fix(mcp): pre-flight size-guard в diffDocs против CPU-DoS на больших правках (#464)

Боевой инцидент: diffDocs синхронно зовёт recreateTransform (rfc6902), чей
array-diff — O(n·m) по числу нод и O(w²) по длине прогонов слов, и который
НИКОГДА не бросает. Поэтому существующий catch→coarseDiff не спасает event loop:
большая агентская правка блокирует воркер на секунды→минуты (бенч: 401 нода→1.3с,
801→5.5с, 1601→OOM; отдельная ось — байт-тяжёлый вход: 309КБ→OOM), а это душит
все остальные запросы воркера. Отсюда живой прод-хэнг.

Фикс — pre-flight size-guard ПЕРЕД дорогим вызовом:
- readPositiveIntEnv(name, dflt): парс env каждый вызов; мусор/пусто/≤0/не-finite →
  дефолт, так что guard нельзя случайно отключить.
- exceedsDiffSizeGuard(old, new): срабатывает по max(old,new) на ОБЕИХ осях —
  countNodes и JSON.stringify().length — так что асимметричная пара (крошечный
  new / огромный old и наоборот) тоже триггерит. Дёшево: один обход + один
  stringify на документ.
- Дефолты MCP_DIFF_MAX_NODES=150, MCP_DIFF_MAX_BYTES=12288 (12 КиБ),
  env-переопределяемы. Подобраны бенчмарком под бюджет ~200мс на ЛЮБОЙ форме
  входа на границе cap'а (исходные догадки тикета 3000-5000 нод / 512КБ-1МБ были
  в 20-30× завышены — пропускали бы многоминутные блоки).
- Рефактор: выделены coarseDiffTally (единый источник формы fellBack:true) и
  preciseDiffTally. Новый поток diffDocs: computeIntegrity (без изменений, для
  обоих путей) → если exceedsDiffSizeGuard → coarseDiffTally(fellBack=true) →
  иначе try preciseDiffTally / catch → coarseDiffTally. Обе деградации дают
  идентичную форму результата.

Fail-closed: единственный путь к recreateTransform — ветка else, достижимая
только когда guard НЕ сработал; огромный документ физически до transform не
доходит. computeIntegrity (корректностный сигнал) считается ВСЕГДА. Все три
call-site потребляют DiffResult как информационный preview, не гейтят запись —
coarse-фоллбэк контракт-сохраняющий.

Тесты (11): over/under-порог, обе асимметрии, байт-ось (нод-мало/байт-много),
env-override низким cap'ом, garbage-env→дефолт (guard не отключается), integrity
корректен на tripped-документе; behavioral-proxy что transform пропущен над
cap'ом (guarded ~5мс vs caps-raised ~3.3с, ≥5× + <200мс бюджет). node --test
688/688. tsc --noEmit чисто. Только packages/mcp, внешний симлинк не тронут.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/develop.yml

@@ -157,6 +157,12 @@ jobs:
       - name: Build prosemirror-markdown
         run: pnpm --filter @docmost/prosemirror-markdown build
 
+      # docmost-client.loader.ts type-imports from @docmost/mcp (issue #446); its
+      # build/ is gitignored and `test:e2e` type-checks, so build it here or tsc
+      # fails with TS2307 (mirrors the e2e-mcp / mcp-server-parity jobs).
+      - name: Build mcp
+        run: pnpm --filter @docmost/mcp build
+
       - name: Run migrations
         run: pnpm --filter ./apps/server migration:latest
 

CHANGELOG.md

@@ -10,6 +10,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Breaking Changes
+
+- **External MCP: `import_page_markdown` removed, `update_page_markdown` added.**
+  The external `/mcp` surface no longer exposes `import_page_markdown` (the
+  round-trip parser for a self-contained *exported* Docmost-Markdown file). In
+  its place it now exposes **`update_page_markdown`** — a plain-Markdown
+  full-body replace (`{pageId, content, title?}`) that pairs with
+  `update_page_json`, re-imports the whole body (block ids regenerate) and
+  parses Docmost-flavoured markdown including `^[...]` inline footnotes.
+  *Migration:* MCP clients that called `import_page_markdown` to overwrite a
+  page's body from Markdown should call `update_page_markdown` instead (pass the
+  markdown as `content`). Round-tripping an exported Docmost-Markdown file with
+  comment anchors/diagrams is no longer available on the external MCP surface;
+  export remains via `export_page_markdown`. The in-app AI agent is unaffected —
+  it keeps both `importPageMarkdown` and the renamed `updatePageMarkdown` (was
+  `updatePageContent`). The total MCP tool count is unchanged (−1 / +1). (#411)
+
 ### Added
 
 - **Place several images side by side in a row.** A new "Inline (side by

apps/server/src/core/ai-chat/chat-markdown.util.ts

@@ -75,7 +75,7 @@ const LABELS: Record<
       searchPages: 'Searched pages',
       getPage: 'Read page',
       createPage: 'Created page',
-      updatePageContent: 'Updated page',
+      updatePageMarkdown: 'Updated page',
       renamePage: 'Renamed page',
       movePage: 'Moved page',
       deletePage: 'Deleted page (to trash)',
@@ -96,7 +96,7 @@ const LABELS: Record<
       searchPages: 'Искал по страницам',
       getPage: 'Прочитал страницу',
       createPage: 'Создал страницу',
-      updatePageContent: 'Обновил страницу',
+      updatePageMarkdown: 'Обновил страницу',
       renamePage: 'Переименовал страницу',
       movePage: 'Переместил страницу',
       deletePage: 'Удалил страницу (в корзину)',

apps/server/src/core/ai-chat/tools/ai-chat-tools.service.spec.ts

@@ -23,7 +23,7 @@ import { SHARED_TOOL_SPECS } from '../../../../../../packages/mcp/src/tool-specs
 // sync.
 const mockLoaded = (DocmostClient: loader.DocmostClientCtor) => ({
   DocmostClient,
-  sharedToolSpecs: SHARED_TOOL_SPECS as Record<string, loader.SharedToolSpec>,
+  sharedToolSpecs: SHARED_TOOL_SPECS as unknown as Record<string, loader.SharedToolSpec>,
   // Pure no-network draw.io helpers (#424). Type-correct stubs: these tests
   // never execute the drawio_shapes / drawio_guide tool bodies.
   searchShapes: (() => []) as unknown as loader.SearchShapesFn,
@@ -283,6 +283,7 @@ describe('AiChatToolsService node-arg JSON-string coercion', () => {
   const patchNodeCalls: unknown[][] = [];
   const insertNodeCalls: unknown[][] = [];
   const updatePageJsonCalls: unknown[][] = [];
+  const updatePageCalls: unknown[][] = [];
 
   const fakeClient: FakeDocmostClient = {
     patchNode: (...args: unknown[]) => {
@@ -297,6 +298,11 @@ describe('AiChatToolsService node-arg JSON-string coercion', () => {
       updatePageJsonCalls.push(args);
       return Promise.resolve({ ok: true });
     },
+    // Backs the plain-Markdown full-body-replace tool updatePageMarkdown (#411).
+    updatePage: (...args: unknown[]) => {
+      updatePageCalls.push(args);
+      return Promise.resolve({ success: true });
+    },
   };
 
