fix: signing in again as the same person in another tab no longer freezes this one

The account boundary reloads a tab when the shared session changes under
it — the guard against one account's tab showing another account's data.
A second tab signing in as the same person is a new session, not a new
account; it is adopted, and the reload is kept for a different owner or
none. "Your account session changed. Reload to continue safely" now means
what it says.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Dv6sqaY6Vq3ChZHMem3cnU

test/account-boundary.test.js

@@ -1118,3 +1118,22 @@ test('a transient passive owner read failure cannot be mistaken for absent owner
     assert.equal(b.reloads(), 0);
   } finally { b.close(); }
 });
+
+test('the same person signing in again in another tab is adopted, not reloaded', async () => {
+  // Opening the app in a second tab while signed in elsewhere makes a new
+  // session for the same account. The old tab used to freeze with "Your
+  // account session changed" — the message meant for a *different* account
+  // taking over the cookie. The same owner is adopted silently; a different
+  // one, or none, still reloads.
+  const b = await browser();
+  b.owner(1);
+  const shared = JSON.parse(b.w.localStorage.getItem(b.c.AccountBoundary.key));
+  b.storageMessage({ ...shared, generation: 'another-tab-same-person' });
+  assert.equal(b.c.AccountBoundary.blocked(), false, 'not frozen');
+  assert.equal(b.reloads(), 0, 'not reloaded');
+  assert.equal(b.c.AccountBoundary.capture(), 1, 'still working as the same owner');
+  b.storageMessage({ ...shared, owner: 2, generation: 'another-tab-other-person' });
+  assert.equal(b.c.AccountBoundary.blocked(), true, 'a different account still freezes this tab');
+  assert.ok(b.reloads());
+  b.close();
+});