diff --git a/packages/mcp/build/lib/auth-utils.js b/packages/mcp/build/lib/auth-utils.js
index cc61481c..39b91d9d 100644
--- a/packages/mcp/build/lib/auth-utils.js
+++ b/packages/mcp/build/lib/auth-utils.js
@@ -29,6 +29,41 @@ export async function getCollabToken(baseUrl, apiToken) {
         throw error;
     }
 }
+/**
+ * Pure cookie-parsing helper extracted from `performLogin` so the parsing logic
+ * can be unit-tested without performing the login network request. Given the
+ * raw `Set-Cookie` header array from the login response, return the `authToken`
+ * cookie's value.
+ *
+ * Behavior (kept identical to the original inline logic):
+ *  - throws if there is no Set-Cookie header at all;
+ *  - matches the cookie NAME exactly (`authToken`), so a future
+ *    `authTokenRefresh=...` cookie is NOT picked up (a `startsWith` would be);
+ *  - returns everything after the FIRST `=` up to the first `;`, so a base64
+ *    value containing `=` padding is preserved (a naive `split("=")` would
+ *    truncate it);
+ *  - cookie attributes after the first `;` (Path, HttpOnly, Expires, …) are
+ *    ignored;
+ *  - throws if no `authToken` cookie is present.
+ */
+export function extractAuthTokenFromSetCookie(cookies) {
+    if (!cookies) {
+        throw new Error("No Set-Cookie header found in login response");
+    }
+    // Match the cookie name exactly to avoid matching a future
+    // authTokenRefresh cookie (startsWith would catch it).
+    const authCookie = cookies.find((c) => {
+        const kv = c.split(";")[0];
+        return kv.slice(0, kv.indexOf("=")) === "authToken";
+    });
+    if (!authCookie) {
+        throw new Error("No authToken cookie found in login response");
+    }
+    // Take everything after the FIRST "=" up to the first ";".
+    // Splitting on "=" would truncate base64 values containing "=" padding.
+    const kv = authCookie.split(";")[0];
+    return kv.slice(kv.indexOf("=") + 1);
+}
 export async function performLogin(baseUrl, email, password) {
     try {
         const response = await axios.post(`${baseUrl}/auth/login`, {
@@ -36,24 +71,7 @@ export async function performLogin(baseUrl, email, password) {
             password,
         });
         // Extract token from Set-Cookie header
-        const cookies = response.headers["set-cookie"];
-        if (!cookies) {
-            throw new Error("No Set-Cookie header found in login response");
-        }
-        // Match the cookie name exactly to avoid matching a future
-        // authTokenRefresh cookie (startsWith would catch it).
-        const authCookie = cookies.find((c) => {
-            const kv = c.split(";")[0];
-            return kv.slice(0, kv.indexOf("=")) === "authToken";
-        });
-        if (!authCookie) {
-            throw new Error("No authToken cookie found in login response");
-        }
-        // Take everything after the FIRST "=" up to the first ";".
-        // Splitting on "=" would truncate base64 values containing "=" padding.
-        const kv = authCookie.split(";")[0];
-        const token = kv.slice(kv.indexOf("=") + 1);
-        return token;
+        return extractAuthTokenFromSetCookie(response.headers["set-cookie"]);
     }
     catch (error) {
         // Avoid leaking the full server response body by default; log only the
diff --git a/packages/mcp/src/lib/auth-utils.ts b/packages/mcp/src/lib/auth-utils.ts
index d677be25..a3a3b652 100644
--- a/packages/mcp/src/lib/auth-utils.ts
+++ b/packages/mcp/src/lib/auth-utils.ts
@@ -38,6 +38,45 @@ export async function getCollabToken(
   }
 }
 
+/**
+ * Pure cookie-parsing helper extracted from `performLogin` so the parsing logic
+ * can be unit-tested without performing the login network request. Given the
+ * raw `Set-Cookie` header array from the login response, return the `authToken`
+ * cookie's value.
+ *
+ * Behavior (kept identical to the original inline logic):
+ *  - throws if there is no Set-Cookie header at all;
+ *  - matches the cookie NAME exactly (`authToken`), so a future
+ *    `authTokenRefresh=...` cookie is NOT picked up (a `startsWith` would be);
+ *  - returns everything after the FIRST `=` up to the first `;`, so a base64
+ *    value containing `=` padding is preserved (a naive `split("=")` would
+ *    truncate it);
+ *  - cookie attributes after the first `;` (Path, HttpOnly, Expires, …) are
+ *    ignored;
+ *  - throws if no `authToken` cookie is present.
