splicing a footnoteReference into it yields
+ * an invalid document. (paragraph/heading/detailsSummary are `inline*` and DO
+ * accept it; footnote definitions live inside a footnotesList which the
+ * footnote inserter excludes via `beforeBlock`.)
+ */
+const INLINE_ATOM_FORBIDDEN_BLOCKS = new Set(["codeBlock"]);
+/**
+ * Footnote-notes subtrees the inline footnote inserter must never split into (at
+ * any depth): a `footnotesList` and the `footnoteDefinition`s it holds. Anchoring
+ * a reference inside one of these would later be dropped as an orphan by the
+ * canonicalizer, taking the existing definition's text with it.
+ */
+const FOOTNOTE_NOTES_SUBTREES = new Set([
+    "footnotesList",
+    "footnoteDefinition",
+]);
+/** True if `node` IS, or contains at any depth, a footnotesList/footnoteDefinition. */
+function containsFootnoteNotes(node) {
+    if (!isObject(node))
+        return false;
+    if (FOOTNOTE_NOTES_SUBTREES.has(node.type))
+        return true;
+    if (Array.isArray(node.content)) {
+        return node.content.some((c) => containsFootnoteNotes(c));
+    }
+    return false;
+}
 /**
  * Insert `marker` as a PLAIN (unmarked) text run right after the first
  * occurrence of `anchor`.
@@ -83,6 +116,19 @@ export function getList(doc, predicate) {
  * false when the anchor text was not found in any in-scope block.
  */
 export function insertMarkerAfter(doc, anchor, marker, opts = {}) {
+    // A plain marker is a leading-space-padded unmarked text run.
+    return insertNodesAfterAnchor(doc, anchor, () => [{ type: "text", text: " " + marker }], opts);
+}
+/**
+ * Mark-safe insertion CORE: split the inline text run that holds the END of
+ * `anchor` (preserving the surrounding marks) and splice the nodes produced by
+ * `makeMiddle()` in at the split point. `insertMarkerAfter` (plain text marker)
+ * and `insertInlineFootnote` (a `footnoteReference` node) are both thin callers —
+ * the only difference is WHAT is inserted (a space-padded text run vs. a node
+ * that should hug the preceding word), which is exactly what `makeMiddle`
+ * decides. Operates on a clone; returns `{ doc, inserted }`.
+ */
+function insertNodesAfterAnchor(doc, anchor, makeMiddle, opts = {}) {
     const out = clone(doc);
     if (!isObject(out) || !Array.isArray(out.content) || !anchor) {
         return { doc: out, inserted: false };
@@ -111,10 +157,25 @@ export function insertMarkerAfter(doc, anchor, marker, opts = {}) {
             if (inserted || !isObject(container) || !Array.isArray(container.content)) {
                 return;
             }
+            // Skip a forbidden subtree entirely (e.g. footnotesList/footnoteDefinition):
+            // never split into it, but keep `offset` aligned for any sibling text after
+            // it within this block.
+            if (opts.skipSubtreeTypes && opts.skipSubtreeTypes.has(container.type)) {
+                offset += blockPlainText(container).length;
+                return;
+            }
             const inline = container.content;
             // Detect whether this array is an inline array (contains text nodes).
             const hasText = inline.some((n) => isObject(n) && n.type === "text");
             if (hasText) {
+                // Refuse a textblock whose content spec cannot hold the inserted nodes
+                // (e.g. a codeBlock for an inline atom). Keep `offset` aligned for any
+                // sibling textblocks in this same block, then bail so the search falls
+                // through to the next candidate block.
+                if (opts.forbidBlockTypes && opts.forbidBlockTypes.has(container.type)) {
+                    offset += blockPlainText(container).length;
+                    return;
+                }
                 for (let i = 0; i < inline.length; i++) {
                     const n = inline[i];
                     const len = isObject(n) ? blockPlainText(n).length : 0;
@@ -136,8 +197,9 @@ export function insertMarkerAfter(doc, anchor, marker, opts = {}) {
                         if (before.length > 0) {
                             parts.push({ ...n, text: before, marks: [...marks] });
                         }
-                        // Marker is a PLAIN run: no marks copied. Leading space separates it.
-                        parts.push({ type: "text", text: " " + marker });
+                        // The inserted nodes are caller-decided (a space-padded marker run,
+                        // or a node that hugs the word). They carry no copied marks.
+                        parts.push(...makeMiddle());
                         if (after.length > 0) {
                             parts.push({ ...n, text: after, marks: [...marks] });
                         }
@@ -227,14 +289,16 @@ export function noteItem(inlineNodes) {
  * Wrap inline ProseMirror nodes in a real footnoteDefinition node keyed by id:
  *   { type:"footnoteDefinition", attrs:{id}, content:[{ type:"paragraph", content }] }
  * (mirrors the editor-ext / docmost-schema FootnoteDefinition node).
+ *
+ * Built on the shared `makeFootnoteDefinition` factory (footnote-authoring.ts);
+ * the only extra is a fresh block id on the inner paragraph (Docmost stamps one,
+ * and the canonicalizer preserves attrs as-is). Single factory, one place to
+ * change the definition shape.
  */
 export function footnoteDefinition(id, inlineNodes) {
-    const content = Array.isArray(inlineNodes) ? clone(inlineNodes) : [];
-    return {
-        type: "footnoteDefinition",
-        attrs: { id },
-        content: [{ type: "paragraph", attrs: { id: freshId() }, content }],
-    };
+    const node = makeFootnoteDefinition(id, inlineNodes);
+    node.content[0].attrs = { id: freshId() };
+    return node;
 }
 /**
  * Replace every `[N]` body marker and `\u0000FN<i>\u0000` comment placeholder in
@@ -471,3 +535,97 @@ export function commentsToFootnotes(doc, comments, opts = {}) {
     const synced = setCalloutRange(working, definitions.length);
     return { doc: synced.doc, consumed };
 }
+/**
+ * AUTHOR-INLINE footnote insertion. The caller supplies WHERE (anchorText) and
+ * WHAT (markdown text); numbering and the bottom list are derived server-side by
+ * `canonicalizeFootnotes`. The caller never sees or edits `footnotesList`, never
+ * assigns a number, and cannot desync — orphans / out-of-order lists / raw
+ * `[^id]` markdown are structurally impossible.
+ *
+ * Content DEDUP (#3 in the issue): if an existing definition has the SAME
+ * normalized content key, its id is REUSED (the new reference points at it: one
+ * number, one definition, several references). Otherwise a fresh uuid id is
+ * minted and a new definition added. Conservative — only an exact content match
+ * merges.
+ *
+ * Mechanics: the `footnoteReference` node is inserted DIRECTLY at the anchor via
+ * the same mark-safe split as `insertMarkerAfter` (the shared
+ * `insertNodesAfterAnchor` core), so it hugs the preceding word with no text
+ * sentinel round-trip. The whole document is then canonicalized.
+ *
+ * Operates on a clone of `doc`. When the anchor is not found, returns the input
+ * unchanged with `inserted:false`.
+ */
+export function insertInlineFootnote(doc, opts) {
+    const inline = mdToInlineNodes(opts.text ?? "");
+    // footnoteContentKey only reads `.content`, so key off the inline array
+    // directly instead of building a throwaway definition node.
+    const key = footnoteContentKey({ content: inline });
+    // Content dedup: reuse an existing definition's id when its key matches.
+    let footnoteId = null;
+    let reused = false;
+    if (key !== "") {
+        walk(doc, (n) => {
+            if (footnoteId == null &&
+                isObject(n) &&
+                n.type === "footnoteDefinition" &&
+                n.attrs &&
+                typeof n.attrs.id === "string" &&
+                n.attrs.id !== "" &&
+                footnoteContentKey(n) === key) {
+                footnoteId = n.attrs.id;
+                reused = true;
+            }
+        });
+    }
+    if (footnoteId == null)
+        footnoteId = generateFootnoteId();
+    // Insert the footnoteReference node directly after the anchor (mark-safe
+    // split); it hugs the preceding word with no leading space. Two guards keep the
+    // inline atom out of the notes section and out of blocks that cannot hold it:
+    //  - beforeBlock bounds the search to the BODY, before the first top-level block
+    //    that IS or CONTAINS (at any depth) a footnotesList/footnoteDefinition — so
+    //    a NESTED list or a bare definition also bounds the search, not just a
+    //    top-level list;
+    //  - skipSubtreeTypes refuses to descend into any footnotesList/footnoteDefinition
+    //    subtree, so a reference is never glued inside an existing definition (which
+    //    the canonicalizer would then drop as an orphan, losing that definition's
+    //    prose); and forbidBlockTypes refuses codeBlocks (an inline atom there is a
+    //    schema-invalid doc; insert_footnote skips validateDocStructure).
+    // When the only anchor match is in such a place, the insert is refused and the
+    // write aborts cleanly (inserted:false) instead of destroying content.
+    const boundaryIdx = Array.isArray(doc?.content)
+        ? doc.content.findIndex((n) => containsFootnoteNotes(n))
+        : -1;
+    const r = insertNodesAfterAnchor(doc, (opts.anchorText ?? "").trimEnd(), () => [{ type: "footnoteReference", attrs: { id: footnoteId } }], {
+        ...(boundaryIdx >= 0 ? { beforeBlock: boundaryIdx } : {}),
+        forbidBlockTypes: INLINE_ATOM_FORBIDDEN_BLOCKS,
+        skipSubtreeTypes: FOOTNOTE_NOTES_SUBTREES,
+    });
+    if (!r.inserted) {
+        return { doc: clone(doc), inserted: false, footnoteId, reused };
+    }
+    let working = r.doc;
+    // Add a NEW definition (canonicalize will order/place it); a reused id needs
+    // no new definition (the existing one is shared).
+    if (!reused) {
+        appendDefinition(working, makeFootnoteDefinition(footnoteId, inline));
+    }
+    // Derive numbering + the single bottom list deterministically.
+    working = canonicalizeFootnotes(working);
+    return { doc: working, inserted: true, footnoteId, reused };
+}
+/**
+ * Append a definition node so the canonicalizer can order/place it: into the
+ * first existing footnotesList, or a new trailing list when none exists.
+ */
+function appendDefinition(doc, defNode) {
+    const existingList = getList(doc, (n) => isObject(n) && n.type === "footnotesList");
+    if (existingList && Array.isArray(existingList.content)) {
+        existingList.content.push(defNode);
+        return;
+    }
+    if (Array.isArray(doc.content)) {
+        doc.content.push({ type: "footnotesList", content: [defNode] });
+    }
+}
diff --git a/packages/mcp/src/client.ts b/packages/mcp/src/client.ts
index 39ff3146..181c7e79 100644
--- a/packages/mcp/src/client.ts
+++ b/packages/mcp/src/client.ts
@@ -17,6 +17,7 @@ import {
   updatePageContentRealtime,
   replacePageContent,
   markdownToProseMirror,
+  markdownToProseMirrorCanonical,
   mutatePageContent,
   buildCollabWsUrl,
   assertYjsEncodable,
@@ -60,6 +61,8 @@ import {
   noteItem,
   mdToInlineNodes,
   commentsToFootnotes,
+  canonicalizeFootnotes,
+  insertInlineFootnote,
 } from "./lib/transforms.js";
 import vm from "node:vm";
 
@@ -1344,10 +1347,16 @@ export class DocmostClient {
     // inject javascript:/data: link hrefs or media srcs straight into the doc.
     this.validateDocUrls(doc);
 
