The worker's status claims success only on its first frame (improvise-i0v9)

The worker transport wrote "in-page worker · <doc>" when it spawned the
worker, before anything had answered, so a tab whose worker could not start
showed a success-looking status over a blank page. It now writes "starting
the worker · <doc>…", and createShell's arm() takes an `answer` that sawFrame
writes on the first frame, but only while the watchdog is still armed. A
ReadOnly or SeedMissing notice lands BEFORE the Snapshot, and fail() has
already disarmed, so the claim cannot overwrite the precise reason.

The two-tab spec now logs every #status and denies both the premature claim
and "did not answer" before the page clock is walked. A new spec pins the
exact status sequence on the writable path. Reasoning:
context/code/clients.md, "The watchdog".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

web/tests/shell.test.js

@@ -351,6 +351,43 @@ test("a notice DISARMS the watchdog rather than being replaced by it", () => {
   );
 });
 
+// improvise-i0v9: "in-page worker · <doc>" was written before the worker had
+// answered anything, and read as success over a blank page for eight seconds.
+test("only the first frame claims the peer answered, and not before it", () => {
+  const clock = fakeClock();
+  const seen = [];
+  const shell = createShell({
+    onShell: (t) => seen.push(t),
+    timeoutMs: 8000,
+    setTimer: clock.setTimer,
+    clearTimer: clock.clearTimer,
+  });
+  shell.arm("did not answer", { answer: "in-page worker · a.improv" });
+  assert.deepEqual(seen, [], "the claim was made before any frame arrived");
+  shell.sawFrame();
+  shell.sawFrame();
+  assert.deepEqual(seen, ["in-page worker · a.improv"]);
+});
+
+// The order worker.js really produces on a locked document: the ReadOnly
+// notice is posted after `start()` and BEFORE the Snapshot answers the handshake.
+test("a reason given before the first frame is not replaced by the frame's claim", () => {
+  const clock = fakeClock();
+  const seen = [];
+  const shell = createShell({
+    onShell: (t) => seen.push(t),
+    timeoutMs: 8000,
+    setTimer: clock.setTimer,
+    clearTimer: clock.clearTimer,
+  });
+  shell.arm("did not answer", { answer: "in-page worker · a.improv" });
+  shell.fail(noticeText({ kind: "ReadOnly", document: "a.improv", detail: "" }));
+  shell.sawFrame();
+  clock.fire();
+  assert.equal(seen.length, 1, `#status said: ${JSON.stringify(seen)}`);
+  assert.match(seen[0], /read-only/);
+});
+
 // The notice's remembered state. The value crosses `localStorage`, which is
 // allowed to forget and allowed to throw, so the interesting inputs are the
 // ones that are NOT either spelling.