fix(f11): address code review — insertion anchoring, turnId, accept-all coverage (#43)

Code-review follow-up on the F11 branch (5966907..1564ef5). Three real findings:

- CRITICAL — pure-insertion hunks were born-orphaned. A document rewrite that
  INSERTS text produced a zero-width hunk (start==end) → buildFingerprint yields
  empty fp.text → anchorer.resolve orphans an empty needle → the proposal could
  never be accepted (silently). diffToHunks now anchors every zero-width
  insertion to an adjacent source token (anchorInsertion): the range absorbs the
  token and the replacement keeps it, so net text is identical but fp.text is
  non-empty and resolvable. New unit tests: applying hunks always reconstructs
  the rewrite (substitute/delete/insert/multi); insertions are never zero-width.
  New host E2E ACCEPTS a rewrite-with-insertion end to end and asserts accept-all
  reconstructs the intended document (also covers sequential multi-hunk accept).

- IMPORTANT — renderPlain cross-block fidelity. The per-block off-mode rendering
  (SLICE-2) can't resolve a reference-link definition in a separate block.
  Documented as a conscious tradeoff of the operator-locked block-level mapping
  (§6.7) — renderReview already rendered per-block, so this keeps both modes
  consistent — with a characterization test + a docstring note.

- MINOR — F11 proposals now carry a turnId (one per Ask-Claude gesture, shared
  across a document rewrite's N hunks), matching the editor-menu editSelection
  path so a rewrite groups as one agent turn.

208 unit + 9/9 F11 host E2E green. (The lone red E2E is a pre-existing,
F11-independent undoMarks timing flake — proven by isolation: it fails
identically with all F11 tests removed.)

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

src/trackChangesModel.ts

@@ -211,13 +211,23 @@ export interface EditHunk {
  * unchanged parts reconstruct it exactly, so advancing on those yields true
  * source offsets. Adjacent added/removed runs coalesce into one hunk; an
  * unchanged part flushes the open hunk.
+ *
+ * A PURE insertion (added text between two unchanged regions) would otherwise be
+ * a zero-width hunk (start==end) — and F4's fingerprint of empty text can never
+ * resolve (anchorer.resolve orphans an empty needle), so the proposal could
+ * never be accepted. Every zero-width hunk is therefore anchored to an adjacent
+ * source token (`anchorInsertion`): its range absorbs that token and its
+ * replacement keeps it, so the net text is identical but `fp.text` is non-empty
+ * and resolvable. A zero-width hunk is always bordered by unchanged text (or a
+ * doc edge), so the absorbed token is genuinely present in `currentText` and is
+ * never part of another hunk.
  */
 export function diffToHunks(currentText: string, rewrittenText: string): EditHunk[] {
   const hunks: EditHunk[] = [];
   let offset = 0;
   let open: EditHunk | null = null;
   const flush = () => {
-    if (open) hunks.push(open);
+    if (open) hunks.push(open.start === open.end ? anchorInsertion(open, currentText) : open);
     open = null;
   };
   for (const part of diffWordsWithSpace(currentText, rewrittenText)) {
@@ -237,6 +247,31 @@ export function diffToHunks(currentText: string, rewrittenText: string): EditHun
   return hunks;
 }
 
+const isWs = (c: string): boolean => /\s/.test(c);
+
+/**
+ * Grow a zero-width insertion hunk to absorb an adjacent source token so its F4
+ * fingerprint has real text to resolve. Prefer the FOLLOWING token (optional
+ * leading whitespace + a run of non-whitespace); at end-of-document, fall back to
+ * the PRECEDING token. The absorbed text is kept in the replacement, so the
+ * applied result is unchanged.
+ */
+function anchorInsertion(hunk: EditHunk, text: string): EditHunk {
+  const p = hunk.start;
+  if (p < text.length) {
+    let e = p;
+    while (e < text.length && isWs(text[e])) e++;
+    while (e < text.length && !isWs(text[e])) e++;
+    if (e === p) e = Math.min(text.length, p + 1);
+    return { start: p, end: e, replacement: hunk.replacement + text.slice(p, e) };
+  }
+  let s = p;
+  while (s > 0 && isWs(text[s - 1])) s--;
+  while (s > 0 && !isWs(text[s - 1])) s--;
+  if (s === p) s = Math.max(0, p - 1);
+  return { start: s, end: p, replacement: text.slice(s, p) + hunk.replacement };
+}
+
 const md = new MarkdownIt({ html: true, linkify: false, breaks: false });
 // mermaid fences → <pre class="mermaid">SRC</pre> for client-side rendering; all
 // other fences fall through to markdown-it's default (escaped <pre><code>).
@@ -427,6 +462,12 @@ export function colorByAuthor(
  * preview is still a selection→source mapping surface (INV-36) while staying
  * visually clean — no `cw-` annotation classes. A doc with no blocks (empty /
  * whitespace-only) renders whole. Pure + deterministic.
+ *
+ * Tradeoff of the locked block-level mapping (§6.7): rendering PER BLOCK (so each
+ * carries its offsets) means a markdown construct split across blank-line-
+ * separated blocks — a reference-link use and its definition — doesn't resolve
+ * across blocks. `renderReview` already rendered per-block; this keeps the two
+ * modes consistent rather than faithful-but-different. Characterized in tests.
  */
 export function renderPlain(currentText: string, opts: RenderOptions = {}): string {
   const render = opts.render ?? defaultRender;