   const tokenServiceStub = {
@@ -310,6 +316,7 @@ describe('AiChatToolsService node-arg JSON-string coercion', () => {
     patchNodeCalls.length = 0;
     insertNodeCalls.length = 0;
     updatePageJsonCalls.length = 0;
+    updatePageCalls.length = 0;
     jest.spyOn(loader, 'loadDocmostMcp').mockResolvedValue(
       mockLoaded(function () {
         return fakeClient as DocmostClientLike;
@@ -445,6 +452,54 @@ describe('AiChatToolsService node-arg JSON-string coercion', () => {
     ).rejects.toThrow('content was a string but not valid JSON');
     expect(updatePageJsonCalls).toHaveLength(0);
   });
+
+  // #411: the plain-Markdown full-body-replace tool is now the shared
+  // `updatePageMarkdown` (was inline `updatePageContent`). It forwards to
+  // client.updatePage(pageId, content, title) -> updatePageContentRealtime ->
+  // markdownToProseMirrorCanonical, so `^[...]` footnotes materialize.
+  it('updatePageMarkdown forwards { pageId, content, title } to client.updatePage', async () => {
+    const tools = await buildTools();
+    await tools.updatePageMarkdown.execute(
+      { pageId: 'p1', content: 'Body^[a note]', title: 'New title' } as never,
+      {} as never,
+    );
+    expect(updatePageCalls).toHaveLength(1);
+    expect(updatePageCalls[0]).toEqual(['p1', 'Body^[a note]', 'New title']);
+  });
+
+  it('updatePageMarkdown returns the RAW client result in-app (deliberate #411 shape change, documented on the spec)', async () => {
+    const tools = await buildTools();
+    // Registry canonical execute returns client.updatePage's result verbatim.
+    // The old inline tool projected to { pageId, updated }; the rename now
+    // surfaces the raw result (nothing reads the removed `.updated`; the raw
+    // shape carries footnote/verify warnings and matches the on-both-hosts
+    // registry convention). fakeClient.updatePage resolves { success: true }.
+    const result = await tools.updatePageMarkdown.execute(
+      { pageId: 'p1', content: '# Hi' } as never,
+      {} as never,
+    );
+    expect(result).toEqual({ success: true });
+  });
+
+  it('updatePageMarkdown forwards title=undefined when omitted', async () => {
+    const tools = await buildTools();
+    await tools.updatePageMarkdown.execute(
+      { pageId: 'p1', content: '# Hi' } as never,
+      {} as never,
+    );
+    expect(updatePageCalls[0]).toEqual(['p1', '# Hi', undefined]);
+  });
+
+  // #411 surface split: the plain-Markdown replace tool exists in-app under the
+  // new key; the OLD inline updatePageContent key is gone; importPageMarkdown is
+  // still present IN-APP (only the external MCP surface drops it — asserted in
+  // packages/mcp/test/unit/tool-inventory.test.mjs).
+  it('exposes updatePageMarkdown in-app, no legacy updatePageContent, keeps importPageMarkdown', async () => {
+    const tools = await buildTools();
+    expect(tools.updatePageMarkdown).toBeDefined();
+    expect((tools as Record<string, unknown>).updatePageContent).toBeUndefined();
+    expect(tools.importPageMarkdown).toBeDefined();
+  });
 });
 
 /**

apps/server/src/core/ai-chat/tools/ai-chat-tools.service.ts

@@ -307,8 +307,8 @@ export class AiChatToolsService {
 
     // The in-app toolset. It starts with the tools kept INLINE here for a
     // documented per-layer reason: an intentional behaviour/schema divergence from
-    // the standalone MCP surface (searchPages' hybrid RRF, updatePageContent's
-    // Markdown write, transformPage's guardrailed shorter schema), a
+    // the standalone MCP surface (searchPages' hybrid RRF,
+    // transformPage's guardrailed shorter schema), a
     // snake_case/camelCase naming clash the shared registry forbids (getTable vs
     // the MCP `table_get`), per-request state the registry loop cannot provide
     // (getCurrentPage reads the resolved openedPage; searchPages closes over the
@@ -451,28 +451,13 @@ export class AiChatToolsService {
       }),
 
       // --- WRITE tools (all reversible — history/trash; §6.5 / D3) ---
-
-      updatePageContent: tool({
-        description:
-          "Replace a page's body with new Markdown content (and optionally its " +
-          'title). Reversible: the previous version is kept in page history.',
-        inputSchema: modelFriendlyInput({
-          pageId: z.string().describe('The id of the page to update.'),
-          content: z.string().describe('The new page body as Markdown.'),
-          title: z
-            .string()
-            .optional()
-            .describe('Optional new title for the page.'),
-        }),
-        execute: async ({ pageId, content, title }) => {
-          // updatePage mutates the live collab doc -> provenance flows from the
-          // collab-token provider. Returns { success, modified, message, pageId }.
-          const result = (await client.updatePage(pageId, content, title)) as {
-            success?: boolean;
-          };
-          return { pageId, updated: result?.success ?? true };
-        },
-      }),
+      //
+      // NOTE (issue #411): the plain-Markdown full-body-replace tool is no longer
+      // inline here — it moved to @docmost/mcp's SHARED_TOOL_SPECS as
+      // `updatePageMarkdown` (was inline `updatePageContent`) so it registers on
+      // BOTH the external MCP and the in-app agent. The registry loop below adds
+      // it under its inAppKey. importPageMarkdown stays a shared spec too (now
+      // inAppOnly — dropped from the external MCP surface, kept in-app).
 
       listSidebarPages: tool({
         description:

apps/server/src/core/ai-chat/tools/comment-signal-inapp.spec.ts

@@ -283,7 +283,7 @@ describe('AiChatToolsService forUser + comment signal (real tracker)', () => {
       DocmostClient: function () {
         return fakeClient as DocmostClientLike;
       } as unknown as loader.DocmostClientCtor,
-      sharedToolSpecs: SHARED_TOOL_SPECS as Record<string, loader.SharedToolSpec>,
+      sharedToolSpecs: SHARED_TOOL_SPECS as unknown as Record<string, loader.SharedToolSpec>,
       // Wire the REAL factory so the in-app path is exercised end to end.
       createCommentSignalTracker:
         createCommentSignalTracker as unknown as loader.CommentSignalTrackerFactory,

apps/server/src/core/ai-chat/tools/shared-tool-specs.contract.spec.ts

@@ -80,7 +80,7 @@ describe('SHARED_TOOL_SPECS contract parity', () => {
 
   // Type as the (optional-buildShape) SharedToolSpec; the `satisfies` literal
   // above otherwise narrows to a union where some members lack buildShape.
-  const specEntries = Object.entries(SHARED_TOOL_SPECS) as Array<
+  const specEntries = Object.entries(SHARED_TOOL_SPECS) as unknown as Array<
     [string, loader.SharedToolSpec]
   >;
 

apps/server/src/core/ai-chat/tools/tool-tiers.spec.ts

@@ -123,7 +123,7 @@ describe('deferred catalog ↔ live forUser() toolset partition (#332, F3)', ()
       DocmostClient: function () {
         return {} as DocmostClientLike;
       } as unknown as loader.DocmostClientCtor,
-      sharedToolSpecs: SHARED_TOOL_SPECS as Record<string, loader.SharedToolSpec>,
+      sharedToolSpecs: SHARED_TOOL_SPECS as unknown as Record<string, loader.SharedToolSpec>,
       // Pure no-network draw.io helpers (#424); tool bodies are never executed here.
       searchShapes: (() => []) as unknown as loader.SearchShapesFn,
       getGuideSection: (() => ({

apps/server/src/core/ai-chat/tools/tool-tiers.ts

@@ -124,12 +124,9 @@ export const INLINE_TOOL_TIERS: Record<
   // --- deferred inline ---
   // NOTE: createPage, renamePage, movePage, deletePage, updatePageJson and
   // exportPageMarkdown moved to @docmost/mcp's SHARED_TOOL_SPECS (#294); they
-  // carry their own deferred tier + catalogLine there.
-  updatePageContent: {
-    tier: 'deferred',
-    catalogLine:
-      "updatePageContent — replace a page's body (and optionally title) with new Markdown.",
-  },
+  // carry their own deferred tier + catalogLine there. updatePageContent moved
+  // there too as updatePageMarkdown (#411) — a shared registry spec now, so it
+  // is no longer an inline tier entry.
   listSidebarPages: {
     tier: 'deferred',
     catalogLine:

apps/server/test/integration/ai-chat-attach.int-spec.ts

@@ -182,6 +182,7 @@ describe('AiChatService run-stream attach [integration]', () => {
       {
         isAiChatDeferredToolsEnabled: () => false,
         isAiChatResumableStreamEnabled: () => true,
+        isAiChatFinalStepLockdownEnabled: () => false,
       } as any,
       registry,
     );
@@ -499,6 +500,7 @@ describe('AiChatService run-stream attach [integration]', () => {
       {
         isAiChatDeferredToolsEnabled: () => false,
         isAiChatResumableStreamEnabled: () => true,
+        isAiChatFinalStepLockdownEnabled: () => false,
       } as any,
       registry,
     );

apps/server/test/integration/ai-chat-stream.int-spec.ts

@@ -150,7 +150,7 @@ describe('AiChatService.stream [integration]', () => {
       {} as any, // pageAccess (idem)
       // environment (#332): keep deferred tool loading OFF for this lifecycle
       // harness so the toolset/behavior is exactly as before.
-      { isAiChatDeferredToolsEnabled: () => false } as any,
+      { isAiChatDeferredToolsEnabled: () => false, isAiChatFinalStepLockdownEnabled: () => false } as any,
     );
   }
 