+    // Canonicalize footnotes (idempotent): an agent-authored JSON doc cannot
+    // leave footnotes out of order, orphaned, or in multiple lists — the bottom
+    // list + numbering are always derived from reference order. No-op when the
+    // footnotes are already canonical.
+    doc = canonicalizeFootnotes(doc);
+
     // Write the BODY first, then the title (#159 split-brain): a failed body
     // write (e.g. persist timeout) must not leave a new title over the old body.
     const collabToken = await this.getCollabTokenWithReauth();
-    const mutation = await replacePageContent(
+    const mutation = await this.replacePage(
       pageId,
       doc,
       collabToken,
@@ -1368,6 +1377,95 @@ export class DocmostClient {
     };
   }
 
+  /**
+   * AUTHOR-INLINE footnote insertion. The agent supplies only WHERE
+   * (`anchorText`, a snippet of body text to attach the marker after) and WHAT
+   * (`text`, the footnote content as markdown). Numbering and the bottom
+   * `footnotesList` are derived deterministically server-side
+   * (`insertInlineFootnote` -> `canonicalizeFootnotes`): the agent never sees,
+   * assigns, or edits a footnote number or the list, so it CANNOT desync.
+   *
+   * Content DEDUP: when an existing definition has the same content, its id is
+   * reused (one number, one definition, several references). The write is atomic
+   * via `mutatePageContent` (single-writer, page-locked); if the anchor text is
+   * not found the transform aborts with a clear error and no write happens.
+   */
+  async insertFootnote(pageId: string, anchorText: string, text: string) {
+    await this.ensureAuthenticated();
+    if (!anchorText || !anchorText.trim()) {
+      throw new Error("insert_footnote: anchorText is required");
+    }
+    if (text == null || `${text}`.trim() === "") {
+      throw new Error("insert_footnote: text is required");
+    }
+    const collabToken = await this.getCollabTokenWithReauth();
+    let result: { footnoteId: string; reused: boolean } | null = null;
+    const mutation = await this.mutatePage(
+      pageId,
+      collabToken,
+      this.apiUrl,
+      (liveDoc: any) => {
+        const r = insertInlineFootnote(liveDoc, { anchorText, text });
+        if (!r.inserted) {
+          // Abort the page-locked write by throwing: mutatePageContent does not
+          // persist when the transform throws, so a missing anchor leaves the
+          // page untouched (no partial write).
+          throw new Error(
+            `insert_footnote: anchor text not found: ${JSON.stringify(
+              anchorText.slice(0, 80),
+            )}`,
+          );
+        }
+        result = { footnoteId: r.footnoteId, reused: r.reused };
+        return r.doc;
+      },
+    );
+    // The not-found path throws inside the transform (aborting mutatePage), so by
+    // here `result` is always set.
+    const r = result!;
+    return {
+      success: true,
+      modified: true,
+      pageId,
+      footnoteId: r.footnoteId,
+      reused: r.reused,
+      message: r.reused
+        ? "Footnote inserted (reused an existing same-content definition)."
+        : "Footnote inserted.",
+      verify: mutation.verify,
+    };
+  }
+
+  /**
+   * Page-locked write seam over collaboration.mutatePageContent. Production just
+   * delegates; it exists as an overridable method so the insert_footnote wrapper
+   * (transform abort-on-not-found + response shaping) can be unit-tested without
+   * standing up a live Hocuspocus collab socket.
+   */
+  protected mutatePage(
+    pageId: string,
+    collabToken: string,
+    apiUrl: string,
+    transform: (doc: any) => any,
+  ): Promise<{ doc?: any; verify?: any }> {
+    return mutatePageContent(pageId, collabToken, apiUrl, transform);
+  }
+
+  /**
+   * Full-document write seam over collaboration.replacePageContent. Production
+   * just delegates; it exists as an overridable method so the full-doc write
+   * tools (update_page_json, copy_page_content) can have their footnote-
+   * canonicalization binding unit-tested without a live Hocuspocus collab socket.
+   */
+  protected replacePage(
+    pageId: string,
+    doc: any,
+    collabToken: string,
+    apiUrl: string,
+  ): Promise<{ doc?: any; verify?: any }> {
+    return replacePageContent(pageId, doc, collabToken, apiUrl);
+  }
+
   /**
    * Export a page to a single self-contained Docmost-flavoured markdown file:
    * meta block + body (with inline comment anchors + diagrams) + comment
@@ -1408,7 +1506,8 @@ export class DocmostClient {
   async importPageMarkdown(pageId: string, fullMarkdown: string): Promise<any> {
     await this.ensureAuthenticated();
     const { meta, body, comments } = parseDocmostMarkdown(fullMarkdown);
-    const doc = await markdownToProseMirror(body);
+    // PAGE import: canonicalize footnotes (see markdownToProseMirrorCanonical).
+    const doc = await markdownToProseMirrorCanonical(body);
     const collabToken = await this.getCollabTokenWithReauth();
     const mutation = await replacePageContent(
       pageId,
@@ -1503,10 +1602,16 @@ export class DocmostClient {
     // (parity with updatePageJson; harmless for already-stored source content).
     this.validateDocUrls(content);
 
+    // Defense-in-depth (#228): this is a FULL-document write, so canonicalize
+    // footnotes before copying — a no-op on already-canonical source content, but
+    // it guarantees a copy can never propagate a non-canonical footnote topology
+    // to the target (parity with the other full-doc write paths).
+    const canonical = canonicalizeFootnotes(content);
+
     const collabToken = await this.getCollabTokenWithReauth();
-    const mutation = await replacePageContent(
+    const mutation = await this.replacePage(
       targetPageId,
-      content,
+      canonical,
       collabToken,
       this.apiUrl,
     );
@@ -1515,7 +1620,7 @@ export class DocmostClient {
       success: true,
       sourcePageId,
       targetPageId,
-      copiedNodes: content.content.length,
+      copiedNodes: canonical.content.length,
       verify: mutation.verify,
     };
   }
@@ -2033,7 +2138,10 @@ export class DocmostClient {
       }
     }
 
-    // Convert through the full Docmost schema (consistent with page paths)
+    // Convert through the full Docmost schema. Deliberately the NON-canonicalizing
+    // variant: a comment body may carry a footnote definition with no matching
+    // reference, and canonicalization would drop it (data loss). See
+    // markdownToProseMirror vs markdownToProseMirrorCanonical.
     const jsonContent = await markdownToProseMirror(content);
     const payload: Record<string, any> = {
       pageId,
@@ -2136,6 +2244,7 @@ export class DocmostClient {
 
   async updateComment(commentId: string, content: string) {
     await this.ensureAuthenticated();
+    // NON-canonicalizing on purpose (comment body — see createComment).
     const jsonContent = await markdownToProseMirror(content);
     await this.client.post("/comments/update", {
       commentId,
@@ -2986,6 +3095,8 @@ export class DocmostClient {
         noteItem,
         mdToInlineNodes,
         commentsToFootnotes,
+        canonicalizeFootnotes,
+        insertInlineFootnote,
       },
     };
 
@@ -3022,24 +3133,33 @@ export class DocmostClient {
           "transform must evaluate to a function (doc, ctx) => doc",
         );
       }
-      const result = vm.runInNewContext(
+      const raw = vm.runInNewContext(
         "f(d, c)",
         { f: fn, d: sandbox.doc, c: ctx },
         { timeout: 5000 },
       );
       if (
-        !result ||
-        typeof result !== "object" ||
-        result.type !== "doc" ||
-        !Array.isArray(result.content)
+        !raw ||
+        typeof raw !== "object" ||
+        raw.type !== "doc" ||
+        !Array.isArray(raw.content)
       ) {
         throw new Error(
           'transform must return a ProseMirror doc node ({ type:"doc", content:[...] })',
         );
       }
-      // Validate the returned doc before it can be written.
-      this.validateDocStructure(result);
-      this.validateDocUrls(result);
+      // Validate the RAW transform output FIRST (structure — including the
+      // MAX_DEPTH guard — and URLs), mirroring updatePageJson. The canonicalizer
+      // recurses without a depth limiter, so validating after it would turn a
+      // too-deep doc into an opaque "Maximum call stack size exceeded" instead of
+      // the intended "nesting exceeds the maximum depth" error.
+      this.validateDocStructure(raw);
+      this.validateDocUrls(raw);
+      // Auto-canonicalize footnotes after the transform (idempotent): no write
+      // path can leave footnotes out of order / orphaned / in a raw `[^id]`
+      // block. In a dryRun preview this may surface footnote edits the script
+      // author did not write (the canonicalizer tidied them) — that is expected.
+      const result = canonicalizeFootnotes(raw);
       newDoc = result;
       return result;
     };
diff --git a/packages/mcp/src/index.ts b/packages/mcp/src/index.ts
index 51d1489b..db29f143 100644
--- a/packages/mcp/src/index.ts
+++ b/packages/mcp/src/index.ts
@@ -892,8 +892,15 @@ server.registerTool(
       "mark-safe), setCalloutRange(doc, n) (sync a [1]…[K] callout range to " +
       "[1]…[n]), noteItem(inlineNodes) (wrap inline nodes in a listItem with a " +
       "fresh id), mdToInlineNodes(markdown) (comment markdown -> inline nodes), " +
-      "and commentsToFootnotes(doc, comments, {notesHeading}) (turn inline " +
-      "comments into numbered footnotes). Footnote convention: markers are " +
+      "commentsToFootnotes(doc, comments, {notesHeading}) (turn inline " +
+      "comments into numbered footnotes), canonicalizeFootnotes(doc) (derive " +
+      "footnote numbering + the single bottom list from reference order, drop " +
+      "orphans/duplicates — runs AUTOMATICALLY on the transform RESULT, so the " +
+      "applied (and dryRun-previewed) doc is always footnote-canonical; a dryRun " +
+      "diff may therefore show footnote tidy-ups your script did not make, and " +
+      "it is idempotent after the first run), and " +
+      "insertInlineFootnote(doc, {anchorText, text}) (author-inline footnote: " +
+      "marker + dedup'd definition, list derived). Footnote convention: markers are " +
       "plain '[N]' text in the body; the notes are an orderedList under a " +
       "heading whose text is 'Примечания переводчика'. The transform runs " +
       "sandboxed (no require/process/fs/network, 5s timeout) and must return a " +
@@ -908,7 +915,8 @@ server.registerTool(
             "parenthesized function). It receives a clone of the live doc and " +
             "ctx (comments, log, consume(id), helpers: blockText/walk/getList/" +
             "insertMarkerAfter/setCalloutRange/noteItem/mdToInlineNodes/" +
-            "commentsToFootnotes) and must return a {type:'doc'} node.",
+            "commentsToFootnotes/canonicalizeFootnotes/insertInlineFootnote) " +
+            "and must return a {type:'doc'} node.",
         ),
       dryRun: z
         .boolean()
@@ -934,6 +942,41 @@ server.registerTool(
   },
 );
 