src/trackChangesPreview.ts

@@ -56,6 +56,11 @@ export class TrackChangesPreviewController implements vscode.Disposable {
     const { runEditTurn } = await import("./liveTurn");
     return runEditTurn(instruction, text);
   };
+  /** Monotonic per-session counter minting a stable turnId for each Ask-Claude gesture. */
+  private turnSeq = 0;
+  private nextTurnSeq(): number {
+    return ++this.turnSeq;
+  }
 
   constructor(
     private readonly diffView: DiffViewController,
@@ -219,6 +224,9 @@ export class TrackChangesPreviewController implements vscode.Disposable {
     instruction: string,
   ): Promise<string[]> {
     const full = document.getText();
+    // One turnId per gesture — the document case's N hunk-proposals all share it,
+    // so a single rewrite groups as one agent turn (parity with editSelection).
+    const turnId = `turn-${this.nextTurnSeq()}`;
     const provenance = (turn: EditTurnResult) =>
       ({ kind: "agent" as const, id: "claude", agent: { sdk: "@cline/sdk", model: turn.model, sessionId: turn.sessionId } });
     if (target.kind === "range") {
@@ -226,14 +234,14 @@ export class TrackChangesPreviewController implements vscode.Disposable {
       const turn = await this.editTurn(instruction, selected);
       if (turn.replacement === "" || turn.replacement === selected) return [];
       const fp = buildFingerprint(full, { start: target.start, end: target.end });
-      const id = await this.proposals.propose(document, fp, turn.replacement, provenance(turn), { instruction });
+      const id = await this.proposals.propose(document, fp, turn.replacement, provenance(turn), { turnId, instruction });
       return id ? [id] : [];
     }
     const turn = await this.editTurn(instruction, full);
     const ids: string[] = [];
     for (const h of diffToHunks(full, turn.replacement)) {
       const fp = buildFingerprint(full, { start: h.start, end: h.end });
-      const id = await this.proposals.propose(document, fp, h.replacement, provenance(turn), { instruction });
+      const id = await this.proposals.propose(document, fp, h.replacement, provenance(turn), { turnId, instruction });
       if (id) ids.push(id);
     }
     return ids;

test/e2e/suite/f11Toolbar.test.ts

@@ -144,6 +144,33 @@ suite("F11 preview toolbar (host E2E — message → seam wiring, no LLM)", () =
     assert.strictEqual(ids.length, 0, "an unchanged replacement proposes nothing");
   });
 
+  // SLICE-3 (review follow-up): a document rewrite that INSERTS text → an
+  // acceptable proposal (not a born-orphaned zero-width hunk), and accepting all
+  // hunks of a multi-hunk rewrite lands the intended document.
+  test("document rewrite with an insertion → acceptable proposals; accept-all reaches the rewrite", async () => {
+    const original = "# F11 accept\n\nThe brown fox sleeps.\n";
+    const rewrite = "# F11 accept\n\nThe brown fox QUIETLY sleeps today.\n";
+    const { doc } = await freshDoc("docs/f11accept.md", original);
+    const api = await getApi();
+    const ctl = api.trackChangesPreviewController;
+    await vscode.commands.executeCommand("cowriting.showTrackChangesPreview");
+    await settle();
+
+    ctl.setEditTurnForTest(async () => ({ replacement: rewrite, model: "sonnet", sessionId: "e2e-accept" }));
+    const ids = await ctl.runEditAndPropose(doc, { kind: "document" }, "expand the sentence");
+    await settle();
+    assert.ok(ids.length >= 1, "the rewrite produced at least one proposal");
+
+    // Every proposal must be acceptable (the insertion-anchoring fix): accept each.
+    for (const id of ids) {
+      const ok = await api.proposalController.acceptById("docs/f11accept.md", id);
+      assert.ok(ok, `proposal ${id} is acceptable (not born-orphaned)`);
+      await settle();
+    }
+    assert.strictEqual(doc.getText(), rewrite, "accepting all hunks reconstructs the intended rewrite");
+    assert.strictEqual(api.proposalController.listProposals(doc).length, 0, "no proposals left pending");
+  });
+
   // SLICE-3: the document-scoped command exists for #42 reuse, guarded on markdown.
   test("cowriting.editDocument is a registered command, palette-guarded on markdown", async () => {
     const all = await vscode.commands.getCommands(true);