+ */
+export function extractAuthTokenFromSetCookie(
+  cookies: string[] | undefined,
+): string {
+  if (!cookies) {
+    throw new Error("No Set-Cookie header found in login response");
+  }
+  // Match the cookie name exactly to avoid matching a future
+  // authTokenRefresh cookie (startsWith would catch it).
+  const authCookie = cookies.find((c: string) => {
+    const kv = c.split(";")[0];
+    return kv.slice(0, kv.indexOf("=")) === "authToken";
+  });
+  if (!authCookie) {
+    throw new Error("No authToken cookie found in login response");
+  }
+
+  // Take everything after the FIRST "=" up to the first ";".
+  // Splitting on "=" would truncate base64 values containing "=" padding.
+  const kv = authCookie.split(";")[0];
+  return kv.slice(kv.indexOf("=") + 1);
+}
+
 export async function performLogin(
   baseUrl: string,
   email: string,
@@ -50,25 +89,7 @@ export async function performLogin(
     });
 
     // Extract token from Set-Cookie header
-    const cookies = response.headers["set-cookie"];
-    if (!cookies) {
-      throw new Error("No Set-Cookie header found in login response");
-    }
-    // Match the cookie name exactly to avoid matching a future
-    // authTokenRefresh cookie (startsWith would catch it).
-    const authCookie = cookies.find((c: string) => {
-      const kv = c.split(";")[0];
-      return kv.slice(0, kv.indexOf("=")) === "authToken";
-    });
-    if (!authCookie) {
-      throw new Error("No authToken cookie found in login response");
-    }
-
-    // Take everything after the FIRST "=" up to the first ";".
-    // Splitting on "=" would truncate base64 values containing "=" padding.
-    const kv = authCookie.split(";")[0];
-    const token = kv.slice(kv.indexOf("=") + 1);
-    return token;
+    return extractAuthTokenFromSetCookie(response.headers["set-cookie"]);
   } catch (error: any) {
     // Avoid leaking the full server response body by default; log only the
     // HTTP status. Log the verbose body only when DEBUG is set.
diff --git a/packages/mcp/test/unit/auth-cookie.test.mjs b/packages/mcp/test/unit/auth-cookie.test.mjs
new file mode 100644
index 00000000..92206cf4
--- /dev/null
+++ b/packages/mcp/test/unit/auth-cookie.test.mjs
@@ -0,0 +1,93 @@
+// Cookie parsing for the login flow.
+//
+// `performLogin` in auth-utils.ts does a real network POST and then extracts the
+// auth token from the response's Set-Cookie header. The cookie-parsing logic was
+// extracted into the pure, exported helper `extractAuthTokenFromSetCookie` so it
+// can be tested without network I/O; `performLogin` now delegates to it, so these
+// tests cover the exact parsing path the login uses.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { extractAuthTokenFromSetCookie } from "../../build/lib/auth-utils.js";
+
+// ---------------------------------------------------------------------------
+// Happy path: a single authToken cookie with attributes.
+// ---------------------------------------------------------------------------
+test("extracts the authToken value, ignoring trailing attributes", () => {
+  const cookies = [
+    "authToken=abc123; Path=/; HttpOnly; Secure; SameSite=Lax",
+  ];
+  assert.equal(extractAuthTokenFromSetCookie(cookies), "abc123");
+});
+
+// ---------------------------------------------------------------------------
+// A base64/JWT value containing "=" padding must NOT be truncated: only the
+// FIRST "=" separates name from value.
+// ---------------------------------------------------------------------------
+test("preserves an '=' inside the value (base64 padding is not truncated)", () => {
+  const jwt = "eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxIn0=";
+  const cookies = [`authToken=${jwt}; Path=/`];
+  assert.equal(extractAuthTokenFromSetCookie(cookies), jwt);
+});
+
+// ---------------------------------------------------------------------------
+// Exact-name match: a different cookie whose name merely STARTS WITH "authToken"
+// (e.g. authTokenRefresh) must not be picked up; the real authToken wins.