+// Tool: insert_footnote
+server.registerTool(
+  "insert_footnote",
+  {
+    description:
+      "Insert an AUTHOR-INLINE footnote: you specify only WHERE (anchorText) " +
+      "and WHAT (text). The footnote marker is placed right after anchorText in " +
+      "the body, and the bottom footnotes list + the numbering are derived " +
+      "deterministically server-side. You do NOT assign a number, and you " +
+      "never see or edit the footnotes list — so footnotes cannot end up out " +
+      "of order, orphaned, or as a raw '[^id]' block. If a footnote with the " +
+      "SAME text already exists, its number is REUSED (one definition, several " +
+      "references). The write is atomic and won't clobber concurrent edits; if " +
+      "anchorText is not found, nothing is written and an error is returned.",
+    inputSchema: {
+      pageId: z.string().min(1),
+      anchorText: z
+        .string()
+        .min(1)
+        .describe(
+          "A snippet of existing body text; the footnote marker is inserted " +
+            "immediately after its first occurrence (mark-safe).",
+        ),
+      text: z
+        .string()
+        .min(1)
+        .describe("The footnote content as markdown (becomes the definition)."),
+    },
+  },
+  async ({ pageId, anchorText, text }) => {
+    const result = await docmostClient.insertFootnote(pageId, anchorText, text);
+    return jsonContent(result);
+  },
+);
+
 // Tool: diff_page_versions
 registerShared(
   SHARED_TOOL_SPECS.diffPageVersions,
diff --git a/packages/mcp/src/lib/collaboration.ts b/packages/mcp/src/lib/collaboration.ts
index aec82aa1..c8b1cf40 100644
--- a/packages/mcp/src/lib/collaboration.ts
+++ b/packages/mcp/src/lib/collaboration.ts
@@ -11,6 +11,7 @@ import { docmostExtensions, docmostSchema } from "./docmost-schema.js";
 import { withPageLock } from "./page-lock.js";
 import { sanitizeForYjs, findUnstorableAttr } from "./node-ops.js";
 import { lexFootnoteLines } from "./footnote-lex.js";
+import { canonicalizeFootnotes } from "./footnote-canonicalize.js";
 import { summarizeChange, VerifyReport } from "./diff.js";
 
 /**
@@ -392,7 +393,20 @@ function extractFootnotes(markdown: string): {
   };
 }
 
-/** Convert markdown to a ProseMirror doc using the full Docmost schema. */
+/**
+ * Convert markdown to a ProseMirror doc using the full Docmost schema.
+ *
+ * This conversion does NOT canonicalize footnotes — it is the shared, content-
+ * preserving primitive used by BOTH page write paths and COMMENT bodies
+ * (createComment / updateComment). Canonicalization MUST NOT run on a comment
+ * body: a comment may legitimately contain a footnote-definition line
+ * (`[^1]: text`) with no matching reference, and the canonicalizer drops a
+ * reference-less footnotesList — which would silently delete the comment's text.
+ *
+ * Page write paths that DO need the canonical footnote topology call
+ * `markdownToProseMirrorCanonical` instead (markdown import, update_page markdown
+ * path). Keep this function reference-loss-free.
+ */
 export async function markdownToProseMirror(
   markdownContent: string,
 ): Promise<any> {
@@ -403,6 +417,23 @@ export async function markdownToProseMirror(
   return generateJSON(bridged, docmostExtensions);
 }
 
+/**
+ * Page-write variant of `markdownToProseMirror`: converts markdown then enforces
+ * the canonical footnote topology. The footnote `section` markdown is emitted in
+ * DEFINITION order, but numbering derives from REFERENCE order, so without this
+ * the bottom list renders out of order (`1, 4, 2, 3, …`); orphan definitions and
+ * duplicate lists are also normalized. Idempotent — a no-op once canonical, and a
+ * no-op for footnote-free content.
+ *
+ * Use this ONLY for full-document PAGE writes (never for comment bodies, where it
+ * would drop a reference-less footnote definition — see `markdownToProseMirror`).
+ */
+export async function markdownToProseMirrorCanonical(
+  markdownContent: string,
+): Promise<any> {
+  return canonicalizeFootnotes(await markdownToProseMirror(markdownContent));
+}
+
 /**
  * Build the collaboration WebSocket URL from an API base URL:
  * switch http(s)->ws(s), strip a trailing /api, mount on /collab.
@@ -801,7 +832,9 @@ export async function updatePageContentRealtime(
   collabToken: string,
   baseUrl: string,
 ): Promise<MutationResult> {
-  const tiptapJson = await markdownToProseMirror(markdownContent);
+  // PAGE write: canonicalize footnotes (markdown import builds the bottom list in
+  // definition order; numbering is reference-ordered).
+  const tiptapJson = await markdownToProseMirrorCanonical(markdownContent);
   return await mutatePageContent(
     pageId,
     collabToken,
diff --git a/packages/mcp/src/lib/footnote-authoring.ts b/packages/mcp/src/lib/footnote-authoring.ts
new file mode 100644
index 00000000..9dfcd7fa
--- /dev/null
+++ b/packages/mcp/src/lib/footnote-authoring.ts
@@ -0,0 +1,91 @@
+/**
+ * Inline-authoring helpers for footnotes (MCP).
+ *
+ * These build/identify footnote DEFINITION nodes for the author-inline tool
+ * (`insertInlineFootnote` in transforms.ts): a content key to de-duplicate notes
+ * by text, a definition-node factory, and a fresh uuidv7-style id generator.
+ *
+ * Split out of `footnote-canonicalize.ts` so that module stays a pure MIRROR of
+ * the editor-ext canonicalizer (compositionally symmetric to the editor-ext
+ * copy, which keeps its authoring helpers in `footnote-util.ts`). The pure
+ * canonicalizer has no dependency on these.
+ */
+
+const FOOTNOTE_DEFINITION_NAME = "footnoteDefinition";
+
+function cloneJson<T>(v: T): T {
+  if (typeof structuredClone === "function") return structuredClone(v);
+  return JSON.parse(JSON.stringify(v)) as T;
+}
+
+/**
+ * Normalized content key for de-duplicating footnote DEFINITIONS by their text.
+ *
+ * Two definitions with the same key are the SAME footnote — so the inline
+ * authoring tool reuses one id (one number, one definition, several references)
+ * instead of minting a second definition. Key = plaintext (whitespace-collapsed,
+ * trimmed) PLUS a signature of the inline mark types in order, so two notes that
+ * read the same but differ in formatting (one bold, one plain) are NOT merged.
+ * Conservative: only an exact match merges.
+ */
+export function footnoteContentKey(defNode: any): string {
+  const parts: string[] = [];
+  const visit = (n: any): void => {
+    if (!n || typeof n !== "object") return;
+    if (n.type === "text" && typeof n.text === "string") {
+      const marks = Array.isArray(n.marks)
+        ? n.marks.map((m: any) => m?.type).filter(Boolean).sort().join(",")
+        : "";
+      parts.push(`${n.text}${marks}`);
+    }
+    if (Array.isArray(n.content)) for (const c of n.content) visit(c);
+  };
+  visit(defNode);
+  // Collapse the assembled text's whitespace and trim, keeping the mark
+  // signature attached so formatting differences still distinguish notes.
+  return parts
+    .join("")
+    .replace(/[ \t\r\n]+/g, " ")
+    .trim();
+}
+
+/**
+ * Build a footnoteDefinition node from inline ProseMirror nodes, keyed by id.
+ */
+export function makeFootnoteDefinition(id: string, inlineNodes: any[]): any {
+  const content = Array.isArray(inlineNodes) ? cloneJson(inlineNodes) : [];
+  return {
+    type: FOOTNOTE_DEFINITION_NAME,
+    attrs: { id },
+    content: [{ type: "paragraph", content }],
+  };
+}
+
+/**
+ * Generate a uuidv7-style id (time-ordered), matching editor-ext's
+ * `generateFootnoteId`. Used for a genuinely-new inline footnote id.
+ */
+export function generateFootnoteId(): string {
+  const now = Date.now();
+  const timeHex = now.toString(16).padStart(12, "0");
+  const rand = (length: number) => {
+    let s = "";
+    for (let i = 0; i < length; i++)
+      s += Math.floor(Math.random() * 16).toString(16);
+    return s;
+  };
+  const versioned = "7" + rand(3);
+  const variantNibble = (8 + Math.floor(Math.random() * 4)).toString(16);
+  const variant = variantNibble + rand(3);
+  return (
+    timeHex.slice(0, 8) +
+    "-" +
+    timeHex.slice(8, 12) +
+    "-" +
+    versioned +
+    "-" +
+    variant +
+    "-" +
+    rand(12)
+  );
+}
diff --git a/packages/mcp/src/lib/footnote-canonicalize.ts b/packages/mcp/src/lib/footnote-canonicalize.ts
new file mode 100644
index 00000000..c83d41e4
--- /dev/null
+++ b/packages/mcp/src/lib/footnote-canonicalize.ts
@@ -0,0 +1,225 @@
+/**
+ * Server-side footnote canonicalizer (MCP mirror — PURE).
+ *
+ * `canonicalizeFootnotes(doc)` is a pure ProseMirror-JSON port of the editor's
+ * `footnoteSyncPlugin` end-state, identical in behaviour to
+ * `@docmost/editor-ext`'s `canonicalizeFootnotes`. It is mirrored here — rather
+ * than imported from editor-ext — for the SAME reason `footnote-lex.ts` and the
+ * `docmost-schema.ts` nodes are mirrored: the MCP package is deliberately
+ * decoupled from the browser/React-heavy editor barrel and operates on plain
+ * JSON. The editor-ext copy owns the golden test against the live plugin; this
+ * copy must stay behaviourally identical (a SHARED golden corpus, exercised by
+ * both test suites, pins that — see `test/unit/footnote-corpus.mjs`).
+ *
+ * This module is the pure MIRROR only. The inline-authoring helpers
+ * (`footnoteContentKey`, `makeFootnoteDefinition`, `generateFootnoteId`) used by
+ * `insertInlineFootnote` live in the sibling `footnote-authoring.ts`, so this
+ * file is compositionally symmetric to the editor-ext copy.
+ *
+ * Why it exists: every NON-editor write path (markdown import, update_page_json,
+ * docmost_transform, insert_footnote) builds ProseMirror JSON directly, so the
+ * editor's footnote plugins never run and the canonical topology (sequential
+ * numbering by first reference, one trailing list, no orphans, no raw `[^id]`)
+ * was never enforced. Running this at the end of every write path closes that
+ * gap; because it is idempotent, it is a no-op when the footnotes are already
+ * canonical (no spurious mutations / git-sync churn).
+ *
+ * ENFORCEMENT RULE (#228): any NEW FULL-document persist path MUST call
+ * `canonicalizeFootnotes(doc)` before writing — the current callers are
+ * `markdownToProseMirrorCanonical` (page markdown import/update; the plain
+ * `markdownToProseMirror` used for COMMENT bodies must NOT, or it would drop a
+ * reference-less definition), `update_page_json`, `docmost_transform`,
+ * `insert_footnote`, and `copy_page_content`. Append/prepend FRAGMENT writes MUST
+ * NOT canonicalize. This is deliberately per-call-site (the replace-vs-fragment
+ * and comment-vs-page nuances make a single naive wrapper unsafe).
+ */
+
+const FOOTNOTE_REFERENCE_NAME = "footnoteReference";
+const FOOTNOTES_LIST_NAME = "footnotesList";
+const FOOTNOTE_DEFINITION_NAME = "footnoteDefinition";
+
+function cloneJson<T>(v: T): T {
+  if (typeof structuredClone === "function") return structuredClone(v);
+  return JSON.parse(JSON.stringify(v)) as T;
+}
+
+function isEmptyParagraph(node: any): boolean {
+  return (
+    !!node &&
+    node.type === "paragraph" &&
+    (!Array.isArray(node.content) || node.content.length === 0)
+  );
+}
+
+function collectReferenceIds(node: any, out: string[], seen: Set<string>): void {
+  if (!node || typeof node !== "object") return;
+  if (node.type === FOOTNOTE_REFERENCE_NAME) {
+    const id = node?.attrs?.id;
+    if (id && !seen.has(id)) {
+      seen.add(id);
+      out.push(id);
+    }
+  }
+  if (Array.isArray(node.content)) {
+    for (const child of node.content) collectReferenceIds(child, out, seen);
+  }
+}
+
+function collectDefinitions(node: any, out: any[]): void {
+  if (!node || typeof node !== "object") return;
+  if (node.type === FOOTNOTE_DEFINITION_NAME) out.push(node);
+  if (Array.isArray(node.content)) {
+    for (const child of node.content) collectDefinitions(child, out);
+  }
+}
+
+function emptyDefinition(id: string): any {
+  return {
+    type: FOOTNOTE_DEFINITION_NAME,
+    attrs: { id },
+    content: [{ type: "paragraph" }],
+  };
+}
+
+/**
+ * Deep equality over plain JSON: arrays are compared POSITIONALLY
+ * (order-SENSITIVE), object keys order-insensitively. The array order-sensitivity
+ * is required for correctness here — a reordered `footnotesList.content` must
+ * compare UNEQUAL so the canonical rebuild fires instead of leaving it in place.
+ */
+function deepEqualJson(a: any, b: any): boolean {
+  if (a === b) return true;
+  if (a == null || b == null || typeof a !== typeof b) return false;
+  if (Array.isArray(a) || Array.isArray(b)) {
+    if (!Array.isArray(a) || !Array.isArray(b) || a.length !== b.length) {
+      return false;
+    }
+    for (let i = 0; i < a.length; i++) {
+      if (!deepEqualJson(a[i], b[i])) return false;
+    }
+    return true;
+  }
+  if (typeof a === "object") {
+    const ka = Object.keys(a);
+    const kb = Object.keys(b);
+    if (ka.length !== kb.length) return false;
+    for (const k of ka) {
+      if (!Object.prototype.hasOwnProperty.call(b, k)) return false;
+      if (!deepEqualJson(a[k], b[k])) return false;
+    }
+    return true;
+  }
+  return false;
+}
+
+/**
+ * Canonicalize footnotes in a ProseMirror-JSON document. See the file header and
+ * the editor-ext twin for the full contract. Pure (deep-clones input,
+ * deterministic, idempotent).
+ */
+export function canonicalizeFootnotes<T = any>(doc: T): T {
+  if (
+    doc == null ||
+    typeof doc !== "object" ||
+    !Array.isArray((doc as any).content)
+  ) {
+    return doc;
+  }
+  const out = cloneJson(doc) as any;
+
+  // 1) Distinct reference ids in document order (deep — refs can live in
+  //    callouts, tables, list items, ...). The ordering/numbering truth.
+  const referenceIds: string[] = [];
+  collectReferenceIds(out, referenceIds, new Set<string>());
+
+  // 2) Every definition node in document order (deep).
+  const defNodes: any[] = [];
+  collectDefinitions(out, defNodes);
+
+  // 3) First definition per id wins; later duplicates carry the SAME id, so they
+  //    cannot be referenced separately and would be orphans — they are dropped.
+  const defById = new Map<string, any>();
+  for (const d of defNodes) {
+    const id = d?.attrs?.id;
+    if (id && !defById.has(id)) defById.set(id, d);
+  }
+
+  // 4) Build the ordered definition list: one per referenced id, in REFERENCE
+  //    order, reusing the existing node (shallow-copied, id normalized — `out` is
+  //    already deep-cloned and the old lists are cut) or synthesizing an empty
+  //    one. Definitions whose id is not referenced are orphans and never added.
+  const orderedDefs: any[] = [];
+  for (const id of referenceIds) {
+    const existing = defById.get(id);
+    if (existing) {
+      orderedDefs.push({
+        ...existing,
+        attrs: { ...(existing.attrs ?? {}), id },
+      });
+    } else {
+      orderedDefs.push(emptyDefinition(id));
+    }
+  }
+
+  // 5) No references -> there must be NO list at all (at any depth).
+  if (referenceIds.length === 0) {
+    stripFootnotesListsDeep(out);
+    return out;
+  }
+
+  // 6) Placement parity with the live plugin: when the document is ALREADY in the
+  //    canonical single-list state, leave that list exactly where it sits rather
+  //    than cutting and re-inserting it at the end (the plugin never repositions a
+  //    sole correct list, so moving it would silently reorder any content that
+  //    follows the list on the first write).
+  const topLevelLists = out.content.filter(
+    (n: any) => n && n.type === FOOTNOTES_LIST_NAME,
+  );
+  if (
+    topLevelLists.length === 1 &&
+    defNodes.length === orderedDefs.length &&
+    deepEqualJson(topLevelLists[0].content, orderedDefs)
+  ) {
+    return out;
+  }
+
+  // 7) Otherwise rebuild: strip every footnotesList AND every bare
+  //    footnoteDefinition at ANY depth (collectDefinitions gathers defs
+  //    recursively, so a list nested in a callout/blockquote — or a bare
+  //    definition outside any list — would otherwise have its defs copied into the
+  //    rebuilt list while the original survives in place → duplicates) and
+  //    re-insert exactly one list after the last meaningful (non-empty paragraph)
+  //    top-level block.
+  stripFootnotesListsDeep(out);
+  stripFootnoteDefinitionsDeep(out);
+  const top: any[] = out.content;
+  let insertAt = top.length;
+  while (insertAt > 0 && isEmptyParagraph(top[insertAt - 1])) insertAt--;
+  top.splice(insertAt, 0, { type: FOOTNOTES_LIST_NAME, content: orderedDefs });
+  out.content = top;
+  return out;
+}
+
+/** Remove every `footnotesList` node at ANY depth (mutates the given clone). */
+function stripFootnotesListsDeep(node: any): void {
+  if (!node || typeof node !== "object" || !Array.isArray(node.content)) return;
+  node.content = node.content.filter(
+    (c: any) => !(c && c.type === FOOTNOTES_LIST_NAME),
+  );
+  for (const child of node.content) stripFootnotesListsDeep(child);
+}
+
+/**
+ * Remove every BARE `footnoteDefinition` node at ANY depth (mutates the given
+ * clone). Runs only in the rebuild path AFTER the lists are stripped, so it
+ * targets definitions that were sitting outside a list (e.g. hand-authored via a
+ * raw-JSON write path and nested in a callout); their content was already copied
+ * into the rebuilt list, so leaving the originals would duplicate them.
+ */
+function stripFootnoteDefinitionsDeep(node: any): void {
+  if (!node || typeof node !== "object" || !Array.isArray(node.content)) return;
+  node.content = node.content.filter(
+    (c: any) => !(c && c.type === FOOTNOTE_DEFINITION_NAME),
+  );
+  for (const child of node.content) stripFootnoteDefinitionsDeep(child);
+}
diff --git a/packages/mcp/src/lib/transforms.ts b/packages/mcp/src/lib/transforms.ts
index 98269aff..e3ab0cff 100644
--- a/packages/mcp/src/lib/transforms.ts
+++ b/packages/mcp/src/lib/transforms.ts
@@ -15,6 +15,14 @@
  */
 