@@ -378,7 +378,7 @@ describe('AiChatService.stream [integration]', () => {
         {} as any,
         {} as any,
         // #332: deferred tool loading ON — the property under test.
-        { isAiChatDeferredToolsEnabled: () => true } as any,
+        { isAiChatDeferredToolsEnabled: () => true, isAiChatFinalStepLockdownEnabled: () => false } as any,
       );
     }
 

packages/mcp/README.md

@@ -155,6 +155,10 @@ All 41 tools, grouped by what you'd reach for them.
 - **`update_page_json`** — Replace a page's entire content with a ProseMirror document
   (bulk rewrites, or when nodes lack ids). `content` is optional — omit it to update only
   the title. Keeps the block ids you pass in, so heading anchors and history stay stable.
+- **`update_page_markdown`** — Replace a page's body (and optionally its title) with new
+  **plain Markdown**. The whole body is re-imported (block ids regenerate — for surgical or
+  id-preserving edits prefer `edit_page_text` / `patch_node` / `update_page_json`).
+  Docmost-flavoured markdown is parsed, including `^[...]` inline footnotes.
 - **`docmost_transform`** — The agent-native editing interface: instead of retyping a
   document, the agent **writes a function that fixes it**. Edit a page by running an
   arbitrary **`(doc, ctx) => doc` JavaScript transform** against its *live* ProseMirror
@@ -184,13 +188,13 @@ All 41 tools, grouped by what you'd reach for them.
 
 - **`export_page_markdown`** — Export a page to a single self-contained, **lossless
   Docmost-flavoured Markdown** file: a meta header, the body with inline comment anchors
-  and diagrams, and a trailing comments-thread block. Built for a download → edit body →
-  `import_page_markdown` round-trip that preserves everything, including comment highlights.
-- **`import_page_markdown`** — Replace a page's content from a Docmost-flavoured Markdown
-  file produced by `export_page_markdown`, restoring comment-highlight anchors and diagrams
-  from their inline HTML. (Comment *threads* in the file are not re-created on the server —
-  only the page body and inline comment marks are written; manage threads via the comment
-  tools/UI.)
+  and diagrams, and a trailing comments-thread block. To replace a page's body from plain
+  authoring Markdown, use `update_page_markdown`.
+
+> **Removed in this release:** `import_page_markdown` (the round-trip parser for an
+> exported Docmost-Markdown file) is **no longer exposed on the external MCP surface**.
+> To replace a page's body from Markdown, use **`update_page_markdown`** (plain Markdown
+> body replace). See the CHANGELOG for the migration note.
 
 ### Images
 
@@ -256,7 +260,8 @@ so capable clients steer the model automatically.
   `delete_node`, addressing the node by its `attrs.id` from `get_page_json`.
 - **Images**: `insert_image` / `replace_image`.
 - **A new page**: `create_page`.
-- **Bulk rewrite, or nodes without ids**: `update_page_json`.
+- **Bulk rewrite, or nodes without ids**: `update_page_json` (ProseMirror) or
+  `update_page_markdown` (plain Markdown body replace).
 - **Multi-step / scripted rewrite** (renumbering, footnotes, coordinated edits):
   `docmost_transform` — preview with `dryRun`, then apply.
 - **Copy a whole page's content from another page** (server-side): `copy_page_content`.
@@ -269,8 +274,8 @@ so capable clients steer the model automatically.
   `get_node`.
 - **Tables** (add/remove a row, set a cell): `table_get` / `table_insert_row` /
   `table_delete_row` / `table_update_cell`.
-- **Round-trip a page as Markdown** (download, edit, re-upload losslessly with comments):
-  `export_page_markdown` / `import_page_markdown`.
+- **Export a page as self-contained Markdown** (with comment anchors): `export_page_markdown`.
+- **Replace a page's body from Markdown**: `update_page_markdown`.
 
 ---
 

packages/mcp/README.ru.md

@@ -161,6 +161,10 @@ Docmost-MCP не сочетают:
   перезаписи или когда у узлов нет id). `content` опционален — опустите его, чтобы изменить
   только заголовок. Сохраняет переданные id блоков, поэтому якоря заголовков и история
   остаются стабильными.
+- **`update_page_markdown`** — Заменить тело страницы (и опционально заголовок) новым
+  **обычным Markdown**. Всё тело переимпортируется (id блоков перегенерируются — для
+  хирургических правок или сохранения id используйте `edit_page_text` / `patch_node` /
+  `update_page_json`). Markdown в диалекте Docmost разбирается, включая inline-сноски `^[...]`.
 - **`docmost_transform`** — Агентоориентированный интерфейс редактирования: вместо
   перепечатывания документа агент **пишет функцию, которая его чинит**. Редактирует
   страницу, запуская произвольный **JS-трансформ `(doc, ctx) => doc`** на её *живом*
@@ -189,14 +193,13 @@ Docmost-MCP не сочетают:
 
 - **`export_page_markdown`** — Экспортировать страницу в один самодостаточный, **lossless
   Markdown в диалекте Docmost**: мета-заголовок, тело с inline-якорями комментариев и
-  диаграммами и завершающий блок тредов комментариев. Рассчитан на цикл «скачать →
-  отредактировать тело → `import_page_markdown`», сохраняющий всё, включая выделения
-  комментариев.
-- **`import_page_markdown`** — Заменить контент страницы из Markdown-файла в диалекте
-  Docmost, созданного `export_page_markdown`, восстанавливая якоря-выделения комментариев и
-  диаграммы из их inline-HTML. (Треды комментариев из файла не пересоздаются на сервере —
-  записываются только тело страницы и inline-марки комментариев; тредами управляйте через
-  инструменты/UI комментариев.)
+  диаграммами и завершающий блок тредов комментариев. Чтобы заменить тело страницы из
+  обычного авторского Markdown, используйте `update_page_markdown`.
+
+> **Удалено в этом релизе:** `import_page_markdown` (парсер round-trip для
+> экспортированного Docmost-Markdown-файла) **больше не отдаётся на внешней MCP-поверхности**.
+> Чтобы заменить тело страницы из Markdown, используйте **`update_page_markdown`** (замена
+> тела обычным Markdown). См. заметку о миграции в CHANGELOG.
 
 ### Изображения
 
@@ -263,7 +266,8 @@ Docmost-MCP не сочетают:
   `delete_node`, адресуя узел по его `attrs.id` из `get_page_json`.
 - **Изображения**: `insert_image` / `replace_image`.
 - **Новая страница**: `create_page`.
-- **Массовая перезапись или узлы без id**: `update_page_json`.
+- **Массовая перезапись или узлы без id**: `update_page_json` (ProseMirror) или
+  `update_page_markdown` (замена тела обычным Markdown).
 - **Многошаговая / скриптовая перезапись** (перенумерация, сноски, согласованные правки):
   `docmost_transform` — предпросмотр через `dryRun`, затем применение.
 - **Скопировать контент целой страницы из другой** (на стороне сервера):
@@ -278,8 +282,8 @@ Docmost-MCP не сочетают:
   → `get_node`.
 - **Таблицы** (добавить/удалить строку, задать ячейку): `table_get` / `table_insert_row` /
   `table_delete_row` / `table_update_cell`.
-- **Round-trip страницы через Markdown** (скачать, отредактировать, залить обратно без
-  потерь, с комментариями): `export_page_markdown` / `import_page_markdown`.
+- **Экспорт страницы в самодостаточный Markdown** (с якорями комментариев): `export_page_markdown`.
+- **Заменить тело страницы из Markdown**: `update_page_markdown`.
 
