feat(f11): SLICE-3 — Edit Document button + per-hunk proposal path (#43, INV-37)

A whole-document Ask-Claude rewrite is diffed into hunks and surfaced as N
independent F4 proposals (one per changed hunk) — reusing the F4 single-range
model N times, no new model. Per spec §6.4/§7.2 SLICE-3.

- trackChangesModel: pure `diffToHunks(currentText, rewrittenText)` →
  EditHunk[] (vscode-free, deterministic; diffWordsWithSpace, coalescing
  adjacent add/remove runs; offsets index currentText).
- trackChangesPreview: `runEditAndPropose(document, target, instruction)` — the
  shared host routine (selection → one single-range propose; document → diff →
  one propose per hunk; never mutates the doc, INV-10); `askClaude` UI wrapper
  (host showInputBox keeps LLM/secrets out of the sealed webview, INV-8/35);
  injectable `editTurn` + `setEditTurnForTest` seam (no LLM in CI); the
  `askClaude` inbound message branch; `cowriting.editDocument` command for #42
  reuse.
- package.json: register cowriting.editDocument, palette-guarded on markdown.
- webview: ✦ Ask Claude to Edit Document button → { askClaude, scope:"document" }.
- unit: diffToHunks fixtures (zero/one/multi-hunk, wholesale, determinism).
- host E2E: stubbed multi-hunk rewrite → N matching proposals, doc untouched;
  editDocument command registered + markdown-guarded.

205 unit + 49 host E2E green.

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

test/e2e/suite/f11Toolbar.test.ts

@@ -66,4 +66,50 @@ suite("F11 preview toolbar (host E2E — message → seam wiring, no LLM)", () =
     assert.notStrictEqual(entry!.when, "false", "it is no longer hidden (when:false)");
     assert.match(entry!.when ?? "", /editorLangId == markdown/, "guarded on markdown");
   });
+
+  // SLICE-3: Edit Document → a whole-document rewrite diffed into N F4 proposals.
+  test("runEditAndPropose(document) with a stubbed multi-hunk rewrite → N proposals matching the hunks (PUC-4, INV-37)", async () => {
+    const { doc, key } = await freshDoc(
+      "docs/f11doc.md",
+      "# F11 doc\n\nThe quick brown fox jumps over the lazy dog.\n",
+    );
+    const api = await getApi();
+    const ctl = api.trackChangesPreviewController;
+    await vscode.commands.executeCommand("cowriting.showTrackChangesPreview");
+    await settle();
+
+    // Stub the host edit turn (no LLM in CI): rewrite two distinct words.
+    ctl.setEditTurnForTest(async () => ({
+      replacement: "# F11 doc\n\nThe quick RED fox jumps over the lazy CAT.\n",
+      model: "sonnet",
+      sessionId: "e2e-f11-doc",
+    }));
+
+    const ids = await ctl.runEditAndPropose(doc, { kind: "document" }, "swap brown→RED and dog→CAT");
+    await settle();
+    assert.strictEqual(ids.length, 2, "two changed words → two independent proposals");
+
+    const views = api.proposalController.listProposals(doc);
+    assert.ok(
+      ids.every((id) => views.some((v) => v.id === id)),
+      "every returned proposal id is a live pending proposal",
+    );
+    const replacements = views.map((v) => v.replacement);
+    assert.ok(replacements.includes("RED") && replacements.includes("CAT"), "proposals carry the per-hunk replacements");
+    // INV-10: proposing never mutates the document.
+    assert.ok(doc.getText().includes("brown fox") && doc.getText().includes("lazy dog"), "document unchanged by propose");
+    void key;
+  });
+
+  // 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);
+    assert.ok(all.includes("cowriting.editDocument"), "editDocument command registered");
+    const pkg = JSON.parse(fs.readFileSync(path.join(__dirname, "../../../../package.json"), "utf8"));
+    const entry = (pkg.contributes.menus.commandPalette as Array<{ command: string; when?: string }>).find(
+      (m) => m.command === "cowriting.editDocument",
+    );
+    assert.ok(entry, "editDocument has a commandPalette entry");
+    assert.match(entry!.when ?? "", /editorLangId == markdown/, "guarded on markdown");
+  });
 });