 import { blockPlainText } from "./node-ops.js";
+import { canonicalizeFootnotes } from "./footnote-canonicalize.js";
+import {
+  footnoteContentKey,
+  makeFootnoteDefinition,
+  generateFootnoteId,
+} from "./footnote-authoring.js";
+
+export { canonicalizeFootnotes } from "./footnote-canonicalize.js";
 
 /** Deep-clone a JSON-serializable value without mutating the original. */
 function clone<T>(value: T): T {
@@ -73,13 +81,61 @@ export function getList(
   return found;
 }
 
-/** Options for insertMarkerAfter. */
+/** Options for insertMarkerAfter / insertNodesAfterAnchor. */
 export interface InsertMarkerOptions {
   /**
    * Limit the search to TOP-LEVEL blocks with index < beforeBlock. Used to keep
    * footnote markers in the body and out of the notes section.
    */
   beforeBlock?: number;
+  /**
+   * Textblock node types that MUST NOT receive the inserted nodes. When the
+   * split point lands inside such a block it is refused (skipped), so an inline
+   * ATOM (e.g. footnoteReference) is never spliced into a block whose content
+   * spec forbids it — which would persist a schema-invalid doc. Plain-text
+   * markers leave this unset (text is valid inside a codeBlock).
+   */
+  forbidBlockTypes?: ReadonlySet<string>;
+  /**
+   * Node types whose ENTIRE subtree is skipped during the walk (never split into,
+   * at any depth). Used to keep the footnote inserter out of the notes section:
+   * splitting text inside an existing `footnoteDefinition` would glue a reference
+   * into a definition, which the canonicalizer then drops as an orphan together
+   * with the definition's prose — silent loss of an existing footnote. Skipped
+   * subtrees still advance the running offset so sibling text stays aligned.
+   */
+  skipSubtreeTypes?: ReadonlySet<string>;
+}
+
+/**
+ * Textblocks that hold raw text but do NOT accept inline atom nodes. A
+ * `footnoteReference` is `group:"inline", atom:true`; `codeBlock` is
+ * `content:"text*"` (text only), so splicing a footnoteReference into it yields
+ * an invalid document. (paragraph/heading/detailsSummary are `inline*` and DO
+ * accept it; footnote definitions live inside a footnotesList which the
+ * footnote inserter excludes via `beforeBlock`.)
+ */
+const INLINE_ATOM_FORBIDDEN_BLOCKS: ReadonlySet<string> = new Set(["codeBlock"]);
+
+/**
+ * Footnote-notes subtrees the inline footnote inserter must never split into (at
+ * any depth): a `footnotesList` and the `footnoteDefinition`s it holds. Anchoring
+ * a reference inside one of these would later be dropped as an orphan by the
+ * canonicalizer, taking the existing definition's text with it.
+ */
+const FOOTNOTE_NOTES_SUBTREES: ReadonlySet<string> = new Set([
+  "footnotesList",
+  "footnoteDefinition",
+]);
+
+/** True if `node` IS, or contains at any depth, a footnotesList/footnoteDefinition. */
+function containsFootnoteNotes(node: any): boolean {
+  if (!isObject(node)) return false;
+  if (FOOTNOTE_NOTES_SUBTREES.has(node.type)) return true;
+  if (Array.isArray(node.content)) {
+    return node.content.some((c: any) => containsFootnoteNotes(c));
+  }
+  return false;
 }
 