+// ---------------------------------------------------------------------------
+test("matches the cookie name exactly, not by prefix (authTokenRefresh ignored)", () => {
+  const cookies = [
+    "authTokenRefresh=refreshvalue; Path=/; HttpOnly",
+    "authToken=realtoken; Path=/; HttpOnly",
+  ];
+  assert.equal(extractAuthTokenFromSetCookie(cookies), "realtoken");
+});
+
+// ---------------------------------------------------------------------------
+// Picks the authToken out of several unrelated cookies regardless of order.
+// ---------------------------------------------------------------------------
+test("selects authToken among multiple unrelated cookies", () => {
+  const cookies = [
+    "session=xyz; Path=/",
+    "authToken=tok-7; Path=/; HttpOnly",
+    "theme=dark",
+  ];
+  assert.equal(extractAuthTokenFromSetCookie(cookies), "tok-7");
+});
+
+// ---------------------------------------------------------------------------
+// An empty value is valid and returns "".
+// ---------------------------------------------------------------------------
+test("returns an empty string when authToken has an empty value", () => {
+  assert.equal(extractAuthTokenFromSetCookie(["authToken=; Path=/"]), "");
+});
+
+// ---------------------------------------------------------------------------
+// Missing Set-Cookie header -> documented error.
+// ---------------------------------------------------------------------------
+test("throws when there is no Set-Cookie header", () => {
+  assert.throws(
+    () => extractAuthTokenFromSetCookie(undefined),
+    /No Set-Cookie header/,
+  );
+});
+
+// ---------------------------------------------------------------------------
+// Set-Cookie present but no authToken cookie -> documented error.
+// ---------------------------------------------------------------------------
+test("throws when no authToken cookie is present", () => {
+  assert.throws(
+    () => extractAuthTokenFromSetCookie(["session=xyz; Path=/", "theme=dark"]),
+    /No authToken cookie/,
+  );
+});
+
+// ---------------------------------------------------------------------------
+// An empty cookie array also yields the "no authToken" error (header exists but
+// is empty), distinct from the "no Set-Cookie header" case above.
+// ---------------------------------------------------------------------------
+test("throws 'no authToken' (not 'no header') for an empty cookie array", () => {
+  assert.throws(
+    () => extractAuthTokenFromSetCookie([]),
+    /No authToken cookie/,
+  );
+});
diff --git a/packages/mcp/test/unit/comment-anchor-apply.test.mjs b/packages/mcp/test/unit/comment-anchor-apply.test.mjs
new file mode 100644
index 00000000..46049c02
--- /dev/null
+++ b/packages/mcp/test/unit/comment-anchor-apply.test.mjs
@@ -0,0 +1,111 @@
+// applyAnchorInDoc — first-match / ambiguity / boundary behavior.
+//
+// comment-anchor.test.mjs already covers the core apply paths (single-node
+// match, spanning adjacent text nodes, code/italic boundary mark preservation,
+// smart-quote normalization, no-match-no-mutation, pre-existing comment mark
+// replacement, nested-list DFS). This file focuses on the SELECTION/RESOLUTION
+// behavior those tests don't pin down: which occurrence/block wins when a
+// selection appears more than once, sub-word ranges, and the run boundary
+// created by a non-text inline node.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { applyAnchorInDoc, canAnchorInDoc } from "../../build/lib/comment-anchor.js";
+
+const commentMark = (node) =>
+  (Array.isArray(node.marks) ? node.marks : []).find((m) => m && m.type === "comment") || null;
+const paragraphDoc = (content) => ({ type: "doc", content: [{ type: "paragraph", content }] });
+
+// ---------------------------------------------------------------------------
+// Document order: when two separate blocks both contain the selection, only the
+// FIRST block (DFS document order) is anchored; the second is left untouched.
+// ---------------------------------------------------------------------------
+test("anchors only the FIRST block when the selection occurs in two blocks", () => {
+  const doc = {
+    type: "doc",
+    content: [
+      { type: "paragraph", content: [{ type: "text", text: "first target here" }] },
+      { type: "paragraph", content: [{ type: "text", text: "second target here" }] },
+    ],
+  };
+  assert.equal(applyAnchorInDoc(doc, "target", "C"), true);
+
+  const marked0 = doc.content[0].content.filter((p) => commentMark(p));
+  const marked1 = doc.content[1].content.filter((p) => commentMark(p));
+  assert.equal(marked0.length, 1, "first block is anchored");
+  assert.equal(marked0[0].text, "target");
+  assert.equal(marked1.length, 0, "second block is left untouched");
+});
+
+// ---------------------------------------------------------------------------
+// Ambiguity within one block: indexOf finds the FIRST occurrence, so only the
+// first "ab" is marked; the later occurrences stay in one unmarked fragment.
