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>

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);