 /**
@@ -105,6 +161,30 @@ export function insertMarkerAfter(
   anchor: string,
   marker: string,
   opts: InsertMarkerOptions = {},
+): { doc: any; inserted: boolean } {
+  // A plain marker is a leading-space-padded unmarked text run.
+  return insertNodesAfterAnchor(
+    doc,
+    anchor,
+    () => [{ type: "text", text: " " + marker }],
+    opts,
+  );
+}
+
+/**
+ * Mark-safe insertion CORE: split the inline text run that holds the END of
+ * `anchor` (preserving the surrounding marks) and splice the nodes produced by
+ * `makeMiddle()` in at the split point. `insertMarkerAfter` (plain text marker)
+ * and `insertInlineFootnote` (a `footnoteReference` node) are both thin callers —
+ * the only difference is WHAT is inserted (a space-padded text run vs. a node
+ * that should hug the preceding word), which is exactly what `makeMiddle`
+ * decides. Operates on a clone; returns `{ doc, inserted }`.
+ */
+function insertNodesAfterAnchor(
+  doc: any,
+  anchor: string,
+  makeMiddle: () => any[],
+  opts: InsertMarkerOptions = {},
 ): { doc: any; inserted: boolean } {
   const out = clone(doc);
   if (!isObject(out) || !Array.isArray(out.content) || !anchor) {
@@ -137,12 +217,27 @@ export function insertMarkerAfter(
       if (inserted || !isObject(container) || !Array.isArray(container.content)) {
         return;
       }
+      // Skip a forbidden subtree entirely (e.g. footnotesList/footnoteDefinition):
+      // never split into it, but keep `offset` aligned for any sibling text after
+      // it within this block.
+      if (opts.skipSubtreeTypes && opts.skipSubtreeTypes.has(container.type)) {
+        offset += blockPlainText(container).length;
+        return;
+      }
       const inline = container.content;
       // Detect whether this array is an inline array (contains text nodes).
       const hasText = inline.some(
         (n: any) => isObject(n) && n.type === "text",
       );
       if (hasText) {
+        // Refuse a textblock whose content spec cannot hold the inserted nodes
+        // (e.g. a codeBlock for an inline atom). Keep `offset` aligned for any
+        // sibling textblocks in this same block, then bail so the search falls
+        // through to the next candidate block.
+        if (opts.forbidBlockTypes && opts.forbidBlockTypes.has(container.type)) {
+          offset += blockPlainText(container).length;
+          return;
+        }
         for (let i = 0; i < inline.length; i++) {
           const n = inline[i];
           const len = isObject(n) ? blockPlainText(n).length : 0;
@@ -166,8 +261,9 @@ export function insertMarkerAfter(
             if (before.length > 0) {
               parts.push({ ...n, text: before, marks: [...marks] });
             }
-            // Marker is a PLAIN run: no marks copied. Leading space separates it.
-            parts.push({ type: "text", text: " " + marker });
+            // The inserted nodes are caller-decided (a space-padded marker run,
+            // or a node that hugs the word). They carry no copied marks.
+            parts.push(...makeMiddle());
             if (after.length > 0) {
               parts.push({ ...n, text: after, marks: [...marks] });
             }
@@ -268,14 +364,16 @@ export function noteItem(inlineNodes: any[]): any {
  * Wrap inline ProseMirror nodes in a real footnoteDefinition node keyed by id:
  *   { type:"footnoteDefinition", attrs:{id}, content:[{ type:"paragraph", content }] }
  * (mirrors the editor-ext / docmost-schema FootnoteDefinition node).
+ *
+ * Built on the shared `makeFootnoteDefinition` factory (footnote-authoring.ts);
+ * the only extra is a fresh block id on the inner paragraph (Docmost stamps one,
+ * and the canonicalizer preserves attrs as-is). Single factory, one place to
+ * change the definition shape.
  */
 export function footnoteDefinition(id: string, inlineNodes: any[]): any {
-  const content = Array.isArray(inlineNodes) ? clone(inlineNodes) : [];
-  return {
-    type: "footnoteDefinition",
-    attrs: { id },
-    content: [{ type: "paragraph", attrs: { id: freshId() }, content }],
-  };
+  const node = makeFootnoteDefinition(id, inlineNodes);
+  node.content[0].attrs = { id: freshId() };
+  return node;
 }
 
