fix(e2e): persist the winning A1 body snippet for post-restart

UI-13b already made A1 the durable document, but phase-state still expected the UI-06 marker. Record successful saves as the latest snippet, ignore conflict drafts, and write that final value at UI-15-pre without relaxing the restore assertion.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/e2e/document-revision-runtime.spec.ts

@@ -28,6 +28,7 @@ import {
   SHARED_PHASE_STATE_FILE,
   playwrightResultsFileName,
 } from '../src/lib/playwrightPhaseArtifacts';
+import { nextDurableBodySnippet } from '../src/lib/durableBodySnippet';
 
 /**
  * Document revision runtime — real UI acceptance (UI-01..UI-16).
@@ -670,6 +671,8 @@ test.describe.serial('document-revision-runtime UI acceptance', () => {
   let secondDocTitle = '';
   let secondDocId = '';
   let uploadedDocId = '';
+  /** Latest server-durable body marker; UI-15-pre writes this as bodySnippet. */
+  let latestDurableBodySnippet = '';
 
   test.beforeAll(async ({ browser }) => {
     context = await browser.newContext();
@@ -1047,8 +1050,12 @@ test.describe.serial('document-revision-runtime UI acceptance', () => {
       timeout: 30_000,
     });
     await shot(page, 'UI-06-after-refresh.png');
+    latestDurableBodySnippet = nextDurableBodySnippet(latestDurableBodySnippet, {
+      kind: 'persisted',
+      snippet: marker,
+    }) || marker;
     const st = readPhaseState();
-    writePhaseState({ ...st, bodySnippet: marker, revisionText: r1 });
+    writePhaseState({ ...st, bodySnippet: latestDurableBodySnippet, revisionText: r1 });
     recordPass({
       id: 'UI-06',
       name: 'save + hard refresh',
@@ -1386,6 +1393,15 @@ test.describe.serial('document-revision-runtime UI acceptance', () => {
     await expect(page.getByText(markerA2)).toHaveCount(0);
     await shot(pageA2, 'UI-13b-conflict-A2.png');
     await ctxA2.close();
+    latestDurableBodySnippet = nextDurableBodySnippet(latestDurableBodySnippet, {
+      kind: 'persisted',
+      snippet: markerA1,
+    }) || markerA1;
+    latestDurableBodySnippet = nextDurableBodySnippet(latestDurableBodySnippet, {
+      kind: 'conflict_draft',
+      snippet: markerA2,
+    }) || latestDurableBodySnippet;
+    writePhaseState({ ...readPhaseState(), bodySnippet: latestDurableBodySnippet });
     recordPass({
       id: 'UI-13b',
       name: 'author A/A head conflict',
@@ -1448,6 +1464,7 @@ test.describe.serial('document-revision-runtime UI acceptance', () => {
       controlledDocId,
       versionText: v,
       revisionText: r,
+      bodySnippet: latestDurableBodySnippet || st.bodySnippet,
       userA: USER_A,
       userB: USER_B,
       userC: USER_C,

web/src/lib/durableBodySnippet.test.ts

@@ -0,0 +1,33 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import { nextDurableBodySnippet, requireDurableSnippet } from './durableBodySnippet';
+
+describe('durableBodySnippet', () => {
+  it('rejects empty persisted snippets', () => {
+    assert.throws(() => requireDurableSnippet('  '), /empty_durable_body_snippet/);
+    assert.throws(
+      () => nextDurableBodySnippet('UI06-old', { kind: 'persisted', snippet: '   ' }),
+      /empty_durable_body_snippet/,
+    );
+  });
+
+  it('lets a later successful revision replace the old snippet', () => {
+    const afterUi06 = nextDurableBodySnippet(undefined, { kind: 'persisted', snippet: ' UI06-mu0eq020 ' });
+    assert.equal(afterUi06, 'UI06-mu0eq020');
+    const afterA1 = nextDurableBodySnippet(afterUi06, { kind: 'persisted', snippet: 'A1-win-mu0eq020' });
+    assert.equal(afterA1, 'A1-win-mu0eq020');
+    assert.notEqual(afterA1, afterUi06);
+  });
+
+  it('does not promote a conflict-failed draft to the expected body', () => {
+    const afterUi06 = nextDurableBodySnippet(undefined, { kind: 'persisted', snippet: 'UI06-mu0eq020' });
+    const afterA1 = nextDurableBodySnippet(afterUi06, { kind: 'persisted', snippet: 'A1-win-mu0eq020' });
+    const afterA2Conflict = nextDurableBodySnippet(afterA1, {
+      kind: 'conflict_draft',
+      snippet: 'A2-conflict-mu0eq020',
+    });
+    assert.equal(afterA2Conflict, 'A1-win-mu0eq020');
+    assert.notEqual(afterA2Conflict, 'A2-conflict-mu0eq020');
+    assert.notEqual(afterA2Conflict, 'UI06-mu0eq020');
+  });
+});

web/src/lib/durableBodySnippet.ts

@@ -0,0 +1,26 @@
+export type DurableBodyEvent =
+  | { kind: 'persisted'; snippet: string }
+  | { kind: 'conflict_draft'; snippet: string };
+
+export function requireDurableSnippet(snippet: string): string {
+  const next = snippet.trim();
+  if (!next) {
+    throw new Error('empty_durable_body_snippet');
+  }
+  return next;
+}
+
+/**
+ * Latest server-durable body snippet for post-restart.
+ * A later successful save replaces the previous snippet.
+ * A conflict-failed editor draft never becomes the expected body.
+ */
+export function nextDurableBodySnippet(
+  current: string | undefined,
+  event: DurableBodyEvent,
+): string | undefined {
+  if (event.kind === 'conflict_draft') {
+    return current;
+  }
+  return requireDurableSnippet(event.snippet);
+}