feat!: sunset the review-panel webview — built-in preview + native diff are the review surfaces (D3/D17, spec §6.10); Keep/Reject lens copy (PUC-2)

Deletes the last bespoke UI surface (TrackChangesPreviewController + its
sealed webview client assets); every entry point re-points at native VS
Code chrome per spec §5: the #41 right-click entries become
cowriting.openReviewPreview (enter coediting if needed -> "Open Preview to
the Side"), Ctrl+Alt+R/Cmd+Alt+R moves to cowriting.reviewChanges (native
diff), and the F12 CodeLens per-proposal titles read "Keep"/"Reject" with
a top-of-file "Keep all (N)"/"Reject all" pair once >=2 proposals are
pending. EditFlow drops its own askClaude/askEditInstruction (the
webview's only caller) and its now-unused constructor params.

Coverage that lived only in the webview's test seams (renderHtmlFor,
receiveMessage, isOpen, ...) moves to direct calls against the surviving
controllers/pure renderReview (test/e2e/suite/helpers.ts gains a shared
renderHtmlFor probe); a genuine gap (pending-proposal + unchanged-block
rendering) is backfilled in test/previewAnnotations.test.ts. README's "how
it works" is rewritten as the native-surface map; the superseded F6/F7/F9/
F10/F11 sections are kept as a marked historical record rather than
deleted outright.

292 unit + 91 E2E green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/e2e/suite/f12Review.test.ts

@@ -10,7 +10,7 @@ const settle = () => new Promise((r) => setTimeout(r, 400));
 async function getApi(): Promise<CowritingApi> {
   const ext = vscode.extensions.getExtension("benstull.vscode-cowriting-plugin")!;
   const api = (await ext.activate()) as CowritingApi;
-  assert.ok(api?.trackChangesPreviewController && api?.proposalController, "exports controllers");
+  assert.ok(api?.proposalController && api?.editorProposalController, "exports controllers");
   return api;
 }
 
@@ -135,3 +135,55 @@ suite("F12 SLICE-2 — block-granularity document proposals (#47, INV-39/40/41)"
     assert.strictEqual(api.proposalController.listProposals(doc).length, 0, "no proposals left pending");
   });
 });
+
+// Task 8 (PUC-2 lens copy): the CodeLens titles read "✓ Keep"/"✗ Reject" per
+// proposal, and — once ≥2 proposals are pending — a top-of-file "Keep all
+// (N)"/"Reject all" pair routes straight at the batch commands.
+suite("F12 CodeLens copy (Task 8, PUC-2)", () => {
+  test("one pending proposal → a per-proposal ✓ Keep / ✗ Reject pair, no top-of-file pair", async () => {
+    const doc = await freshDoc("docs/f12-lens-one.md", "# Lens\n\nAlpha block here.\n");
+    const api = await getApi();
+    const editFlow = api.editFlow;
+    editFlow.setEditTurnForTest(async () => ({
+      replacement: "# Lens\n\nALPHA block here.\n",
+      model: "sonnet",
+      sessionId: "e2e-lens-one",
+    }));
+    const ids = await editFlow.runEditAndPropose(doc, { kind: "document" }, "uppercase");
+    await settle();
+    assert.strictEqual(ids.length, 1, "one changed block → one proposal");
+
+    const lenses = api.editorProposalController.provideCodeLenses(doc);
+    const titles = lenses.map((l) => l.command?.title);
+    assert.deepStrictEqual(titles, ["✓ Keep", "✗ Reject"], "exactly one per-proposal pair, no top-of-file pair below threshold");
+  });
+
+  test("two pending proposals → a top-of-file 'Keep all (2)'/'Reject all' pair routed at the batch commands", async () => {
+    const doc = await freshDoc(
+      "docs/f12-lens-two.md",
+      "# Lens\n\nFirst block here.\n\nSecond block here.\n",
+    );
+    const api = await getApi();
+    const editFlow = api.editFlow;
+    editFlow.setEditTurnForTest(async () => ({
+      replacement: "# Lens\n\nFIRST block here.\n\nSECOND block here.\n",
+      model: "sonnet",
+      sessionId: "e2e-lens-two",
+    }));
+    const ids = await editFlow.runEditAndPropose(doc, { kind: "document" }, "uppercase both");
+    await settle();
+    assert.strictEqual(ids.length, 2, "two changed blocks → two proposals");
+
+    const lenses = api.editorProposalController.provideCodeLenses(doc);
+    const titles = lenses.map((l) => l.command?.title);
+    assert.strictEqual(titles[0], "✓ Keep all (2)", "top-of-file accept-all lens leads");
+    assert.strictEqual(titles[1], "✗ Reject all", "top-of-file reject-all lens follows");
+    assert.deepStrictEqual(titles.slice(2), ["✓ Keep", "✗ Reject", "✓ Keep", "✗ Reject"], "per-proposal pairs follow");
+
+    const acceptAll = lenses[0].command!;
+    const rejectAll = lenses[1].command!;
+    assert.strictEqual(acceptAll.command, "cowriting.acceptAllProposals", "top-of-file accept-all routes at the batch command");
+    assert.strictEqual(rejectAll.command, "cowriting.rejectAllProposals", "top-of-file reject-all routes at the batch command");
+    assert.deepStrictEqual(acceptAll.arguments, undefined, "acceptAllProposals takes no arguments (targets the active editor)");
+  });
+});