 /**
@@ -559,3 +657,131 @@ export function commentsToFootnotes(
 
   return { doc: synced.doc, consumed };
 }
+
+/** Options for insertInlineFootnote. */
+export interface InsertInlineFootnoteOptions {
+  /** Body text after which the footnote marker is placed (mark-safe). */
+  anchorText: string;
+  /** Footnote content as markdown (converted to inline nodes). */
+  text: string;
+}
+
+/** Result of insertInlineFootnote. */
+export interface InsertInlineFootnoteResult {
+  doc: any;
+  /** False when the anchor text was not found (no write). */
+  inserted: boolean;
+  /** The footnote id used (new or reused). */
+  footnoteId: string;
+  /** True when an existing same-content definition was reused (content dedup). */
+  reused: boolean;
+}
+
+/**
+ * AUTHOR-INLINE footnote insertion. The caller supplies WHERE (anchorText) and
+ * WHAT (markdown text); numbering and the bottom list are derived server-side by
+ * `canonicalizeFootnotes`. The caller never sees or edits `footnotesList`, never
+ * assigns a number, and cannot desync — orphans / out-of-order lists / raw
+ * `[^id]` markdown are structurally impossible.
+ *
+ * Content DEDUP (#3 in the issue): if an existing definition has the SAME
+ * normalized content key, its id is REUSED (the new reference points at it: one
+ * number, one definition, several references). Otherwise a fresh uuid id is
+ * minted and a new definition added. Conservative — only an exact content match
+ * merges.
+ *
+ * Mechanics: the `footnoteReference` node is inserted DIRECTLY at the anchor via
+ * the same mark-safe split as `insertMarkerAfter` (the shared
+ * `insertNodesAfterAnchor` core), so it hugs the preceding word with no text
+ * sentinel round-trip. The whole document is then canonicalized.
+ *
+ * Operates on a clone of `doc`. When the anchor is not found, returns the input
+ * unchanged with `inserted:false`.
+ */
+export function insertInlineFootnote(
+  doc: any,
+  opts: InsertInlineFootnoteOptions,
+): InsertInlineFootnoteResult {
+  const inline = mdToInlineNodes(opts.text ?? "");
+  // footnoteContentKey only reads `.content`, so key off the inline array
+  // directly instead of building a throwaway definition node.
+  const key = footnoteContentKey({ content: inline });
+
+  // Content dedup: reuse an existing definition's id when its key matches.
+  let footnoteId: string | null = null;
+  let reused = false;
+  if (key !== "") {
+    walk(doc, (n) => {
+      if (
+        footnoteId == null &&
+        isObject(n) &&
+        n.type === "footnoteDefinition" &&
+        n.attrs &&
+        typeof n.attrs.id === "string" &&
+        n.attrs.id !== "" &&
+        footnoteContentKey(n) === key
+      ) {
+        footnoteId = n.attrs.id;
+        reused = true;
+      }
+    });
+  }
+  if (footnoteId == null) footnoteId = generateFootnoteId();
+
+  // Insert the footnoteReference node directly after the anchor (mark-safe
+  // split); it hugs the preceding word with no leading space. Two guards keep the
+  // inline atom out of the notes section and out of blocks that cannot hold it:
+  //  - beforeBlock bounds the search to the BODY, before the first top-level block
+  //    that IS or CONTAINS (at any depth) a footnotesList/footnoteDefinition — so
+  //    a NESTED list or a bare definition also bounds the search, not just a
+  //    top-level list;
+  //  - skipSubtreeTypes refuses to descend into any footnotesList/footnoteDefinition
+  //    subtree, so a reference is never glued inside an existing definition (which
+  //    the canonicalizer would then drop as an orphan, losing that definition's
+  //    prose); and forbidBlockTypes refuses codeBlocks (an inline atom there is a
+  //    schema-invalid doc; insert_footnote skips validateDocStructure).
+  // When the only anchor match is in such a place, the insert is refused and the
+  // write aborts cleanly (inserted:false) instead of destroying content.
+  const boundaryIdx = Array.isArray(doc?.content)
+    ? doc.content.findIndex((n: any) => containsFootnoteNotes(n))
+    : -1;
+  const r = insertNodesAfterAnchor(
+    doc,
+    (opts.anchorText ?? "").trimEnd(),
+    () => [{ type: "footnoteReference", attrs: { id: footnoteId } }],
+    {
+      ...(boundaryIdx >= 0 ? { beforeBlock: boundaryIdx } : {}),
+      forbidBlockTypes: INLINE_ATOM_FORBIDDEN_BLOCKS,
+      skipSubtreeTypes: FOOTNOTE_NOTES_SUBTREES,
+    },
+  );
+  if (!r.inserted) {
+    return { doc: clone(doc), inserted: false, footnoteId, reused };
+  }
+  let working = r.doc;
+
+  // Add a NEW definition (canonicalize will order/place it); a reused id needs
+  // no new definition (the existing one is shared).
+  if (!reused) {
+    appendDefinition(working, makeFootnoteDefinition(footnoteId, inline));
+  }
+
+  // Derive numbering + the single bottom list deterministically.
+  working = canonicalizeFootnotes(working);
+  return { doc: working, inserted: true, footnoteId, reused };
+}
+
+/**
+ * Append a definition node so the canonicalizer can order/place it: into the
+ * first existing footnotesList, or a new trailing list when none exists.
+ */
+function appendDefinition(doc: any, defNode: any): void {
+  const existingList = getList(doc, (n) => isObject(n) && n.type === "footnotesList");
+  if (existingList && Array.isArray(existingList.content)) {
+    existingList.content.push(defNode);
+    return;
+  }
+  if (Array.isArray(doc.content)) {
+    doc.content.push({ type: "footnotesList", content: [defNode] });
+  }
+}
diff --git a/packages/mcp/test/mock/footnote-write.test.mjs b/packages/mcp/test/mock/footnote-write.test.mjs
new file mode 100644
index 00000000..29196b39
--- /dev/null
+++ b/packages/mcp/test/mock/footnote-write.test.mjs
@@ -0,0 +1,153 @@
+// Mock-HTTP orchestration tests for the footnote WRITE wrappers on DocmostClient
+// (issue #228):
+//  - insertFootnote (#11): the required-argument guards reject BEFORE any write,
+//    and never touch the collab/mutate path.
+//  - transformPage / docmost_transform (#13): the auto-canonicalize step
+//    (`result = canonicalizeFootnotes(raw)`) runs after every transform, so a
+//    transform that introduces an orphan footnote definition is silently tidied
+//    away — observable as an EMPTY diff in a dryRun preview.
+//
+// These stand a local http.createServer in for Docmost and only exercise plain
+// HTTP routes (login / comments / pages.info), deliberately avoiding the live
+// Hocuspocus collab WebSocket: the insertFootnote guards short-circuit before it,
+// and docmost_transform's dryRun preview never opens it. The collab mutate path
+// itself — abort-via-throw on a missing anchor with NO persisted write, and the
+// reused-vs-new response shaping — is covered in
+// test/mock/insert-footnote-wrapper.test.mjs (which overrides the mutatePage
+// seam to drive the transform), not here.
+import { test, after } from "node:test";
+import assert from "node:assert/strict";
+import http from "node:http";
+import { DocmostClient } from "../../build/client.js";
+
+function readBody(req) {
+  return new Promise((resolve) => {
+    let raw = "";
+    req.on("data", (c) => (raw += c));
+    req.on("end", () => resolve(raw));
+  });
+}
+function startServer(handler) {
+  return new Promise((resolve) => {
+    const server = http.createServer(handler);
+    server.listen(0, "127.0.0.1", () => {
+      const { port } = server.address();
+      resolve({ server, baseURL: `http://127.0.0.1:${port}/api` });
+    });
+  });
+}
+function sendJson(res, status, obj, extraHeaders = {}) {
+  res.writeHead(status, { "Content-Type": "application/json", ...extraHeaders });
+  res.end(JSON.stringify(obj));
+}
+const openServers = [];
+async function spawn(handler) {
+  const { server, baseURL } = await startServer(handler);
+  openServers.push(server);
+  return { baseURL };
+}
+after(async () => {
+  await Promise.all(openServers.map((s) => new Promise((r) => s.close(r))));
+});
+
+const ref = (id) => ({ type: "footnoteReference", attrs: { id } });
+const def = (id, text) => ({
+  type: "footnoteDefinition",
+  attrs: { id },
+  content: [{ type: "paragraph", content: [{ type: "text", text }] }],
+});
+
+// ---------------------------------------------------------------------------
+// #11 insertFootnote guards: missing anchorText / text reject and never write.
+// ---------------------------------------------------------------------------
+test("insertFootnote rejects a missing anchorText before any write", async () => {
+  const otherRoutes = [];
+  const { baseURL } = await spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      return sendJson(res, 200, { success: true }, {
+        "Set-Cookie": "authToken=t; Path=/; HttpOnly",
+      });
+    }
+    otherRoutes.push(req.url);
+    sendJson(res, 404, { message: "not found" });
+  });
+  const client = new DocmostClient(baseURL, "user@example.com", "pw");
+  await assert.rejects(
+    () => client.insertFootnote("page-1", "   ", "a note"),
+    /anchorText is required/i,
+  );
+  assert.deepEqual(otherRoutes, [], "must not hit any write route");
+});
+
+test("insertFootnote rejects an empty text before any write", async () => {
+  const otherRoutes = [];
+  const { baseURL } = await spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      return sendJson(res, 200, { success: true }, {
+        "Set-Cookie": "authToken=t; Path=/; HttpOnly",
+      });
+    }
+    otherRoutes.push(req.url);
+    sendJson(res, 404, { message: "not found" });
+  });
+  const client = new DocmostClient(baseURL, "user@example.com", "pw");
+  await assert.rejects(
+    () => client.insertFootnote("page-1", "anchor", "   "),
+    /text is required/i,
+  );
+  assert.deepEqual(otherRoutes, [], "must not hit any write route");
+});
+
+// ---------------------------------------------------------------------------
+// #13 docmost_transform auto-canonicalization: a transform that adds an orphan
+// footnote definition produces NO net change (the canonicalizer drops it), so a
+// dryRun preview reports an empty diff. Without the auto-canonicalize step the
+// orphan would survive and the diff would be non-empty.
+// ---------------------------------------------------------------------------
+test("transformPage dryRun auto-canonicalizes footnotes (orphan def is dropped)", async () => {
+  // A page already in canonical footnote state (refs b,a; defs b,a).
+  const pageContent = {
+    type: "doc",
+    content: [
+      { type: "paragraph", content: [{ type: "text", text: "x" }, ref("b"), ref("a")] },
+      { type: "footnotesList", content: [def("b", "B"), def("a", "A")] },
+    ],
+  };
+  const { baseURL } = await spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      return sendJson(res, 200, { success: true }, {
+        "Set-Cookie": "authToken=t; Path=/; HttpOnly",
+      });
+    }
+    if (req.url === "/api/comments") {
+      return sendJson(res, 200, { data: { items: [], meta: { nextCursor: null } } });
+    }
+    if (req.url === "/api/pages/info") {
+      return sendJson(res, 200, {
+        data: { id: "page-1", slugId: "s", title: "P", spaceId: "sp", content: pageContent },
+      });
+    }
+    sendJson(res, 404, { message: "not found" });
+  });
+  const client = new DocmostClient(baseURL, "user@example.com", "pw");
+
+  // The transform appends an ORPHAN definition (id "z", no matching reference).
+  const transformJs = `(doc) => {
+    const list = doc.content.find((n) => n.type === "footnotesList");
+    list.content.push({
+      type: "footnoteDefinition",
+      attrs: { id: "z" },
+      content: [{ type: "paragraph", content: [{ type: "text", text: "orphan" }] }],
+    });
+    return doc;
+  }`;
+
+  const result = await client.transformPage("page-1", transformJs, { dryRun: true });
+  assert.equal(result.pushed, false);
+  // Auto-canonicalize dropped the orphan, so the doc is unchanged => empty diff.
+  assert.equal(result.diff.summary.inserted, 0, "orphan def must be canonicalized away");
+  assert.equal(result.diff.summary.deleted, 0);
+});
diff --git a/packages/mcp/test/mock/full-doc-write-canonicalize.test.mjs b/packages/mcp/test/mock/full-doc-write-canonicalize.test.mjs
new file mode 100644
index 00000000..8fcdf4a2
--- /dev/null
+++ b/packages/mcp/test/mock/full-doc-write-canonicalize.test.mjs
@@ -0,0 +1,78 @@
+// Footnote-canonicalization binding tests for the MCP FULL-document write tools
+// (issue #228, review #4): update_page_json and copy_page_content must persist a
+// footnote-canonical doc. These override the `replacePage` seam (symmetric to the
+// `mutatePage` seam used by the insert-footnote-wrapper test) to capture the
+// persisted doc WITHOUT a live Hocuspocus collab socket. Symmetric to the
+// server-side focus specs for createPage / updatePageContent('replace').
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { DocmostClient } from "../../build/client.js";
+
+const para = (...c) => ({ type: "paragraph", content: c });
+const ref = (id) => ({ type: "footnoteReference", attrs: { id } });
+const def = (id, text) => ({
+  type: "footnoteDefinition",
+  attrs: { id },
+  content: [{ type: "paragraph", content: [{ type: "text", text }] }],
+});
+const list = (...d) => ({ type: "footnotesList", content: d });
+
+function findAll(node, type, acc = []) {
+  if (!node || typeof node !== "object") return acc;
+  if (node.type === type) acc.push(node);
+  if (Array.isArray(node.content)) for (const c of node.content) findAll(c, type, acc);
+  return acc;
+}
+const defIds = (doc) => findAll(doc, "footnoteDefinition").map((d) => d.attrs.id);
+
+function makeClient(sourceDoc) {
+  const calls = { replaced: [] };
+  class TestClient extends DocmostClient {
+    async ensureAuthenticated() {}
+    async getCollabTokenWithReauth() {
+      return "collab-token";
+    }
+    async getPageRaw(pageId) {
+      return { id: pageId, slugId: "s", title: "P", spaceId: "sp", content: sourceDoc };
+    }
+    async replacePage(pageId, doc, token, apiUrl) {
+      calls.replaced.push({ pageId, doc });
+      return { doc, verify: { ok: true } };
+    }
+  }
+  const client = new TestClient("http://127.0.0.1:1/api", "e@x.com", "pw");
+  return { client, calls };
+}
+
+test("update_page_json canonicalizes the persisted full doc (out-of-order -> reference order)", async () => {
+  const { client, calls } = makeClient();
+  const outOfOrder = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "x" }, ref("b"), ref("a")),
+      list(def("a", "A"), def("b", "B")),
+    ],
+  };
+  await client.updatePageJson("p1", outOfOrder);
+  assert.equal(calls.replaced.length, 1);
+  // Definitions reordered to reference order [b, a] before persisting.
+  assert.deepEqual(defIds(calls.replaced[0].doc), ["b", "a"]);
+  assert.equal(findAll(calls.replaced[0].doc, "footnotesList").length, 1);
+});
+
+test("copy_page_content canonicalizes the persisted copy (orphan definition dropped)", async () => {
+  const sourceDoc = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "x" }, ref("a")),
+      list(def("a", "A"), def("orphan", "O")),
+    ],
+  };
+  const { client, calls } = makeClient(sourceDoc);
+  const res = await client.copyPageContent("src", "dst");
+  assert.equal(calls.replaced.length, 1);
+  assert.equal(calls.replaced[0].pageId, "dst");
+  // The orphan definition is dropped by canonicalization before the copy lands.
+  assert.deepEqual(defIds(calls.replaced[0].doc), ["a"]);
+  assert.equal(res.success, true);
+});
diff --git a/packages/mcp/test/mock/insert-footnote-wrapper.test.mjs b/packages/mcp/test/mock/insert-footnote-wrapper.test.mjs
new file mode 100644
index 00000000..887806b7
--- /dev/null
+++ b/packages/mcp/test/mock/insert-footnote-wrapper.test.mjs
@@ -0,0 +1,100 @@
+// Wrapper tests for DocmostClient.insertFootnote (issue #228, review #11/#9):
+// the page-locked write seam (mutatePage) is overridden so the wrapper's
+// transform + response shaping can be exercised WITHOUT a live Hocuspocus collab
+// socket. We assert the two guarantees that the pure insertInlineFootnote test
+// can NOT prove on its own:
+//   - a missing anchor makes the transform throw "anchor text not found" and NO
+//     document is persisted (the no-partial-write guarantee), and
+//   - a success shapes footnoteId / reused / message / verify and writes a doc
+//     carrying the new reference + the derived single list.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { DocmostClient } from "../../build/client.js";
+
+const para = (...c) => ({ type: "paragraph", content: c });
+const ref = (id) => ({ type: "footnoteReference", attrs: { id } });
+const def = (id, text) => ({
+  type: "footnoteDefinition",
+  attrs: { id },
+  content: [{ type: "paragraph", content: [{ type: "text", text }] }],
+});
+const list = (...d) => ({ type: "footnotesList", content: d });
+
+function findAll(node, type, acc = []) {
+  if (!node || typeof node !== "object") return acc;
+  if (node.type === type) acc.push(node);
+  if (Array.isArray(node.content)) for (const c of node.content) findAll(c, type, acc);
+  return acc;
+}
+
+// A DocmostClient whose auth + page-locked write are stubbed; `mutatePage`
+// mirrors collaboration.mutatePageContent (run the transform against a clone of
+// the live doc; if it throws, persist NOTHING and rethrow).
+function makeClient(liveDoc) {
+  const calls = { writes: [] };
+  class TestClient extends DocmostClient {
+    async ensureAuthenticated() {}
+    async getCollabTokenWithReauth() {
+      return "collab-token";
+    }
+    async mutatePage(pageId, token, apiUrl, transform) {
+      calls.pageId = pageId;
+      calls.token = token;
+      const newDoc = transform(structuredClone(liveDoc));
+      calls.writes.push(newDoc);
+      return { doc: newDoc, verify: { ok: true, marker: "v" } };
+    }
+  }
+  const client = new TestClient("http://127.0.0.1:1/api", "e@x.com", "pw");
+  return { client, calls };
+}
+
+test("insertFootnote: anchor not found -> throws and persists nothing", async () => {
+  const { client, calls } = makeClient({
+    type: "doc",
+    content: [para({ type: "text", text: "nothing to anchor on" })],
+  });
+  await assert.rejects(
+    () => client.insertFootnote("p1", "ZZZ", "a note"),
+    /anchor text not found/i,
+  );
+  assert.equal(calls.writes.length, 0, "no document may be persisted on a missing anchor");
+});
+
+test("insertFootnote: success (new) writes a reference + derived list and shapes the response", async () => {
+  const { client, calls } = makeClient({
+    type: "doc",
+    content: [para({ type: "text", text: "The sky is blue today." })],
+  });
+  const res = await client.insertFootnote("p1", "blue", "Rayleigh scattering.");
+  assert.equal(res.success, true);
+  assert.equal(res.modified, true);
+  assert.equal(res.pageId, "p1");
+  assert.equal(res.reused, false);
+  assert.equal(typeof res.footnoteId, "string");
+  assert.ok(res.footnoteId.length > 0);
+  assert.equal(res.message, "Footnote inserted.");
+  assert.deepEqual(res.verify, { ok: true, marker: "v" });
+  assert.equal(calls.writes.length, 1, "exactly one write persisted");
+  assert.equal(findAll(calls.writes[0], "footnoteReference").length, 1);
+  assert.equal(findAll(calls.writes[0], "footnotesList").length, 1);
+  assert.equal(calls.pageId, "p1");
+});
+
+test("insertFootnote: success (reused) reuses the existing definition and reports it", async () => {
+  const liveDoc = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "Alpha and beta." }, ref("a")),
+      list(def("a", "shared note")),
+    ],
+  };
+  const { client, calls } = makeClient(liveDoc);
+  const res = await client.insertFootnote("p1", "beta", "shared note");
+  assert.equal(res.reused, true);
+  assert.equal(res.footnoteId, "a");
+  assert.match(res.message, /reused an existing same-content definition/i);
+  // Still exactly one definition (the reused one), two references to it.
+  assert.equal(findAll(calls.writes[0], "footnoteDefinition").length, 1);
+  assert.equal(findAll(calls.writes[0], "footnoteReference").length, 2);
+});
diff --git a/packages/mcp/test/unit/collaboration.test.mjs b/packages/mcp/test/unit/collaboration.test.mjs
index ab07a414..84801840 100644
--- a/packages/mcp/test/unit/collaboration.test.mjs
+++ b/packages/mcp/test/unit/collaboration.test.mjs
@@ -4,6 +4,7 @@ import assert from "node:assert/strict";
 import {
   buildCollabWsUrl,
   markdownToProseMirror,
+  markdownToProseMirrorCanonical,
 } from "../../build/lib/collaboration.js";
 
