docs(chat): record task 3 in progress and re-lock the starter-home scroll guard on the hook

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JUei7K13cYxLHE3Axe4A45

frontend/tests/starter-questions.test.ts

@@ -206,15 +206,15 @@ test("removes the user-facing admin button from the chat page", () => {
 });
 
 test("keeps the empty starter home at the top instead of auto-scrolling", () => {
-  const autoScrollEffect = sourceBetween(
-    pageSource,
-    "useEffect(() => {\n    if (starterHomeVisible) return;",
-    "profileComplete, starterHomeVisible]);",
-  );
-
-  assert.match(autoScrollEffect, /if \(starterHomeVisible\) return/);
-  assert.match(autoScrollEffect, /const container = conversation\.current/);
-  assert.match(autoScrollEffect, /container\.scrollTo\(\{ top: container\.scrollHeight/);
+  // Former lock: a page-level effect starting `if (starterHomeVisible) return;` that called
+  // `container.scrollTo`. The follow now lives in useConversationScrollAnchor (BUG-478); the page
+  // switches it off for the starter home through the hook's `active` argument instead.
+  assert.match(pageSource, /useConversationScrollAnchor\(\n\s*conversation,\n\s*!rectificationSurfaceOpen && !starterHomeVisible,/);
+  const anchorSource = readFileSync(new URL("../src/hooks/use-conversation-scroll-anchor.ts", import.meta.url), "utf8");
+  const followEffect = anchorSource.slice(anchorSource.indexOf("// Follow: while anchored"));
+  assert.match(followEffect, /if \(!active \|\| !element\) return;/);
+  assert.ok(followEffect.indexOf("if (!active || !element) return;") < followEffect.indexOf("element.scrollTop = element.scrollHeight"));
+  assert.doesNotMatch(pageSource, /container\.scrollTo\(/);
   assert.match(pageSource, /ref=\{conversation\} className=\{`conversation/);
   assert.doesNotMatch(pageSource, /conversationEnd|scrollIntoView/);
 });