+// ---------------------------------------------------------------------------
+test("anchors only the FIRST occurrence within a block (ambiguous selection)", () => {
+  const doc = paragraphDoc([{ type: "text", text: "ab ab ab" }]);
+  assert.equal(applyAnchorInDoc(doc, "ab", "C"), true);
+
+  const parts = doc.content[0].content;
+  assert.equal(parts.length, 2, "split into [marked, rest]");
+  assert.equal(parts[0].text, "ab");
+  assert.ok(commentMark(parts[0]), "first occurrence is marked");
+  assert.equal(parts[1].text, " ab ab");
+  assert.equal(commentMark(parts[1]), null, "later occurrences are not marked");
+});
+
+// ---------------------------------------------------------------------------
+// Sub-word range: a selection that is a substring inside a single text node is
+// spliced into before / marked / after, marking exactly the matched characters.
+// ---------------------------------------------------------------------------
+test("anchors a sub-word range inside a single text node", () => {
+  const doc = paragraphDoc([{ type: "text", text: "Hello" }]);
+  assert.equal(applyAnchorInDoc(doc, "ell", "C"), true);
+
+  const parts = doc.content[0].content;
+  assert.deepEqual(parts.map((p) => p.text), ["H", "ell", "o"]);
+  assert.equal(commentMark(parts[0]), null);
+  assert.ok(commentMark(parts[1]), "only the matched substring is marked");
+  assert.equal(commentMark(parts[2]), null);
+});
+
+// ---------------------------------------------------------------------------
+// A non-text inline node (hardBreak) breaks the matching run: a selection that
+// would span the break cannot match, but one wholly inside a run still does.
+// ---------------------------------------------------------------------------
+test("a non-text inline node breaks the run: cross-break selection does not match", () => {
+  const make = () =>
+    paragraphDoc([
+      { type: "text", text: "foo" },
+      { type: "hardBreak" },
+      { type: "text", text: "bar" },
+    ]);
+
+  // "foobar" straddles the hardBreak -> no match, no mutation.
+  const docA = make();
+  const before = JSON.stringify(docA);
+  assert.equal(canAnchorInDoc(docA, "foobar"), false);
+  assert.equal(applyAnchorInDoc(docA, "foobar", "C"), false);
+  assert.equal(JSON.stringify(docA), before, "failed match must not mutate");
+
+  // "foo" lives entirely in the first run -> matches and is marked; the
+  // hardBreak node is preserved untouched.
+  const docB = make();
+  assert.equal(applyAnchorInDoc(docB, "foo", "C"), true);
+  const parts = docB.content[0].content;
+  assert.equal(parts[0].text, "foo");
+  assert.ok(commentMark(parts[0]));
+  assert.equal(parts[1].type, "hardBreak", "the inline atom is preserved");
+  assert.equal(parts[2].text, "bar");
+  assert.equal(commentMark(parts[2]), null);
+});
+
+// ---------------------------------------------------------------------------
+// A whitespace-only selection normalizes to empty and never anchors.
+// ---------------------------------------------------------------------------
+test("a whitespace-only selection does not anchor and does not mutate", () => {
+  const doc = paragraphDoc([{ type: "text", text: "hello world" }]);
+  const before = JSON.stringify(doc);
+  assert.equal(canAnchorInDoc(doc, "   "), false);
+  assert.equal(applyAnchorInDoc(doc, "   ", "C"), false);
+  assert.equal(JSON.stringify(doc), before);
+});
diff --git a/packages/mcp/test/unit/media-roundtrip-attrs.test.mjs b/packages/mcp/test/unit/media-roundtrip-attrs.test.mjs
new file mode 100644
index 00000000..37668fe0
--- /dev/null
+++ b/packages/mcp/test/unit/media-roundtrip-attrs.test.mjs
@@ -0,0 +1,135 @@
+// Extra media round-trip coverage (issue #244), complementing
+// media-roundtrip.test.mjs.