test/trackChangesModel.test.ts

@@ -360,6 +360,46 @@ describe("F11 diffToHunks (INV-37)", () => {
     const b = diffToHunks("a b c d", "a B c D");
     expect(a).toEqual(b);
   });
+
+  /** Apply hunks (right→left so earlier offsets stay valid) to reconstruct the rewrite. */
+  const applyHunks = (current: string, hunks: ReturnType<typeof diffToHunks>): string => {
+    let out = current;
+    for (const h of [...hunks].sort((a, b) => b.start - a.start)) {
+      out = out.slice(0, h.start) + h.replacement + out.slice(h.end);
+    }
+    return out;
+  };
+
+  test("applying the hunks always reconstructs the rewrite (substitute / delete / insert / multi)", () => {
+    const cases: Array<[string, string]> = [
+      ["The quick brown fox.", "The quick red fox."],
+      ["one two three four", "one TWO three FOUR"],
+      ["alpha", "omega"],
+      ["keep this and drop that", "keep this"],
+      ["one two three", "one INSERTED two three"],
+      ["start middle end", "PREFIX start middle end SUFFIX"],
+      ["unchanged body", "unchanged body"],
+    ];
+    for (const [current, rewrite] of cases) {
+      expect(applyHunks(current, diffToHunks(current, rewrite))).toBe(rewrite);
+    }
+  });
+
+  test("an inserted run anchors to adjacent text — never a zero-width, unacceptable hunk (INV-37)", () => {
+    // A pure insertion would otherwise produce start==end → an empty fingerprint
+    // → resolve() orphans it → the proposal can never be accepted. Each hunk must
+    // span real source text so its F4 fingerprint resolves.
+    for (const [current, rewrite] of [
+      ["one two three", "one INSERTED two three"],
+      ["tail anchor", "tail anchor APPENDED"],
+      ["lead", "PREPENDED lead"],
+    ] as Array<[string, string]>) {
+      for (const h of diffToHunks(current, rewrite)) {
+        expect(h.end).toBeGreaterThan(h.start); // non-zero-width
+        expect(current.slice(h.start, h.end).length).toBeGreaterThan(0); // real fp.text
+      }
+    }
+  });
 });
 
 // F11 SLICE-2 (INV-36): the pure render layer emits data-src-start/data-src-end
@@ -408,4 +448,23 @@ describe("F11 data-src emission (INV-36)", () => {
     const r2 = renderReview("x", "x\n\ny", [], []);
     expect(r1).toBe(r2);
   });
+
+  // CHARACTERIZATION (conscious tradeoff of the locked block-level mapping, §6.7
+  // fork 1): both modes render markdown PER BLOCK so each block can carry its
+  // data-src offsets. A consequence is that markdown constructs whose parts span
+  // blank-line-separated blocks — a reference-link USE and its DEFINITION — do not
+  // resolve across blocks (markdown-it sees each block in isolation). renderReview
+  // already had this; F11 brings the off/clean preview into line with it (both
+  // per-block) rather than leaving the two modes rendering differently. If
+  // cross-block fidelity is wanted later, it is a follow-up (source-map driven
+  // wrapping), not a change to the locked block-level decision.
+  test("a reference-link definition in a separate block does not resolve (block-level rendering)", () => {
+    const doc = "See [the spec][ref] for details.\n\n[ref]: https://example.com/spec\n";
+    const html = renderPlain(doc);
+    // the link is NOT resolved to an <a href> — the [text][ref] is rendered literally.
+    expect(html).not.toContain('href="https://example.com/spec"');
+    expect(html).toContain("[the spec][ref]");
+    // both modes agree (renderReview is likewise per-block) — the consistency point.
+    expect(renderReview(doc, doc, [], [])).not.toContain('href="https://example.com/spec"');
+  });
 });