 ---
 

packages/mcp/src/lib/diff.ts

@@ -14,7 +14,19 @@
  * signature.
  *
  * If recreateTransform / the changeset throws on a pathological document pair,
- * we fall back to a coarse block-level text diff so the tool never hard-fails.
+ * OR the pair is too large to diff cheaply (see the size guard below), we fall
+ * back to a coarse block-level text diff so the tool never hard-fails and never
+ * pins the event loop.
+ *
+ * SIZE GUARD (issue #464 — prod CPU-DoS). recreateTransform computes its diff via
+ * rfc6902.createPatch, whose array diff is O(n·m) Levenshtein per array pair and
+ * whose per-run word diff is O(w²); on a large/heavily-changed doc this runs for
+ * seconds-to-hours and starves the whole process (BullMQ, Redis lock renewals,
+ * embeddings). It never THROWS — it just never finishes — so the try/catch below
+ * cannot save us. Because diffDocs runs on EVERY in-app/MCP content edit's verify
+ * report, we PRE-FLIGHT the doc size and route anything above a cheap cap straight
+ * to the coarse fallback (the same shape the catch produces). Same cap+fallback
+ * pattern as the ELK-layout DoS fix (#440 / c917dcc3).
  */
 
 import { Node } from "@tiptap/pm/model";
@@ -72,6 +84,56 @@ function countNodes(doc: any, pred: (node: any) => boolean): number {
   return n;
 }
 
+// --- Issue #464: pre-flight size guard for the precise diff ------------------
+// Defaults are BENCHMARK-derived on the recreateTransform(complexSteps:false,
+// wordDiffs:true, simplifyDiff:true) pipeline, chosen so the WORST case (a fully
+// re-written doc — the adversarial shape that drove the incident) keeps the
+// synchronous block under ~200ms REGARDLESS of input:
+//   - 150 total nodes: worst-case pair ~176ms; the O(node²) array diff crosses
+//     200ms at ~170 nodes and then explodes super-linearly (400 nodes ~1.3s,
+//     800 ~5.5s), so cap just below the crossover.
+//   - 12 KiB serialized JSON: an independent axis, because the per-run word diff
+//     is O(words²) — a FEW nodes with very long text runs is dangerous even at a
+//     low node count (17 nodes / ~11 KiB ~176ms, / ~14 KiB ~290ms). A node-light
+//     but byte-heavy doc is still refused.
+// Either metric over its cap routes to the coarse fallback. Both are env-tunable
+// for operators who accept more CPU in exchange for exact diffs on larger docs.
+const DEFAULT_MAX_NODES = 150;
+const DEFAULT_MAX_BYTES = 12 * 1024;
+
+/**
+ * Read a positive-integer env override, falling back to `dflt`. Garbage / unset /
+ * non-finite / non-positive all fall back (so the guard can never be accidentally
+ * disabled by a malformed value). Read fresh on every call so a test / operator
+ * can flip the knob without a restart.
+ */
+function readPositiveIntEnv(name: string, dflt: number): number {
+  const raw = parseInt(process.env[name] ?? "", 10);
+  return Number.isFinite(raw) && raw > 0 ? raw : dflt;
+}
+
+/**
+ * True when the pair is too large for the precise (recreateTransform) diff and
+ * must degrade to the coarse fallback. Takes the MAX of the two docs on each
+ * metric so an ASYMMETRIC pair (a small new doc vs a huge old doc, or vice
+ * versa) — which still explodes rfc6902 — is caught. Cheap: one node walk +
+ * one JSON.stringify per doc, both O(size).
+ */
+function exceedsDiffSizeGuard(oldDoc: any, newDoc: any): boolean {
+  const maxNodes = readPositiveIntEnv("MCP_DIFF_MAX_NODES", DEFAULT_MAX_NODES);
+  const maxBytes = readPositiveIntEnv("MCP_DIFF_MAX_BYTES", DEFAULT_MAX_BYTES);
+  const nodes = Math.max(
+    countNodes(oldDoc, () => true),
+    countNodes(newDoc, () => true),
+  );
+  if (nodes > maxNodes) return true;
+  const bytes = Math.max(
+    JSON.stringify(oldDoc)?.length ?? 0,
+    JSON.stringify(newDoc)?.length ?? 0,
+  );
+  return bytes > maxBytes;
+}
+
 /**
  * Count UNIQUE links in a JSON doc by their `href`. A single link can be split
  * across several adjacent text runs (e.g. a "link+bold" run followed by a "link"
@@ -226,6 +288,81 @@ function coarseDiff(oldDoc: any, newDoc: any): DiffChange[] {
   return changes;
 }
 
+/** Accumulated textual changes plus their derived char/block tallies. */
+interface DiffTally {
+  changes: DiffChange[];
+  inserted: number;
+  deleted: number;
+  changedBlocks: Set<string>;
+}
+
+/**
+ * Produce the coarse-fallback tally for a pair. This is the SINGLE source of the
+ * `fellBack:true` result shape, shared by BOTH degrade paths in diffDocs (the
+ * pre-flight size guard and the recreateTransform catch) so they behave and
+ * report identically.
+ */
+function coarseDiffTally(oldDoc: any, newDoc: any): DiffTally {
+  const changes = coarseDiff(oldDoc, newDoc);
+  let inserted = 0;
+  let deleted = 0;
+  const changedBlocks = new Set<string>();
+  for (const c of changes) {
+    if (c.op === "insert") inserted += c.text.length;
+    else deleted += c.text.length;
+    if (c.block) changedBlocks.add(c.op[0] + ":" + c.block);
+  }
+  return { changes, inserted, deleted, changedBlocks };
+}
+
+/**
+ * Compute the PRECISE tally via the recreateTransform pipeline. Callers MUST
+ * gate this behind the size guard (it can block the event loop for a large pair)
+ * and wrap it in try/catch (a pathological pair can throw); on either the guard
+ * or a throw, use `coarseDiffTally` instead. Kept as a sibling of
+ * `coarseDiffTally` so both produce the same `DiffTally` shape.
+ */
+function preciseDiffTally(oldDocJson: any, newDocJson: any): DiffTally {
+  const oldNode = Node.fromJSON(docmostSchema, oldDocJson);
+  const newNode = Node.fromJSON(docmostSchema, newDocJson);
+  const tr = recreateTransform(oldNode, newNode, {
+    complexSteps: false,
+    wordDiffs: true,
+    simplifyDiff: true,
+  });
+  const changeSet = ChangeSet.create(oldNode).addSteps(tr.doc, tr.mapping.maps, []);
+  const simplified = simplifyChanges(changeSet.changes, newNode);
+
+  const changes: DiffChange[] = [];
+  let inserted = 0;
+  let deleted = 0;
+  const changedBlocks = new Set<string>();
+
+  for (const change of simplified) {
+    // Deleted text lives in the OLD doc coordinate range [fromA, toA).
+    if (change.toA > change.fromA) {
+      const text = oldNode.textBetween(change.fromA, change.toA, "\n", " ");
+      if (text.length > 0) {
+        deleted += text.length;
+        const block = blockContextAt(oldNode, change.fromA);
+        changes.push({ op: "delete", block, text });
+        if (block) changedBlocks.add("d:" + block);
+      }
+    }
+    // Inserted text lives in the NEW doc coordinate range [fromB, toB).
+    if (change.toB > change.fromB) {
+      const text = newNode.textBetween(change.fromB, change.toB, "\n", " ");
+      if (text.length > 0) {
+        inserted += text.length;
+        const block = blockContextAt(newNode, change.fromB);
+        changes.push({ op: "insert", block, text });
+        if (block) changedBlocks.add("i:" + block);
+      }
+    }
+  }
+  return { changes, inserted, deleted, changedBlocks };
+}
+
 /** Build the human-readable unified-ish markdown summary. */
 function renderMarkdown(
   result: Omit<DiffResult, "markdown">,
@@ -276,66 +413,39 @@ export function diffDocs(
   newDocJson: any,
   notesHeading: string = "Примечания переводчика",
 ): DiffResult {
+  // computeIntegrity is cheap (linear node walks) and its counts are needed in
+  // BOTH the precise and coarse paths, so it always runs first.
   const integrity = computeIntegrity(oldDocJson, newDocJson, notesHeading);
 
-  let changes: DiffChange[] = [];
-  let inserted = 0;
-  let deleted = 0;
   let fellBack = false;
-  const changedBlocks = new Set<string>();
+  let tally: DiffTally;
 
