fix: final-review wave — preview host INV-10 gate, thread status+offer contextValue tokens, establish-on-open baseline, polish

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

test/e2e/suite/coediting.test.ts

@@ -1,7 +1,9 @@
 import * as assert from "node:assert";
 import * as fs from "node:fs";
 import * as path from "node:path";
+import MarkdownIt from "markdown-it";
 import * as vscode from "vscode";
+import { cowritingMarkdownItPlugin } from "../../../src/previewAnnotations";
 import { activateApi, settle, settleUntil } from "./helpers";
 
 const WS = process.env.E2E_WORKSPACE!;
@@ -143,4 +145,79 @@ suite("coediting registry (PUC-7)", () => {
     assert.strictEqual(api.proposalController.getRendered(key).length, 1, "proposal restored on re-enter");
     assert.ok(api.attributionController.getSpans(key).length >= 1, "attribution restored on re-enter");
   });
+
+  // Finding 1 (final whole-branch review, session native-surfaces-exec): the
+  // preview-annotation host's INV-10 gate must never leak one document's
+  // baseline/spans into another document's preview. The built-in preview's
+  // rendered DOM isn't queryable from a host E2E test (§6.8, mirrored from
+  // Task 7's own previewAnnotations.test.ts), so this drives the ACTUAL
+  // production `previewAnnotationHost` through a real markdown-it instance
+  // and asserts on the rendered HTML.
+  test("INV-10: a non-coedited doc's preview never inherits another doc's annotations", async () => {
+    const api = await activateApi();
+    const docA = await vscode.workspace.openTextDocument({ language: "markdown", content: "alpha original\n" });
+    await vscode.window.showTextDocument(docA);
+    await vscode.commands.executeCommand("cowriting.coeditDocument");
+    await settle();
+    const start = docA.getText().indexOf("original");
+    const okA = await vscode.commands.executeCommand<boolean>("cowriting.applyAgentEdit", {
+      uri: docA.uri.toString(),
+      start,
+      end: start + "original".length,
+      newText: "REPLACED",
+      model: "sonnet",
+      sessionId: "e2e-inv10-leak",
+      turnId: "turn-e2e-inv10-leak",
+    });
+    assert.strictEqual(okA, true, "seam edit applies to docA");
+    await settle();
+
+    // docB is opened (becomes the active editor, so it would win any
+    // `lastCoeditedUri` fallback if the gate were wrong) but NEVER entered
+    // into coediting.
+    const docB = await vscode.workspace.openTextDocument({ language: "markdown", content: "bravo untouched\n" });
+    await vscode.window.showTextDocument(docB);
+    await settle();
+
+    const md = new MarkdownIt();
+    cowritingMarkdownItPlugin(md, api.previewAnnotationHost);
+    const html = md.render(docB.getText(), { currentDocument: docB.uri });
+    assert.ok(!html.includes("cw-ins-claude"), `docB must render with no annotations, got:\n${html}`);
+    assert.ok(!html.includes("original"), `docA's baseline text must never leak into docB's preview:\n${html}`);
+    assert.ok(html.includes("bravo untouched"), "docB renders its own content unannotated");
+  });
+
+  // Finding 1, failure mode (b): `lastCoeditedUri` is never re-validated
+  // against the registry, so a doc's OWN preview stayed annotated after
+  // `stopCoediting` — an INV-10 violation for the doc whose gate was just
+  // closed, not just for a different doc.
+  test("INV-10: stopCoediting immediately clears a doc's own preview annotations", async () => {
+    const api = await activateApi();
+    const doc = await vscode.workspace.openTextDocument({ language: "markdown", content: "gamma original\n" });
+    await vscode.window.showTextDocument(doc);
+    await vscode.commands.executeCommand("cowriting.coeditDocument");
+    await settle();
+    const start = doc.getText().indexOf("original");
+    const ok = await vscode.commands.executeCommand<boolean>("cowriting.applyAgentEdit", {
+      uri: doc.uri.toString(),
+      start,
+      end: start + "original".length,
+      newText: "REPLACED",
+      model: "sonnet",
+      sessionId: "e2e-inv10-stop",
+      turnId: "turn-e2e-inv10-stop",
+    });
+    assert.strictEqual(ok, true, "seam edit applies");
+    await settle();
+
+    const md = new MarkdownIt();
+    cowritingMarkdownItPlugin(md, api.previewAnnotationHost);
+    const before = md.render(doc.getText(), { currentDocument: doc.uri });
+    assert.ok(before.includes("cw-ins-claude"), `sanity: annotated while coediting, got:\n${before}`);
+
+    await vscode.commands.executeCommand("cowriting.stopCoediting");
+    await settle();
+    const after = md.render(doc.getText(), { currentDocument: doc.uri });
+    assert.ok(!after.includes("cw-ins-claude"), `expected a clean render after stopCoediting, got:\n${after}`);
+  });
 });