+//
+// The existing media-roundtrip.test.mjs already asserts that video, youtube,
+// embed, excalidraw, audio and pdf SURVIVE a PM -> markdown -> PM round-trip and
+// keeps their identifying src / provider / name / attachmentId. It does NOT,
+// however, exercise:
+//   * the `drawio` node (a distinct schema node that shares the excalidraw
+//     converter case) — not covered at all;
+//   * the dimension / layout attributes (width, height, align) that ride in
+//     data-* attributes — exactly where a converter<->schema mismatch silently
+//     drops a value while the node itself survives;
+//   * attribute escaping for a src containing `"` (escapeAttr) — a malformed
+//     value here would either break the round-trip or inject HTML.
+//
+// These are the gaps this file locks down.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { convertProseMirrorToMarkdown } from "../../build/lib/markdown-converter.js";
+import { markdownToProseMirror } from "../../build/lib/collaboration.js";
+
+const doc = (...content) => ({ type: "doc", content });
+
+const findAll = (node, type, acc = []) => {
+  if (!node || typeof node !== "object") return acc;
+  if (node.type === type) acc.push(node);
+  for (const c of node.content || []) findAll(c, type, acc);
+  return acc;
+};
+
+// PM node -> markdown -> PM; return both the markdown and the matching nodes.
+const roundtrip = async (node, type) => {
+  const md = convertProseMirrorToMarkdown(doc(node));
+  const pm = await markdownToProseMirror(md);
+  return { md, found: findAll(pm, type) };
+};
+
+// ---------------------------------------------------------------------------
+// drawio: a separate schema node sharing the excalidraw converter case. Not
+// covered by the existing file at all, so guard its full round-trip here.
+// ---------------------------------------------------------------------------
+test("round-trip: drawio diagram survives with src, title, dimensions, align, attachmentId", async () => {
+  const { md, found } = await roundtrip(
+    {
+      type: "drawio",
+      attrs: {
+        src: "/api/files/d.drawio",
+        title: "Flow",
+        width: 400,
+        height: 300,
+        align: "left",
+        attachmentId: "dz1",
+      },
+    },
+    "drawio",
+  );
+  // The converter must emit the schema-matching div[data-type="drawio"].
+  assert.match(md, /data-type="drawio"/);
+  assert.equal(found.length, 1, "drawio node must survive the round-trip");
+  const a = found[0].attrs;
+  assert.equal(a.src, "/api/files/d.drawio");
+  assert.equal(a.title, "Flow");
+  assert.equal(a.attachmentId, "dz1");
+  assert.equal(a.align, "left");
+  // Numeric dimensions come back as strings via the schema parseHTML.
+  assert.equal(String(a.width), "400");
+  assert.equal(String(a.height), "300");
+});
+
+// ---------------------------------------------------------------------------
+// Dimension + align attrs ride in data-* (or width/height) attributes. The
+// existing file checks only src/provider/name/attachmentId, so a dropped
+// width/height/align would pass there but fail here.
+// ---------------------------------------------------------------------------
+test("round-trip: youtube preserves width/height/align (data-* attrs)", async () => {
+  const { found } = await roundtrip(
+    { type: "youtube", attrs: { src: "https://youtube.com/watch?v=x", width: 560, height: 315, align: "left" } },
+    "youtube",
+  );
+  assert.equal(found.length, 1);
+  const a = found[0].attrs;
+  assert.equal(String(a.width), "560");
+  assert.equal(String(a.height), "315");
+  assert.equal(a.align, "left");
+});
+
+test("round-trip: embed preserves provider, width/height and align", async () => {
+  const { found } = await roundtrip(
+    { type: "embed", attrs: { src: "https://e.com/x", provider: "iframe", width: 600, height: 480, align: "right" } },
+    "embed",
+  );
+  assert.equal(found.length, 1);
+  const a = found[0].attrs;
+  assert.equal(a.provider, "iframe");
+  assert.equal(String(a.width), "600");
+  assert.equal(String(a.height), "480");
+  assert.equal(a.align, "right");
+});
+
+test("round-trip: video preserves width/height and align (data-align)", async () => {
+  const { found } = await roundtrip(
+    { type: "video", attrs: { src: "/api/files/v.mp4", attachmentId: "att1", width: 640, height: 360, align: "right" } },
+    "video",
+  );
+  assert.equal(found.length, 1);
+  const a = found[0].attrs;
+  assert.equal(String(a.width), "640");
+  assert.equal(String(a.height), "360");
+  assert.equal(a.align, "right");
+});
+
+test("round-trip: pdf preserves width/height (standard attrs) plus name", async () => {
+  const { found } = await roundtrip(
+    { type: "pdf", attrs: { src: "/api/files/x.pdf", name: "x.pdf", attachmentId: "a4", width: 700, height: 900 } },
+    "pdf",
+  );
+  assert.equal(found.length, 1);
+  const a = found[0].attrs;
+  assert.equal(a.name, "x.pdf");
+  assert.equal(String(a.width), "700");
+  assert.equal(String(a.height), "900");
+});
+
+// ---------------------------------------------------------------------------
+// Escaping: a src containing a double quote must survive the attribute-quoted
+// HTML emission (escapeAttr) and re-parse to the exact original value, with no
+// node loss and no HTML injection.