-  try {
-    const oldNode = Node.fromJSON(docmostSchema, oldDocJson);
-    const newNode = Node.fromJSON(docmostSchema, newDocJson);
-    const tr = recreateTransform(oldNode, newNode, {
-      complexSteps: false,
-      wordDiffs: true,
-      simplifyDiff: true,
-    });
-    const changeSet = ChangeSet.create(oldNode).addSteps(
-      tr.doc,
-      tr.mapping.maps,
-      [],
-    );
-    const simplified = simplifyChanges(changeSet.changes, newNode);
-
-    for (const change of simplified) {
-      // Deleted text lives in the OLD doc coordinate range [fromA, toA).
-      if (change.toA > change.fromA) {
-        const text = oldNode.textBetween(change.fromA, change.toA, "\n", " ");
-        if (text.length > 0) {
-          deleted += text.length;
-          const block = blockContextAt(oldNode, change.fromA);
-          changes.push({ op: "delete", block, text });
-          if (block) changedBlocks.add("d:" + block);
-        }
-      }
-      // Inserted text lives in the NEW doc coordinate range [fromB, toB).
-      if (change.toB > change.fromB) {
-        const text = newNode.textBetween(change.fromB, change.toB, "\n", " ");
-        if (text.length > 0) {
-          inserted += text.length;
-          const block = blockContextAt(newNode, change.fromB);
-          changes.push({ op: "insert", block, text });
-          if (block) changedBlocks.add("i:" + block);
-        }
-      }
-    }
-  } catch {
-    // Pathological pair: degrade to a coarse block-level diff so we never throw.
+  // Pre-flight size guard (#464): a too-large pair would make recreateTransform
+  // block the event loop for seconds-to-hours WITHOUT throwing, so route it to
+  // the coarse fallback BEFORE calling recreateTransform at all. Both this path
+  // and the catch below go through coarseDiffTally for an identical `fellBack`
+  // result shape.
+  if (exceedsDiffSizeGuard(oldDocJson, newDocJson)) {
     fellBack = true;
-    changes = coarseDiff(oldDocJson, newDocJson);
-    for (const c of changes) {
-      if (c.op === "insert") inserted += c.text.length;
-      else deleted += c.text.length;
-      if (c.block) changedBlocks.add(c.op[0] + ":" + c.block);
+    tally = coarseDiffTally(oldDocJson, newDocJson);
+  } else {
+    try {
+      tally = preciseDiffTally(oldDocJson, newDocJson);
+    } catch {
+      // Pathological pair: degrade to a coarse block-level diff so we never throw.
+      fellBack = true;
+      tally = coarseDiffTally(oldDocJson, newDocJson);
     }
   }
 
   const partial: Omit<DiffResult, "markdown"> = {
-    summary: { inserted, deleted, blocksChanged: changedBlocks.size },
+    summary: {
+      inserted: tally.inserted,
+      deleted: tally.deleted,
+      blocksChanged: tally.changedBlocks.size,
+    },
     integrity,
-    changes,
+    changes: tally.changes,
   };
   return { ...partial, markdown: renderMarkdown(partial, fellBack) };
 }

packages/mcp/src/server-instructions.ts

@@ -41,10 +41,10 @@ import { SHARED_TOOL_SPECS, SharedToolSpec } from "./tool-specs.js";
 export const ROUTING_PROSE =
   "Docmost editing guide — choose the tool by intent. The <tool_inventory> at the end lists every tool with a one-line purpose; the notes below are the routing hints for WHEN to reach for each.\n" +
   "READ: find a page -> search (workspace-wide full-text); list -> list_pages / list_spaces. Locate blocks and their ids CHEAPLY -> get_outline (compact top-level map; start here, not get_page_json). One block's subtree -> get_node (by attrs.id, or \"#<index>\" for tables, which carry no id). Find every occurrence of a string/regex ON a page (and where each is) -> search_in_page, NOT block-by-block get_node — it returns each hit's node ref + block index + context for a targeted comment. Whole page -> get_page (Markdown, lossy; inline <span data-comment-id> tags are comment anchors — markup, not text) or get_page_json (lossless ProseMirror with block ids). Hand a huge page (with images) to an external consumer without pulling it through the model context -> stash_page (returns a short-lived anonymous URL).\n" +
-  "EDIT: fix wording/typos/numbers -> edit_page_text (find/replace inside blocks, no node id needed). Change ONE block (paragraph/heading/callout/etc.) structurally -> patch_node (by attrs.id from get_outline). Add a block -> insert_node (before/after a block by attrs.id or by anchor text, or append). Remove a block -> delete_node (by attrs.id). Tables -> table_get / table_update_cell / table_insert_row / table_delete_row (address by \"#<index>\" from get_outline; table nodes have no attrs.id). Images -> insert_image (add from a web URL) / replace_image (swap an existing image). Draw.io diagrams -> drawio_create (create from mxGraph XML and insert), drawio_get (read a diagram as mxGraph XML + a hash), drawio_update (replace a diagram; pass the hash from drawio_get as baseHash for optimistic locking); before authoring a diagram, drawio_shapes (look up verified stencil style-strings so a shape name never renders as an empty box) and drawio_guide (on-demand authoring reference: skeleton/layout/containers/icons-aws/icons-azure), and pass layout:\"elk\" to drawio_create/drawio_update to auto-place nodes. Footnotes -> insert_footnote. Bulk/structural rewrite -> update_page_json (full ProseMirror replace; prefer the granular tools above to avoid resending the whole ~100KB+ document). Complex/scripted rewrite (multiple coordinated edits, renumbering) -> docmost_transform: write a JS `(doc, ctx) => doc` transform, preview the diff with dryRun (default), then apply with dryRun:false; ctx.helpers includes commentsToFootnotes for turning inline comments into numbered footnotes.\n" +
+  "EDIT: fix wording/typos/numbers -> edit_page_text (find/replace inside blocks, no node id needed). Change ONE block (paragraph/heading/callout/etc.) structurally -> patch_node (by attrs.id from get_outline). Add a block -> insert_node (before/after a block by attrs.id or by anchor text, or append). Remove a block -> delete_node (by attrs.id). Tables -> table_get / table_update_cell / table_insert_row / table_delete_row (address by \"#<index>\" from get_outline; table nodes have no attrs.id). Images -> insert_image (add from a web URL) / replace_image (swap an existing image). Draw.io diagrams -> drawio_create (create from mxGraph XML and insert), drawio_get (read a diagram as mxGraph XML + a hash), drawio_update (replace a diagram; pass the hash from drawio_get as baseHash for optimistic locking); before authoring a diagram, drawio_shapes (look up verified stencil style-strings so a shape name never renders as an empty box) and drawio_guide (on-demand authoring reference: skeleton/layout/containers/icons-aws/icons-azure), and pass layout:\"elk\" to drawio_create/drawio_update to auto-place nodes. Footnotes -> insert_footnote. Bulk/structural rewrite -> update_page_json (full ProseMirror replace) or update_page_markdown (full plain-Markdown body replace, re-imported — block ids regenerate); prefer the granular tools above to avoid resending the whole ~100KB+ document. Complex/scripted rewrite (multiple coordinated edits, renumbering) -> docmost_transform: write a JS `(doc, ctx) => doc` transform, preview the diff with dryRun (default), then apply with dryRun:false; ctx.helpers includes commentsToFootnotes for turning inline comments into numbered footnotes.\n" +
   "PAGES: new -> create_page (Markdown). Rename (title only) -> rename_page. Move -> move_page. Delete -> delete_page (SOFT delete — the page goes to trash and is restorable; nothing is permanent). Copy/replace a page's whole content from another page (server-side, no document through the model) -> copy_page_content. Sharing -> share_page / unshare_page / list_shares; share_page makes the page PUBLICLY accessible — do it only when explicitly asked.\n" +
   "COMMENTS: create_comment is always inline and requires an EXACT selection — contiguous text from a single block, <=250 chars (fails rather than leaving an unanchored comment); reply to a thread via parentCommentId. Propose a concrete text fix for one-click human approval -> create_comment with suggestedText (the exact plain-text replacement for the selection; the selection must then be UNIQUE in the page — extend it with context if needed); prefer this over editing directly when the change is subjective or needs the author's sign-off. Manage -> list_comments, update_comment, resolve_comment (resolve/reopen, reversible — prefer over delete to close), delete_comment, check_new_comments.\n" +
-  "HISTORY: review what changed -> diff_page_versions (a historyId vs current, or two versions). List saved versions -> list_page_history. Undo a bad edit -> restore_page_version (writes a past version back as current; itself revertible). Lossless markdown round-trip (download, edit, re-upload, incl. comment anchors) -> export_page_markdown / import_page_markdown.";
+  "HISTORY: review what changed -> diff_page_versions (a historyId vs current, or two versions). List saved versions -> list_page_history. Undo a bad edit -> restore_page_version (writes a past version back as current; itself revertible). Export a page to self-contained Docmost Markdown (with comment anchors) -> export_page_markdown.";
 