 /** Recursively find the first descendant node (or self) of the given type. */
@@ -124,3 +125,38 @@ test("markdownToProseMirror: an aligned GFM table maps header alignment", async
     ["left", "center", "right"],
   );
 });
+
+// Comment-body data-loss guard (#228 review #4): markdownToProseMirror is reused
+// for COMMENT bodies (createComment/updateComment), so it must NOT canonicalize —
+// a comment may legitimately carry a standalone footnote definition with no
+// matching reference, and canonicalization would drop the whole list (the text
+// would vanish). The page-write variant DOES canonicalize.
+test("markdownToProseMirror (comment path) PRESERVES a reference-less footnote definition", async () => {
+  const md = "A comment.\n\n[^1]: a standalone footnote definition";
+  const doc = await markdownToProseMirror(md);
+  const defs = findAll(doc, "footnoteDefinition");
+  assert.equal(defs.length, 1, "the footnote definition must be preserved");
+  assert.match(
+    JSON.stringify(doc),
+    /a standalone footnote definition/,
+    "the definition text must survive the comment write path",
+  );
+});
+
+test("markdownToProseMirrorCanonical (page path) DROPS a reference-less footnote definition", async () => {
+  // Same input through the PAGE variant: with no reference, the canonical doc has
+  // no footnotesList (this is the page-side behavior the comment path must avoid).
+  const md = "A page.\n\n[^1]: a standalone footnote definition";
+  const doc = await markdownToProseMirrorCanonical(md);
+  assert.equal(findAll(doc, "footnotesList").length, 0);
+  assert.equal(findAll(doc, "footnoteDefinition").length, 0);
+});
+
+test("markdownToProseMirrorCanonical still canonicalizes a real page footnote (order)", async () => {
+  // Page path must STILL canonicalize: refs b,a -> definitions reorder to b,a.
+  const md = "See[^b] then[^a].\n\n[^a]: alpha\n[^b]: bravo";
+  const doc = await markdownToProseMirrorCanonical(md);
+  const defs = findAll(doc, "footnoteDefinition").map((d) => d.attrs.id);
+  assert.deepEqual(defs, ["b", "a"]);
+  assert.equal(findAll(doc, "footnotesList").length, 1);
+});
diff --git a/packages/mcp/test/unit/footnote-canonicalize.test.mjs b/packages/mcp/test/unit/footnote-canonicalize.test.mjs
new file mode 100644
index 00000000..e626b316
--- /dev/null
+++ b/packages/mcp/test/unit/footnote-canonicalize.test.mjs
@@ -0,0 +1,286 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { canonicalizeFootnotes } from "../../build/lib/footnote-canonicalize.js";
+import {
+  footnoteContentKey,
+  generateFootnoteId,
+} from "../../build/lib/footnote-authoring.js";
+import { insertInlineFootnote } from "../../build/lib/transforms.js";
+import { markdownToProseMirrorCanonical } from "../../build/lib/collaboration.js";
+
+function findAll(node, type, acc = []) {
+  if (!node || typeof node !== "object") return acc;
+  if (node.type === type) acc.push(node);
+  if (Array.isArray(node.content)) {
+    for (const c of node.content) findAll(c, type, acc);
+  }
+  return acc;
+}
+const defIds = (doc) =>
+  findAll(doc, "footnoteDefinition").map((d) => d.attrs.id);
+const refIds = (doc) =>
+  findAll(doc, "footnoteReference").map((r) => r.attrs.id);
+
+const ref = (id) => ({ type: "footnoteReference", attrs: { id } });
+const def = (id, text) => ({
+  type: "footnoteDefinition",
+  attrs: { id },
+  content: [{ type: "paragraph", content: [{ type: "text", text }] }],
+});
+const para = (...inline) => ({ type: "paragraph", content: inline });
+const list = (...defs) => ({ type: "footnotesList", content: defs });
+
+// The ordering / orphan-drop / no-refs / duplicate-first-wins cases are covered
+// (with full deepEqual on input -> expected) by the shared golden corpus in
+// footnote-corpus.test.mjs; only the input-immutability and idempotence
+// properties — which the corpus does not assert — are kept here.
+
+test("canonicalize is idempotent", () => {
+  const doc = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "x" }, ref("b"), ref("a")),
+      list(def("a", "A"), def("b", "B"), def("orphan", "O")),
+    ],
+  };
+  const once = canonicalizeFootnotes(doc);
+  const twice = canonicalizeFootnotes(once);
+  assert.deepEqual(twice, once);
+});
+
+test("canonicalize does not mutate its input", () => {
+  const doc = {
+    type: "doc",
+    content: [para({ type: "text", text: "x" }, ref("a")), list(def("o", "O"))],
+  };
+  const snap = JSON.parse(JSON.stringify(doc));
+  canonicalizeFootnotes(doc);
+  assert.deepEqual(doc, snap);
+});
+
+test("footnoteContentKey: same text -> same key; formatting differs -> different key", () => {
+  const plain = def("x", "hello world");
+  const sameText = def("y", "hello   world"); // whitespace-collapsed match
+  const bold = {
+    type: "footnoteDefinition",
+    attrs: { id: "z" },
+    content: [
+      {
+        type: "paragraph",
+        content: [
+          { type: "text", text: "hello world", marks: [{ type: "bold" }] },
+        ],
+      },
+    ],
+  };
+  assert.equal(footnoteContentKey(plain), footnoteContentKey(sameText));
+  assert.notEqual(footnoteContentKey(plain), footnoteContentKey(bold));
+});
+
+test("insertInlineFootnote: places a reference at the anchor and derives the list", () => {
+  const doc = {
+    type: "doc",
+    content: [para({ type: "text", text: "The sky is blue today." })],
+  };
+  const r = insertInlineFootnote(doc, {
+    anchorText: "blue",
+    text: "Rayleigh scattering.",
+  });
+  assert.equal(r.inserted, true);
+  assert.equal(r.reused, false);
+  assert.equal(refIds(r.doc).length, 1);
+  assert.deepEqual(defIds(r.doc), [r.footnoteId]);
+  // The marker hugs the anchor word (no leading space text run before the ref).
+  assert.equal(findAll(r.doc, "footnotesList").length, 1);
+});
+
+test("insertInlineFootnote: content dedup -> same text reuses one definition, two refs", () => {
+  let doc = {
+    type: "doc",
+    content: [para({ type: "text", text: "Alpha and beta and gamma." })],
+  };
+  const r1 = insertInlineFootnote(doc, {
+    anchorText: "Alpha",
+    text: "shared note",
+  });
+  const r2 = insertInlineFootnote(r1.doc, {
+    anchorText: "beta",
+    text: "shared note",
+  });
+  assert.equal(r2.reused, true);
+  assert.equal(r2.footnoteId, r1.footnoteId);
+  // One definition, two references both pointing at it.
+  assert.deepEqual(defIds(r2.doc), [r1.footnoteId]);
+  assert.deepEqual(refIds(r2.doc), [r1.footnoteId, r1.footnoteId]);
+});
+
+test("insertInlineFootnote: distinct text -> two definitions numbered by reference order", () => {
+  let doc = {
+    type: "doc",
+    content: [para({ type: "text", text: "First point, second point." })],
+  };
+  const r1 = insertInlineFootnote(doc, { anchorText: "First", text: "note one" });
+  const r2 = insertInlineFootnote(r1.doc, {
+    anchorText: "second",
+    text: "note two",
+  });
+  assert.equal(r2.reused, false);
+  // Reference order in the body is [First-ref, second-ref]; the derived list
+  // matches that order.
+  assert.deepEqual(defIds(r2.doc), refIds(r2.doc));
+  assert.equal(defIds(r2.doc).length, 2);
+});
+
+test("insertInlineFootnote: anchor not found -> inserted:false, no write", () => {
+  const doc = {
+    type: "doc",
+    content: [para({ type: "text", text: "nothing to anchor on" })],
+  };
+  const r = insertInlineFootnote(doc, { anchorText: "ZZZ", text: "x" });
+  assert.equal(r.inserted, false);
+  assert.equal(findAll(r.doc, "footnoteReference").length, 0);
+});
+
+test("insertInlineFootnote: anchor ONLY inside a codeBlock -> refused (no invalid doc)", () => {
+  // A footnoteReference is an inline atom; codeBlock content is text-only, so
+  // splicing one in would persist a schema-invalid doc. The insert must refuse.
+  const doc = {
+    type: "doc",
+    content: [{ type: "codeBlock", content: [{ type: "text", text: "const blue = 1;" }] }],
+  };
+  const r = insertInlineFootnote(doc, { anchorText: "blue", text: "Rayleigh." });
+  assert.equal(r.inserted, false);
+  assert.equal(findAll(r.doc, "footnoteReference").length, 0);
+  assert.equal(findAll(r.doc, "footnotesList").length, 0);
+  // The codeBlock text is untouched.
+  assert.deepEqual(r.doc, doc);
+});
+
+test("insertInlineFootnote: anchor ONLY inside an existing footnote definition -> refused", () => {
+  // The anchor text lives in a definition (inside the footnotesList). The search
+  // is bounded to the BODY (before the first list), so it is not matched there
+  // and the insert is refused rather than nesting a reference in a definition.
+  const doc = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "Hello world." }, ref("a")),
+      list(def("a", "the sky is blue")),
+    ],
+  };
+  const r = insertInlineFootnote(doc, { anchorText: "sky", text: "note" });
+  assert.equal(r.inserted, false);
+  // No EXTRA reference and still exactly one (the pre-existing) list/definition.
+  assert.equal(findAll(r.doc, "footnoteReference").length, 1);
+  assert.deepEqual(defIds(r.doc), ["a"]);
+});
+
+test("insertInlineFootnote: codeBlock match is skipped, a later body paragraph still anchors", () => {
+  // The anchor first appears in a codeBlock (refused) but also in a normal
+  // paragraph after it; the insert falls through to the valid block.
+  const doc = {
+    type: "doc",
+    content: [
+      { type: "codeBlock", content: [{ type: "text", text: "let token = 1;" }] },
+      para({ type: "text", text: "The token is rotated daily." }),
+    ],
+  };
+  const r = insertInlineFootnote(doc, { anchorText: "token", text: "secret" });
+  assert.equal(r.inserted, true);
+  // The reference landed in the paragraph, NOT the codeBlock.
+  const code = findAll(r.doc, "codeBlock")[0];
+  assert.equal(findAll(code, "footnoteReference").length, 0);
+  assert.equal(findAll(r.doc, "footnoteReference").length, 1);
+});
+
+test("insertInlineFootnote: anchor only inside a NESTED definition -> refused, definition preserved", () => {
+  // The footnotesList is nested in a callout (not top level) and the anchor text
+  // appears ONLY inside that definition. The search must be bounded past the
+  // notes subtree (recursive boundary) AND refuse to descend into the definition,
+  // so it aborts cleanly instead of gluing a reference into the definition (which
+  // canonicalize would then drop as an orphan, losing the definition's prose).
+  const doc = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "Body text here." }, ref("a")),
+      {
+        type: "callout",
+        content: [list(def("a", "the unique anchor lives here"))],
+      },
+    ],
+  };
+  const r = insertInlineFootnote(doc, {
+    anchorText: "unique anchor",
+    text: "new note",
+  });
+  assert.equal(r.inserted, false);
+  // The existing definition (and its text) is preserved untouched.
+  assert.equal(findAll(r.doc, "footnoteDefinition").length, 1);
+  assert.match(JSON.stringify(r.doc), /the unique anchor lives here/);
+  assert.equal(findAll(r.doc, "footnoteReference").length, 1); // only the original
+});
+
+test("insertInlineFootnote: anchor only inside a BARE definition (no list wrapper) -> refused", () => {
+  const doc = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "Some body." }),
+      {
+        type: "footnoteDefinition",
+        attrs: { id: "a" },
+        content: [{ type: "paragraph", content: [{ type: "text", text: "orphan anchor text" }] }],
+      },
+    ],
+  };
+  const r = insertInlineFootnote(doc, { anchorText: "orphan anchor", text: "x" });
+  assert.equal(r.inserted, false);
+  assert.equal(findAll(r.doc, "footnoteDefinition").length, 1);
+  assert.match(JSON.stringify(r.doc), /orphan anchor text/);
+});
+
+test("insertInlineFootnote: anchor in body BEFORE a nested list still inserts", () => {
+  const doc = {
+    type: "doc",
+    content: [
+      para({ type: "text", text: "The sky is blue." }, ref("a")),
+      { type: "callout", content: [list(def("a", "note a"))] },
+    ],
+  };
+  const r = insertInlineFootnote(doc, { anchorText: "blue", text: "Rayleigh." });
+  assert.equal(r.inserted, true);
+  // The new reference plus the original = two references; a single canonical list.
+  assert.equal(findAll(r.doc, "footnoteReference").length, 2);
+  assert.equal(findAll(r.doc, "footnotesList").length, 1);
+});
+
+test("markdown import (page path): out-of-order definitions render as a reference-ordered list", async () => {
+  // References appear b, a, c in the body; definitions are written in a, b, c
