test(coverage): add regression tests for issues #192, #206, #204

Additive test coverage across server, editor-ext, client and mcp.

#192 — AiChatService.stream integration (Section 3, against real Postgres):
- new apps/server/test/integration/ai-chat-stream.int-spec.ts drives the real
  streamText through a seeded ai/test MockLanguageModelV3 and a real Node
  ServerResponse, covering: onError persists an assistant error record
  (status 'error' + partial answer + provider cause in metadata); external MCP
  client closed exactly once on BOTH onFinish and onError; anti-tamper —
  history is rebuilt from the DB transcript, not from body.messages.

#206 — red-team findings (most already fixed+tested in #212):
- mdrt-2 (UNFIXED, data loss): turndown.dataloss.test.ts documents that
  pageBreak / transclusionReference / mention are silently dropped on Markdown
  export (characterization + it.fails for the desired survive-export contract).
- persist-6 (UNFIXED, data loss): persistence-store.spec.ts adds an it.failing
  documenting that a momentarily-empty live doc overwrites non-empty content
  (left unfixed — a store-side empty-guard is a behaviour change).

#204 — test-strategy plan, highest-priority subset:
- Phase 1: mcp-clients.lease.spec.ts covers the external MCP client
  lease/refcount/eviction lifecycle (leak / premature-close / double-close).
- Phase 2 data-integrity pure functions: editor-ext table-utils
  (transpose/moveRow/convert round-trip) and math tokenizer false-positive
  guard; client emoji-menu (+ it.fails for the unguarded localStorage
  JSON.parse bug), sort-cells, normalizeTableColumnWidths; mcp htmlEmbed/
  pageBreak markdown data-loss + footnote-diff; server export
  getInternalLinkPageName extensionless-path bug — FIXED (small/clear) + tested.

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

packages/mcp/test/unit/footnote-diff.test.mjs

@@ -0,0 +1,86 @@
+// Footnote-marker extraction in the integrity diff (diff.ts `footnoteMarkers`,
+// surfaced via diffDocs(...).integrity.footnoteMarkers).
+//
+// The existing diff.test.mjs covers the basic legacy `[N]` body markers and the
+// default notes-heading split. These add the cases it does not:
+//  - real footnoteReference nodes take precedence over legacy `[N]` text,
+//  - the notesHeading parameter is configurable,
+//  - footnoteReference nodes are numbered 1..n by reading position.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { diffDocs } from "../../build/lib/diff.js";
+
+// Builders.
+const doc = (...content) => ({ type: "doc", content });
+const para = (...content) => ({ type: "paragraph", content });
+const t = (text) => ({ type: "text", text });
+const heading = (level, text) => ({ type: "heading", attrs: { level }, content: [t(text)] });
+const fref = () => ({ type: "footnoteReference" });
+
+// ---------------------------------------------------------------------------
+// footnoteReference nodes take precedence over legacy [N] text markers.
+// ---------------------------------------------------------------------------
+test("footnoteReference nodes are numbered 1..n by reading position", () => {
+  const d = doc(para(t("a"), fref(), t(" b "), fref(), t(" c "), fref()));
+  const r = diffDocs(d, d);
+  // Three refs -> [1, 2, 3] regardless of any stored number.
+  assert.deepEqual(r.integrity.footnoteMarkers, [[1, 2, 3], [1, 2, 3]]);
+});
+
+test("when real footnoteReference nodes exist, legacy [N] text markers are ignored", () => {
+  // Body has TWO footnoteReference nodes AND a literal "[9]" text marker.
+  // The refs win: the literal [9] must NOT contribute a marker.
+  const d = doc(para(t("intro "), fref(), t(" middle [9] tail "), fref()));
+  const r = diffDocs(d, d);
+  assert.deepEqual(
+    r.integrity.footnoteMarkers,
+    [[1, 2], [1, 2]],
+    "literal [9] is dropped when footnoteReference nodes are present",
+  );
+});
+
+// ---------------------------------------------------------------------------
+// The notesHeading split is configurable; the body/notes boundary follows it.
+// ---------------------------------------------------------------------------
+test("a custom notesHeading splits body from notes for legacy markers", () => {
+  const d = doc(
+    para(t("body [1] [2]")),
+    heading(2, "Notes"),
+    para(t("note text [1] inside notes")),
+  );
+  // With notesHeading="Notes" only the body markers [1],[2] are counted; the
+  // [1] under the heading is excluded.
+  const r = diffDocs(d, d, "Notes");
+  assert.deepEqual(r.integrity.footnoteMarkers, [[1, 2], [1, 2]]);
+});
+
+test("a notesHeading that does not match any heading counts the whole doc", () => {
+  const d = doc(
+    para(t("body [1] [2]")),
+    heading(2, "Notes"),
+    para(t("note text [1] inside notes")),
+  );
+  // The default heading ("Примечания переводчика") does not match "Notes", so
+  // there is no body/notes split and ALL three markers are counted in order.
+  const r = diffDocs(d, d);
+  assert.deepEqual(r.integrity.footnoteMarkers, [[1, 2, 1], [1, 2, 1]]);
+});
+
+// ---------------------------------------------------------------------------
+// Legacy markers preserve their literal value and reading order; the diff
+// surfaces added/removed markers between two docs.
+// ---------------------------------------------------------------------------
+test("legacy [N] markers keep their literal numbers in reading order", () => {
+  // Out-of-sequence literal numbers must be preserved verbatim (not renumbered).
+  const d = doc(para(t("see [3] then [1] then [10]")));
+  const r = diffDocs(d, d);
+  assert.deepEqual(r.integrity.footnoteMarkers, [[3, 1, 10], [3, 1, 10]]);
+});
+
+test("a dropped legacy marker shows up as an [old,new] difference", () => {
+  const oldDoc = doc(para(t("a [1] b [2] c [3]")));
+  const newDoc = doc(para(t("a [1] b [3]")));
+  const r = diffDocs(oldDoc, newDoc);
+  assert.deepEqual(r.integrity.footnoteMarkers, [[1, 2, 3], [1, 3]]);
+});