 /**
  * A single generated inventory line: the tool's registered NAME + a one-line
@@ -96,6 +96,7 @@ const TOOL_FAMILY: Record<string, Family> = {
   insert_node: "EDIT",
   delete_node: "EDIT",
   update_page_json: "EDIT",
+  update_page_markdown: "EDIT",
   table_get: "EDIT",
   table_update_cell: "EDIT",
   table_insert_row: "EDIT",
@@ -130,7 +131,8 @@ const TOOL_FAMILY: Record<string, Family> = {
   list_page_history: "HISTORY",
   restore_page_version: "HISTORY",
   export_page_markdown: "HISTORY",
-  import_page_markdown: "HISTORY",
+  // import_page_markdown is now inAppOnly (#411) — it is not registered on the
+  // external MCP host, so it no longer appears in the generated inventory.
 };
 
 /**

packages/mcp/src/tool-specs.ts

@@ -81,6 +81,7 @@ export type DocmostClientLike = Pick<
   | 'patchNode'
   | 'insertNode'
   | 'deleteNode'
+  | 'updatePage'
   | 'updatePageJson'
   | 'tableInsertRow'
   | 'tableDeleteRow'
@@ -642,6 +643,12 @@ export const SHARED_TOOL_SPECS = {
   importPageMarkdown: {
     mcpName: 'import_page_markdown',
     inAppKey: 'importPageMarkdown',
+    // IN-APP ONLY (issue #411): the external /mcp surface no longer exposes
+    // import_page_markdown — the registry loop in index.ts skips inAppOnly specs,
+    // so this stays available to the in-app agent (round-tripping an EXPORTED
+    // Docmost-Markdown file) but is removed from the public MCP tool set. Plain
+    // authoring-markdown body replace on the MCP surface is update_page_markdown.
+    inAppOnly: true,
     description:
       "Replace a page's content from a self-contained Docmost-flavoured " +
       'Markdown file produced by the page-Markdown export tool. Restores comment ' +
@@ -1119,6 +1126,51 @@ export const SHARED_TOOL_SPECS = {
     },
   },
 
+  // Full-body replace from PLAIN Markdown (issue #411). Pairs with
+  // updatePageJson (which takes a ProseMirror document): this one takes a
+  // markdown string and re-imports the whole body. `client.updatePage` runs it
+  // through updatePageContentRealtime -> markdownToProseMirrorCanonical, so
+  // Docmost-flavoured markdown (incl. `^[...]` inline footnotes) is parsed and
+  // canonicalized. Distinct from importPageMarkdown, which re-imports a
+  // self-contained EXPORTED Docmost-Markdown file (with comment anchors +
+  // diagrams); this tool takes ordinary authoring markdown. Shared spec, so the
+  // registry loop registers it on BOTH hosts (external MCP + in-app agent) —
+  // #411 replaced the old inline in-app `updatePageContent` tool with this.
+  updatePageMarkdown: {
+    // snake_case for now; camelCase public MCP naming is the next issue (#412).
+    mcpName: 'update_page_markdown',
+    inAppKey: 'updatePageMarkdown',
+    description:
+      "Replace a page's body with new Markdown content (and optionally its " +
+      'title). The whole body is re-imported from the markdown (block ids ' +
+      'regenerate — for surgical or id-preserving edits use the find/replace, ' +
+      'node-patch or page-JSON tools instead). Docmost-flavoured markdown is ' +
+      'parsed, including `^[...]` inline footnotes. Reversible: the previous ' +
+      'version is kept in page history.',
+    tier: 'deferred',
+    catalogLine:
+      "updatePageMarkdown — replace a page's body (and optionally title) with new Markdown.",
+    buildShape: (z) => ({
+      pageId: z.string().min(1).describe('The id of the page to update.'),
+      content: z.string().describe('The new page body as Markdown.'),
+      title: z
+        .string()
+        .optional()
+        .describe('Optional new title for the page.'),
+    }),
+    // Single canonical execute on BOTH hosts (the tool was in-app only before,
+    // so there is no external-MCP behavior to preserve). NOTE (rename #411): the
+    // old inline in-app tool projected the client result to { pageId, updated };
+    // the registry now returns the raw client result { success, modified,
+    // message, pageId, verify? } instead. Deliberate: no code reads the removed
+    // `.updated` field, the raw result is strictly more informative to the model
+    // (it surfaces footnote/verify warnings), and it matches the on-both-hosts
+    // registry convention. The result-shape change is the ONLY behavior delta of
+    // this rename; the write path (updatePage -> markdown canonicalize) is identical.
+    execute: (client, { pageId, content, title }) =>
+      client.updatePage(pageId as string, content as string, title as string | undefined),
+  },
+
   exportPageMarkdown: {
     mcpName: 'export_page_markdown',
     inAppKey: 'exportPageMarkdown',

packages/mcp/test/mock/full-doc-write-canonicalize.test.mjs

@@ -3,7 +3,7 @@
 // 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').
+// server-side focus specs for createPage / updatePage (markdown 'replace').
 import { test } from "node:test";
 import assert from "node:assert/strict";
 import { DocmostClient } from "../../build/client.js";

packages/mcp/test/unit/diff-guard-skips-recreate.test.mjs

@@ -0,0 +1,86 @@
+// Issue #464 — prove the size guard SKIPS the recreateTransform pipeline over
+// the cap, not merely that it returns "coarse". node:test's mock.module needs an
+// experimental flag the suite does not pass, so instead of a module spy we use a
+// deterministic BEHAVIORAL proxy that isolates the one variable — the guard:
+//
+//   Same over-cap pair, run twice:
+//     (a) default caps            -> guard trips  -> recreateTransform skipped,
+//     (b) caps raised above the doc -> guard OFF -> recreateTransform DOES run.
+//
+// The only code path that differs between (a) and (b) is whether
+// recreateTransform executes. recreateTransform on this pair is O(n²) and takes
+// SECONDS; the guarded path is a linear coarse diff taking milliseconds. So a
+// large (a)≪(b) time ratio can ONLY be explained by (a) skipping the transform.
+// This asserts the skip without depending on mock.module.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { diffDocs } from "../../build/lib/diff.js";
+
+const t = (text) => ({ type: "text", text });
+const para = (text) => ({ type: "paragraph", content: text ? [t(text)] : [] });
+const doc = (children) => ({ type: "doc", content: children });
+function buildDoc(n, seed) {
+  return doc(
+    Array.from({ length: n }, (_, i) =>
+      para(Array.from({ length: 8 }, (_, w) => `${seed}${i}_${w}`).join(" ")),
+    ),
+  );
+}
+function clearEnv() {
+  delete process.env.MCP_DIFF_MAX_NODES;
+  delete process.env.MCP_DIFF_MAX_BYTES;
+}
+function timed(fn) {
+  const s = performance.now();
+  const out = fn();
+  return { out, ms: performance.now() - s };
+}
+
+// A 300-para (~600-node) pair: comfortably over the 150-node default, yet small
+// enough that the un-guarded recreateTransform still FINISHES (~1-3s) so the
+// test can time the contrast without hanging.
+const OLD = buildDoc(300, "a");
+const NEW = buildDoc(300, "b");
+
+test("guard skips recreateTransform over-cap (guarded run is far faster than un-guarded)", () => {
+  // (a) Guarded: default caps -> should short-circuit to coarse, near-instant.
+  clearEnv();
+  const guarded = timed(() => diffDocs(OLD, NEW));
+  assert.match(
+    guarded.out.markdown,
+    /coarse block-level diff/,
+    "guarded run must be coarse (guard tripped)",
+  );
+
+  // (b) Un-guarded: raise both caps above the doc so the precise path runs.
+  process.env.MCP_DIFF_MAX_NODES = "1000000";
+  process.env.MCP_DIFF_MAX_BYTES = "100000000";
+  let unguarded;
+  try {
+    unguarded = timed(() => diffDocs(OLD, NEW));
+  } finally {
+    clearEnv();
+  }
+  assert.doesNotMatch(
+    unguarded.out.markdown,
+    /coarse block-level diff/,
+    "with caps raised, the precise recreateTransform path runs",
+  );
+
+  // The precise run executed recreateTransform (O(n²)); the guarded run did not.
+  // Require a large speedup so the ONLY explanation is the skipped transform.
+  assert.ok(
+    guarded.ms * 5 < unguarded.ms,
+    `guarded (${guarded.ms.toFixed(1)}ms) must be >=5x faster than un-guarded ` +
+      `(${unguarded.ms.toFixed(1)}ms); a small gap would mean the transform still ran`,
+  );
+});
+
+test("guarded over-cap call stays within the ~200ms event-loop budget", () => {
+  clearEnv();
+  // Best-of-3 to shed GC/JIT noise; the guarded coarse path is a linear walk.
+  let best = Infinity;
+  for (let i = 0; i < 3; i++) best = Math.min(best, timed(() => diffDocs(OLD, NEW)).ms);
+  assert.ok(best < 200, `guarded over-cap diff must be <200ms, was ${best.toFixed(1)}ms`);
+});