+// ---------------------------------------------------------------------------
+test("round-trip: a src containing a double quote is escaped and recovered intact", async () => {
+  const tricky = 'https://e.com/x?a="b"&c=1';
+  const { found } = await roundtrip({ type: "youtube", attrs: { src: tricky } }, "youtube");
+  assert.equal(found.length, 1, "node must survive a quote-bearing src");
+  assert.equal(found[0].attrs.src, tricky, "the exact src is recovered");
+});
diff --git a/packages/mcp/test/unit/recreate-transform-drift.test.mjs b/packages/mcp/test/unit/recreate-transform-drift.test.mjs
new file mode 100644
index 00000000..b950cdaf
--- /dev/null
+++ b/packages/mcp/test/unit/recreate-transform-drift.test.mjs
@@ -0,0 +1,139 @@
+// CONTRACT / DRIFT GUARD: mcp diff vs the vendored editor-ext recreate-transform.
+//
+// packages/mcp/src/lib/diff.ts computes its document diff with
+// `recreateTransform` from the published @fellow/prosemirror-recreate-transform
+// package. Docmost's in-app history editor computes the SAME diff with its own
+// vendored copy at
+// packages/editor-ext/src/lib/recreate-transform/recreateTransform.ts.
+// diff.ts's header comment claims the two are "identical" — if they ever drift,
+// the headless mcp diff would stop matching what a user sees in the app.
+//
+// This test guards that claim two ways, on representative doc pairs, using the
+// EXACT options diff.ts passes (complexSteps:false, wordDiffs:true,
+// simplifyDiff:true):
+//   1. invariant: each implementation's transform reproduces the target doc
+//      (apply(diff) == target);
+//   2. cross-copy parity: both implementations emit the SAME step sequence, so a
+//      behavioral divergence between the two copies fails this test.
+//
+// The vendored copy is TypeScript, so it is transpiled to CommonJS at test time
+// and required directly — the test runs the ACTUAL vendored source, not a stand-in.
+import { test, before } from "node:test";
+import assert from "node:assert/strict";
+import ts from "typescript";
+import fs from "node:fs";
+import path from "node:path";
+import { createRequire } from "node:module";
+import { fileURLToPath } from "node:url";
+
+import { recreateTransform as fellowRecreate } from "@fellow/prosemirror-recreate-transform";
+import { Node } from "@tiptap/pm/model";
+import { docmostSchema } from "../../build/lib/docmost-schema.js";
+
+const require = createRequire(import.meta.url);
+const HERE = path.dirname(fileURLToPath(import.meta.url));
+// .../packages/mcp/test/unit -> repo packages root.
+const PACKAGES = path.resolve(HERE, "..", "..", "..");
+const VENDOR_SRC = path.join(
+  PACKAGES,
+  "editor-ext",
+  "src",
+  "lib",
+  "recreate-transform",
+);
+// Emit transpiled CJS under mcp/build so Node resolves the hoisted deps
+// (@tiptap/pm, rfc6902, diff) up the directory tree exactly as diff.js does.
+const VENDOR_OUT = path.resolve(HERE, "..", "..", "build", "_vendored_editor_ext");
+
+// The exact options the mcp diff pipeline uses (diff.ts).
+const DIFF_OPTS = { complexSteps: false, wordDiffs: true, simplifyDiff: true };
+
+let vendoredRecreate;
+
+before(() => {
+  assert.ok(
+    fs.existsSync(VENDOR_SRC),
+    `vendored recreate-transform sources missing at ${VENDOR_SRC}`,
+  );
+  fs.rmSync(VENDOR_OUT, { recursive: true, force: true });
+  fs.mkdirSync(VENDOR_OUT, { recursive: true });
+  // Mark the output as CommonJS so relative `require("./x")` resolves to x.js.