+  // order (the import order). The PAGE import path (markdownToProseMirrorCanonical)
+  // canonicalizes so the bottom list follows REFERENCE order — numbers read 1, 2,
+  // 3 down the list. (The non-canonicalizing markdownToProseMirror, used for
+  // comment bodies, would keep the import order; see collaboration.test.mjs.)
+  const md = [
+    "See[^b] then[^a] then[^c].",
+    "",
+    "[^a]: alpha",
+    "[^b]: bravo",
+    "[^c]: charlie",
+  ].join("\n");
+  const json = await markdownToProseMirrorCanonical(md);
+  assert.deepEqual(defIds(json), ["b", "a", "c"]);
+  assert.equal(findAll(json, "footnotesList").length, 1);
+});
+
+test("generateFootnoteId: valid uuidv7 shape (version 7, variant 8..b) and unique", () => {
+  // version nibble = 7; variant nibble in [8,9,a,b]; otherwise lowercase hex.
+  const re =
+    /^[0-9a-f]{8}-[0-9a-f]{4}-7[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
+  const ids = new Set();
+  for (let i = 0; i < 50; i++) {
+    const id = generateFootnoteId();
+    assert.match(id, re, `not a uuidv7: ${id}`);
+    ids.add(id);
+  }
+  // Distinct across calls (random component makes collisions astronomically rare).
+  assert.equal(ids.size, 50, "generated ids must be unique");
+});
diff --git a/packages/mcp/test/unit/footnote-corpus-parity.test.mjs b/packages/mcp/test/unit/footnote-corpus-parity.test.mjs
new file mode 100644
index 00000000..5a944395
--- /dev/null
+++ b/packages/mcp/test/unit/footnote-corpus-parity.test.mjs
@@ -0,0 +1,49 @@
+// CI guard for architecture item B: the shared golden corpus is duplicated (the
+// canonical TS copy in editor-ext + the MCP .mjs mirror), so a typo in one copy
+// would otherwise pass BOTH per-package suites green while silently breaking the
+// cross-copy invariant. This test loads BOTH copies and asserts they are
+// deep-equal, turning "the two corpora stay identical" into a checked property.
+//
+// The editor-ext copy is a .ts module (not importable from node:test), so it is
+// read as text and its array literal — which is pure JSON produced by
+// JSON.stringify — is parsed out directly.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { dirname, resolve } from "node:path";
+
+import { FOOTNOTE_CORPUS as MCP_CORPUS } from "./footnote-corpus.mjs";
+
+function loadEditorExtCorpus() {
+  const here = dirname(fileURLToPath(import.meta.url));
+  const tsPath = resolve(
+    here,
+    "../../../editor-ext/src/lib/footnote/footnote-corpus.ts",
+  );
+  const src = readFileSync(tsPath, "utf8");
+  // The value is `export const FOOTNOTE_CORPUS: FootnoteCorpusCase[] = [ ... ];`
+  // where `[ ... ]` is strict JSON (JSON.stringify output). Slice from the
+  // assignment's opening bracket to the final closing bracket and parse.
+  const assignAt = src.indexOf("] = ");
+  assert.ok(assignAt >= 0, "could not locate the editor-ext corpus assignment");
+  const jsonStart = src.indexOf("[", assignAt + 3);
+  const jsonEnd = src.lastIndexOf("]");
+  assert.ok(jsonStart >= 0 && jsonEnd > jsonStart, "could not bound the corpus array");
+  return JSON.parse(src.slice(jsonStart, jsonEnd + 1));
+}
+
+test("the editor-ext and MCP golden corpora are byte-for-byte identical", () => {
+  const editorExt = loadEditorExtCorpus();
+  assert.ok(Array.isArray(editorExt) && editorExt.length > 0, "editor-ext corpus is non-empty");
+  assert.equal(
+    MCP_CORPUS.length,
+    editorExt.length,
+    "the two corpora must have the same number of cases",
+  );
+  assert.deepEqual(
+    MCP_CORPUS,
+    editorExt,
+    "the MCP corpus mirror has drifted from the editor-ext canonical copy — re-sync them",
+  );
+});
diff --git a/packages/mcp/test/unit/footnote-corpus.mjs b/packages/mcp/test/unit/footnote-corpus.mjs
new file mode 100644
index 00000000..648281f4
--- /dev/null
+++ b/packages/mcp/test/unit/footnote-corpus.mjs
@@ -0,0 +1,1255 @@
+// MIRROR (data only) of
+// packages/editor-ext/src/lib/footnote/footnote-corpus.ts — keep the two in
+// sync. Shared golden corpus for the footnote canonicalizer (issue #228): each
+// case is { name, input, expected } where `expected` is exactly what
+// `canonicalizeFootnotes(input)` must return. Running BOTH the editor-ext copy
+// and this MCP mirror against the same corpus makes "the two pure copies behave
+// identically" a checkable property without coupling the packages.
+export const FOOTNOTE_CORPUS = [
+  {
+    "name": "out-of-order defs ordered by first reference",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "b"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "c"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "c"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "C"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "b"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "B"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "D"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "b"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "c"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "b"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "B"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "D"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "c"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "C"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "orphan definition dropped",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "orphan"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "O"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "no references removes the list",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "plain"
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "orphan"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "O"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "plain"
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "reuse: repeated references collapse to one definition",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "text",
+              "text": " a "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "shared"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "text",
+              "text": " a "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "shared"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "duplicate definitions: first wins",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "first"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "second"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "third"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "d"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "d"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "first"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "synthesizes an empty definition for a reference with none",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "missing"
+              }
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "missing"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "missing"
+              },
+              "content": [
+                {
+                  "type": "paragraph"
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "merges multiple footnotesList nodes into one",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "a"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "x"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "y"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "x"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "X"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "tail"
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "y"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "Y"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "a"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "x"
+              }
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "y"
+              }
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "tail"
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "x"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "X"
+                    }
+                  ]
+                }
+              ]
+            },
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "y"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "Y"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "single canonical list before a trailing empty paragraph stays put",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph"
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph"
+        }
+      ]
+    }
+  },
+  {
+    "name": "single canonical list with NON-EMPTY content after it is NOT moved (plugin parity)",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "epilogue text"
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "x"
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "epilogue text"
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "reference inside a nested container (callout) is collected",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "callout",
+          "content": [
+            {
+              "type": "paragraph",
+              "content": [
+                {
+                  "type": "text",
+                  "text": "see "
+                },
+                {
+                  "type": "footnoteReference",
+                  "attrs": {
+                    "id": "n"
+                  }
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "n"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "callout",
+          "content": [
+            {
+              "type": "paragraph",
+              "content": [
+                {
+                  "type": "text",
+                  "text": "see "
+                },
+                {
+                  "type": "footnoteReference",
+                  "attrs": {
+                    "id": "n"
+                  }
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "n"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "bare footnoteDefinition nested in a callout is collected, NOT duplicated",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "see "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "callout",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "see "
+            },
+            {
+              "type": "footnoteReference",
+              "attrs": {
+                "id": "a"
+              }
+            }
+          ]
+        },
+        {
+          "type": "callout",
+          "content": []
+        },
+        {
+          "type": "footnotesList",
+          "content": [
+            {
+              "type": "footnoteDefinition",
+              "attrs": {
+                "id": "a"
+              },
+              "content": [
+                {
+                  "type": "paragraph",
+                  "content": [
+                    {
+                      "type": "text",
+                      "text": "note A"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  {
+    "name": "no footnotes at all is unchanged",
+    "input": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "just text"
+            }
+          ]
+        }
+      ]
+    },
+    "expected": {
+      "type": "doc",
+      "content": [
+        {
+          "type": "paragraph",
+          "content": [
+            {
+              "type": "text",
+              "text": "just text"
+            }
+          ]
+        }
+      ]
+    }
+  }
+];
diff --git a/packages/mcp/test/unit/footnote-corpus.test.mjs b/packages/mcp/test/unit/footnote-corpus.test.mjs
new file mode 100644
index 00000000..c58fa02a
--- /dev/null
+++ b/packages/mcp/test/unit/footnote-corpus.test.mjs
@@ -0,0 +1,19 @@
+// Runs the MCP mirror of `canonicalizeFootnotes` against the SHARED golden
+// corpus (the same { input -> expected } cases the editor-ext copy is tested
+// against in footnote-canonicalize.test.ts). Pinning identical expected outputs
+// in both suites makes "the editor-ext copy and the MCP mirror behave
+// identically" a checkable property without coupling the two packages
+// (architecture item A). The corpus data is mirrored in footnote-corpus.mjs.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { canonicalizeFootnotes } from "../../build/lib/footnote-canonicalize.js";
+import { FOOTNOTE_CORPUS } from "./footnote-corpus.mjs";
+
+for (const { name, input, expected } of FOOTNOTE_CORPUS) {
+  test(`shared corpus (MCP mirror): ${name}`, () => {
+    assert.deepEqual(canonicalizeFootnotes(input), expected);
+    // Idempotent on the corpus too.
+    assert.deepEqual(canonicalizeFootnotes(expected), expected);
+  });
+}