packages/mcp/test/unit/diff-size-guard.test.mjs

@@ -0,0 +1,229 @@
+// Issue #464 — prod CPU-DoS pre-flight size guard for diffDocs.
+//
+// diffDocs synchronously calls recreateTransform (rfc6902) which is O(n·m) in
+// node count and O(w²) in per-run word count; on a large/heavily-changed doc it
+// pins the event loop for seconds-to-hours WITHOUT throwing. A pre-flight size
+// guard routes any doc over MCP_DIFF_MAX_NODES / MCP_DIFF_MAX_BYTES straight to
+// the coarse fallback (`fellBack:true`), so the sync block stays ~<200ms.
+//
+// These tests assert the BEHAVIOR of the guard (fast + coarse-mode + asymmetry +
+// env knobs). A sibling test (diff-guard-skips-recreate.test.mjs) proves
+// recreateTransform is skipped over the cap via a behavioral proxy (guarded run
+// is orders of magnitude faster than the same pair with the caps raised).
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { diffDocs } from "../../build/lib/diff.js";
+
+// ---------------------------------------------------------------------------
+// Builders
+// ---------------------------------------------------------------------------
+const t = (text) => ({ type: "text", text });
+const para = (text) => ({ type: "paragraph", content: text ? [t(text)] : [] });
+const doc = (children) => ({ type: "doc", content: children });
+
+/** A doc of `n` paragraphs whose words are seeded from `seed` (fully changeable). */
+function buildDoc(n, wordsPerPara, seed) {
+  const blocks = [];
+  for (let i = 0; i < n; i++) {
+    const words = [];
+    for (let w = 0; w < wordsPerPara; w++) words.push(`${seed}${i}_${w}`);
+    blocks.push(para(words.join(" ")));
+  }
+  return doc(blocks);
+}
+
+/** Reset the env knobs to their unset default between tests. */
+function clearEnv() {
+  delete process.env.MCP_DIFF_MAX_NODES;
+  delete process.env.MCP_DIFF_MAX_BYTES;
+}
+
+// ---------------------------------------------------------------------------
+// Over-threshold (by node count) -> FAST + coarse mode.
+// A fully re-written 600-para doc is the worst case that drove the incident;
+// with the guard it must return in well under the ~200ms budget and in coarse
+// mode. Without the guard this single call takes multiple SECONDS.
+// ---------------------------------------------------------------------------
+test("over-threshold doc falls back to coarse mode and returns fast", () => {
+  clearEnv();
+  // 600 paragraphs -> ~1200 nodes, far over the 150-node default.
+  const oldDoc = buildDoc(600, 8, "a");
+  const newDoc = buildDoc(600, 8, "b");
+
+  const start = performance.now();
+  const r = diffDocs(oldDoc, newDoc);
+  const elapsed = performance.now() - start;
+
+  // Coarse mode is signalled in the markdown note (fellBack path).
+  assert.match(
+    r.markdown,
+    /coarse block-level diff/,
+    "over-threshold pair must use the coarse fallback",
+  );
+  // Budget: the guard makes this near-instant. Generous 1s ceiling to avoid CI
+  // flake while still being ~10x under the multi-second un-guarded cost.
+  assert.ok(
+    elapsed < 1000,
+    `expected fast coarse fallback, took ${elapsed.toFixed(0)}ms`,
+  );
+  // Coarse diff still detects the wholesale change.
+  assert.ok(r.summary.inserted > 0 || r.summary.deleted > 0, "reports changes");
+});
+
+// ---------------------------------------------------------------------------
+// Under-threshold (small) doc -> precise diff, NOT coarse mode. No regression.
+// ---------------------------------------------------------------------------
+test("under-threshold doc uses the precise diff (no fallback note)", () => {
+  clearEnv();
+  const oldDoc = doc([para("Hello world")]);
+  const newDoc = doc([para("Hello brave world")]);
+  const r = diffDocs(oldDoc, newDoc);
+
+  assert.doesNotMatch(
+    r.markdown,
+    /coarse block-level diff/,
+    "a small doc must take the precise path",
+  );
+  // Precise word diff finds exactly the inserted word.
+  const ins = r.changes.find((c) => c.op === "insert");
+  assert.ok(ins && /brave/.test(ins.text), "precise diff isolates the inserted word");
+});
+
+// ---------------------------------------------------------------------------
+// Asymmetry: a small NEW doc vs a huge OLD doc (and vice versa) still explodes
+// rfc6902, so max(old,new) must trip the guard in BOTH directions.
+// ---------------------------------------------------------------------------
+test("asymmetric pair (huge old, tiny new) falls back to coarse", () => {
+  clearEnv();
+  const hugeOld = buildDoc(600, 8, "a");
+  const tinyNew = doc([para("just one line")]);
+  const r = diffDocs(hugeOld, tinyNew);
+  assert.match(r.markdown, /coarse block-level diff/, "huge-old side must trip the guard");
+});
+
+test("asymmetric pair (tiny old, huge new) falls back to coarse", () => {
+  clearEnv();
+  const tinyOld = doc([para("just one line")]);
+  const hugeNew = buildDoc(600, 8, "b");
+  const r = diffDocs(tinyOld, hugeNew);
+  assert.match(r.markdown, /coarse block-level diff/, "huge-new side must trip the guard");
+});
+
+// ---------------------------------------------------------------------------
+// Byte axis: a FEW nodes but a very large serialized size (long text runs) is
+// dangerous too (per-run word diff is O(words²)), so the byte cap must trip
+// independently of the node count.
+// ---------------------------------------------------------------------------
+test("node-light but byte-heavy doc falls back on the byte cap", () => {
+  clearEnv();
+  // 5 paragraphs (~11 nodes, well under the node cap) but each a very long run,
+  // pushing the serialized size far over the 12 KiB byte default.
+  const bigRun = (seed) =>
+    doc(
+      Array.from({ length: 5 }, (_, i) =>
+        para(Array.from({ length: 800 }, (_, w) => `${seed}${i}_${w}`).join(" ")),
+      ),
+    );
+  const oldDoc = bigRun("a");
+  const newDoc = bigRun("b");
+  // Sanity: node count is under the default node cap, so ONLY the byte cap can
+  // be what trips the guard here.
+  const nodeCount = (d) => {
+    let n = 0;
+    const v = (x) => {
+      if (!x || typeof x !== "object") return;
+      n++;
+      if (Array.isArray(x.content)) for (const c of x.content) v(c);
+    };
+    v(d);
+    return n;
+  };
+  assert.ok(nodeCount(oldDoc) < 150, "node count is under the node cap");
+  assert.ok(JSON.stringify(oldDoc).length > 12 * 1024, "serialized size is over the byte cap");
+
+  const r = diffDocs(oldDoc, newDoc);
+  assert.match(r.markdown, /coarse block-level diff/, "byte cap must trip independently");
+});
+
+// ---------------------------------------------------------------------------
+// Env override: a very low MCP_DIFF_MAX_NODES forces fallback on a tiny doc,
+// proving the knob is read fresh and actually gates the diff.
+// ---------------------------------------------------------------------------
+test("MCP_DIFF_MAX_NODES override forces fallback on a small doc", () => {
+  clearEnv();
+  const oldDoc = doc([para("Hello world")]);
+  const newDoc = doc([para("Hello brave world")]);
+
+  // Baseline: default caps -> precise diff.
+  assert.doesNotMatch(diffDocs(oldDoc, newDoc).markdown, /coarse block-level diff/);
+
+  // Knob set absurdly low -> even this 4-node doc trips the guard.
+  process.env.MCP_DIFF_MAX_NODES = "1";
+  try {
+    const r = diffDocs(oldDoc, newDoc);
+    assert.match(r.markdown, /coarse block-level diff/, "low node cap forces fallback");
+  } finally {
+    clearEnv();
+  }
+});
+
+test("MCP_DIFF_MAX_BYTES override forces fallback on a small doc", () => {
+  clearEnv();
+  const oldDoc = doc([para("Hello world")]);
+  const newDoc = doc([para("Hello brave world")]);
+
+  process.env.MCP_DIFF_MAX_BYTES = "1";
+  try {
+    const r = diffDocs(oldDoc, newDoc);
+    assert.match(r.markdown, /coarse block-level diff/, "low byte cap forces fallback");
+  } finally {
+    clearEnv();
+  }
+});
+
+// ---------------------------------------------------------------------------
+// Garbage / unset env values fall back to the DEFAULT (the guard can never be
+// accidentally disabled by a malformed knob). A small doc must still diff
+// precisely under a garbage cap.
+// ---------------------------------------------------------------------------
+test("garbage env values fall back to the default cap (guard not disabled)", () => {
+  clearEnv();
+  const oldDoc = doc([para("Hello world")]);
+  const newDoc = doc([para("Hello brave world")]);
+
+  for (const bad of ["not-a-number", "0", "-5", "", "NaN", "1e999"]) {
+    process.env.MCP_DIFF_MAX_NODES = bad;
+    process.env.MCP_DIFF_MAX_BYTES = bad;
+    // Under the DEFAULT caps this small doc is precise (garbage did not raise
+    // OR disable the cap). "1e999" -> parseInt yields 1 (finite) which is a
+    // valid low cap and would fall back; exclude that from the precise check.
+    const r = diffDocs(oldDoc, newDoc);
+    if (bad === "1e999") {
+      // parseInt("1e999",10) === 1 -> a legit low cap -> fallback. Guard active.
+      assert.match(r.markdown, /coarse block-level diff/);
+    } else {
+      assert.doesNotMatch(
+        r.markdown,
+        /coarse block-level diff/,
+        `garbage value ${JSON.stringify(bad)} must fall back to the default cap`,
+      );
+    }
+  }
+  clearEnv();
+});
+
+// ---------------------------------------------------------------------------
+// A large doc that trips the guard must still return the correct INTEGRITY
+// counts (computeIntegrity runs before the diff and is unaffected by fallback).
+// ---------------------------------------------------------------------------
+test("integrity counts are still correct on a guard-tripped (coarse) doc", () => {
+  clearEnv();
+  const image = { type: "image", attrs: { src: "/api/files/a.png" } };
+  const oldDoc = doc([image, ...buildDoc(600, 8, "a").content]);
+  const newDoc = doc([...buildDoc(600, 8, "b").content]); // image removed
+
+  const r = diffDocs(oldDoc, newDoc);
+  assert.match(r.markdown, /coarse block-level diff/, "large pair fell back");
+  assert.deepEqual(r.integrity.images, [1, 0], "integrity is computed regardless of fallback");
+});