+  fs.writeFileSync(
+    path.join(VENDOR_OUT, "package.json"),
+    JSON.stringify({ type: "commonjs" }),
+  );
+  for (const f of fs.readdirSync(VENDOR_SRC)) {
+    if (!f.endsWith(".ts")) continue;
+    const code = fs.readFileSync(path.join(VENDOR_SRC, f), "utf8");
+    const out = ts.transpileModule(code, {
+      compilerOptions: {
+        module: ts.ModuleKind.CommonJS,
+        target: ts.ScriptTarget.ES2020,
+      },
+    });
+    fs.writeFileSync(path.join(VENDOR_OUT, f.replace(/\.ts$/, ".js")), out.outputText);
+  }
+  vendoredRecreate = require(path.join(VENDOR_OUT, "index.js")).recreateTransform;
+  assert.equal(typeof vendoredRecreate, "function", "vendored recreateTransform loaded");
+});
+
+// ---------------------------------------------------------------------------
+// Builders + representative doc pairs covering the diff shapes diff.ts handles.
+// ---------------------------------------------------------------------------
+const t = (text, marks) => (marks ? { type: "text", text, marks } : { type: "text", text });
+const para = (...c) => ({ type: "paragraph", content: c });
+const doc = (...c) => ({ type: "doc", content: c });
+
+const PAIRS = [
+  // word inserted mid-sentence
+  ["insert word", doc(para(t("Hello world"))), doc(para(t("Hello brave world")))],
+  // whole block deleted
+  ["delete block", doc(para(t("keep this")), para(t("remove this"))), doc(para(t("keep this")))],
+  // word removed mid-sentence
+  ["delete word", doc(para(t("one two three"))), doc(para(t("one three")))],
+  // pure mark addition (complexSteps:false treats it as a content step)
+  ["add mark", doc(para(t("plain"))), doc(para(t("plain", [{ type: "bold" }])))],
+  // two blocks swapped (reorder)
+  ["reorder blocks", doc(para(t("a")), para(t("b"))), doc(para(t("b")), para(t("a")))],
+  // structural insert: an image node appears
+  [
+    "insert image",
+    doc(para(t("caption"))),
+    doc(para(t("caption")), { type: "image", attrs: { src: "/api/files/a.png", attachmentId: "i1" } }),
+  ],
+];
+
+const stepsJSON = (tr) => JSON.stringify(tr.steps.map((s) => s.toJSON()));
+
+for (const [label, fromJSON, toJSON] of PAIRS) {
+  test(`invariant: @fellow recreateTransform reproduces the target (${label})`, () => {
+    const from = Node.fromJSON(docmostSchema, fromJSON);
+    const to = Node.fromJSON(docmostSchema, toJSON);
+    const tr = fellowRecreate(from, to, DIFF_OPTS);
+    // apply(diff) == target, comparing schema-normalized JSON on both sides.
+    assert.equal(JSON.stringify(tr.doc.toJSON()), JSON.stringify(to.toJSON()));
+  });
+
+  test(`drift: @fellow and vendored editor-ext emit identical steps (${label})`, () => {
+    const mk = () => [
+      Node.fromJSON(docmostSchema, fromJSON),
+      Node.fromJSON(docmostSchema, toJSON),
+    ];
+    const [fA, tA] = mk();
+    const [fB, tB] = mk();
+    const trFellow = fellowRecreate(fA, tA, DIFF_OPTS);
+    const trVendor = vendoredRecreate(fB, tB, DIFF_OPTS);
+
+    // Both must reach the same target...
+    const target = JSON.stringify(tA.toJSON());
+    assert.equal(JSON.stringify(trFellow.doc.toJSON()), target, "fellow reaches target");
+    assert.equal(JSON.stringify(trVendor.doc.toJSON()), target, "vendored reaches target");
+    // ...and, critically, via the SAME step sequence. A divergence in the two
+    // recreate-transform copies' algorithm would change the steps and fail here.
+    assert.equal(
+      stepsJSON(trVendor),
+      stepsJSON(trFellow),
+      `vendored editor-ext drifted from @fellow on "${label}"`,
+    );
+  });
+}