packages/mcp/test/unit/tool-inventory.test.mjs

@@ -27,7 +27,8 @@ const SRC = join(HERE, "..", "..", "src");
 /**
  * Every tool name the MCP server registers, scraped from the SOURCE:
  *  - inline `server.registerTool("name", ...)` calls in index.ts;
- *  - shared specs in tool-specs.ts (`mcpName: 'name'`).
+ *  - shared specs in tool-specs.ts (`mcpName: 'name'`), EXCEPT `inAppOnly`
+ *    specs, which the registry loop in index.ts SKIPS on the MCP host (#411).
  * Same two registration mechanisms the old guard covered.
  */
 function registeredToolNames() {
@@ -37,8 +38,13 @@ function registeredToolNames() {
   for (const m of indexSrc.matchAll(/registerTool\(\s*"([a-z0-9_]+)"/g)) {
     names.add(m[1]);
   }
-  for (const m of specsSrc.matchAll(/mcpName:\s*['"]([a-z0-9_]+)['"]/g)) {
-    names.add(m[1]);
+  // Each spec is one `{ ... }` block; scrape its mcpName but skip a block that
+  // carries `inAppOnly: true` (not registered on the external MCP host).
+  for (const block of specsSrc.split(/\n\s{2}\w+:\s*\{/)) {
+    const nameMatch = block.match(/mcpName:\s*['"]([a-z0-9_]+)['"]/);
+    if (!nameMatch) continue;
+    if (/inAppOnly:\s*true/.test(block)) continue;
+    names.add(nameMatch[1]);
   }
   return names;
 }
@@ -76,6 +82,30 @@ test("the inventory has no phantom tool (every line is a real registered tool)",
   );
 });
 
+// #411: the external MCP surface gains update_page_markdown and LOSES
+// import_page_markdown (now inAppOnly). The in-app agent still keeps
+// importPageMarkdown — asserted in the server-side contract spec.
+test("update_page_markdown is on the MCP surface; import_page_markdown is NOT", () => {
+  const inventory = new Set(buildToolInventoryLines().map((l) => l.name));
+  assert.ok(
+    inventory.has("update_page_markdown"),
+    "update_page_markdown should be registered on the external MCP surface",
+  );
+  assert.ok(
+    !inventory.has("import_page_markdown"),
+    "import_page_markdown must be dropped from the external MCP surface (#411)",
+  );
+  // And the routing prose no longer points MCP clients at it.
+  assert.ok(
+    !ROUTING_PROSE.includes("import_page_markdown"),
+    "ROUTING_PROSE still mentions the removed import_page_markdown",
+  );
+  assert.ok(
+    ROUTING_PROSE.includes("update_page_markdown"),
+    "ROUTING_PROSE should mention update_page_markdown",
+  );
+});
+
 test("every inventory line has a non-empty purpose", () => {
   for (const line of buildToolInventoryLines()) {
     assert.equal(typeof line.purpose, "string");

packages/mcp/test/unit/tool-specs.test.mjs

@@ -145,3 +145,36 @@ test("no-arg specs (getWorkspace/listSpaces/listShares) omit buildShape", () =>
     assert.equal(SHARED_TOOL_SPECS[key].buildShape, undefined, `${key} should be no-arg`);
   }
 });
+
+// #411: plain-Markdown full-body replace tool, paired with updatePageJson.
+test("updatePageMarkdown spec exists, pairs with updatePageJson, builds { pageId, content, title }", () => {
+  const spec = SHARED_TOOL_SPECS.updatePageMarkdown;
+  assert.ok(spec, "updatePageMarkdown spec missing");
+  assert.equal(spec.mcpName, "update_page_markdown");
+  assert.equal(spec.inAppKey, "updatePageMarkdown");
+  // Registered on BOTH hosts (a shared spec, no inAppOnly/mcpOnly flag).
+  assert.notEqual(spec.inAppOnly, true);
+  assert.notEqual(spec.mcpOnly, true);
+  // Same tier as its JSON sibling.
+  assert.equal(spec.tier, SHARED_TOOL_SPECS.updatePageJson.tier);
+  const shape = spec.buildShape(z);
+  assert.deepEqual(Object.keys(shape).sort(), ["content", "pageId", "title"]);
+  // pageId + content required, title optional.
+  const schema = z.object(shape);
+  assert.doesNotThrow(() => schema.parse({ pageId: "p1", content: "# Hi" }));
+  assert.throws(() => schema.parse({ pageId: "p1" }));
+  // The description must flag the `^[...]` inline-footnote parse path so the
+  // markdown->footnote canonicalization guarantee stays documented (#411).
+  assert.match(spec.description, /\^\[/);
+});
+
+// #411: import_page_markdown is dropped from the EXTERNAL MCP surface but stays
+// available to the in-app agent — encoded as inAppOnly on the shared spec.
+test("importPageMarkdown spec is inAppOnly (removed from the external MCP surface, kept in-app)", () => {
+  const spec = SHARED_TOOL_SPECS.importPageMarkdown;
+  assert.ok(spec, "importPageMarkdown spec missing");
+  assert.equal(spec.inAppOnly, true);
+  // The spec + its client method are NOT deleted — only hidden from the MCP host.
+  assert.equal(spec.mcpName, "import_page_markdown");
+  assert.equal(spec.inAppKey, "importPageMarkdown");
+});