Gmail label sync + no-dup backfill, live label/UI updates, account-delete cleanup, Sync-SPAM toggle, sidebar logo

Gmail sync (SPEC: Gmail sync):
- Provider fetches X-GM-LABELS when X-GM-EXT-1 is advertised; parses custom labels
  (system labels dropped, mUTF-7 decoded) onto RemoteMessage.
- Engine syncs only system folders + All Mail for Gmail, skips every label folder,
  and dedupes the All Mail pass by Message-ID — kills the INBOX/All-Mail duplication.
- Custom labels ride the message.new event; the labels plugin subscribes and maps
  them to chips as "<name> [Gmail]" (per-message + thread aggregate + known set),
  so labels fill in gradually with the sync window. Non-ASCII labels decode right.

Labels self-healing (message-driven reconcile):
- Per-message keys are the source of truth; t: aggregates and _labels are derived.
  Reconcile drops labels of deleted messages, regroups survivors by their current
  thread (fixing JWZ thread merges), rewrites changed t: keys, and rebuilds _labels
  from live messages — keeping user labels, dropping orphaned Gmail ones.
- New SDK reads: sdk.threads.existing / sdk.messages.threads_of. Sidebar refreshes
  live via a plugin.labels.changed WS event on new labels.

Account deletion: prune threads left empty after the cascade (they were user-scoped,
so only messages cascaded) + de-list the account from surviving cross-account threads.

Sync SPAM: opt-in per-account sync_spam (migration 0015, default off) — the engine
skips the Junk folder in backfill and poll unless enabled; wizard checkbox added.

Robustness / UX:
- WebSocket auto-reconnects with backoff and resyncs on (re)connect, and account
  add/delete invalidates threads/labels — no more hard refresh for live updates.
- Backfill banner + sidebar ring also require done < total, so a completed account
  can't leave a stuck "X of X".
- Scrub lone UTF-16 surrogates from parsed headers/bodies so bad messages no longer
  crash the backfill on Postgres text/JSONB.
- Ultimo signet logo in the Mail/Calendar/Contacts sidebar header (and at the top of
  the collapsed rail), via the shared plugin-ui.css + MailLayout.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U72FZiF1W1pb8XxyWBTREA

backend/tests/accounts/test_account_api.py

@@ -19,7 +19,7 @@ from app.config import get_settings
 from app.identity.passwords import hash_password
 from app.identity.sessions import create_session
 from app.main import create_app
-from app.models import Account, User
+from app.models import Account, Thread, User
 
 CSRF = "test-csrf-token"
 GOOD_CFG = {
@@ -281,3 +281,46 @@ async def test_delete_account(ctx: Ctx, monkeypatch) -> None:  # type: ignore[no
 
     gone = await ctx.session.scalar(select(Account).where(Account.id == uuid.UUID(account_id)))
     assert gone is None
+
+
+async def test_delete_account_prunes_orphaned_threads(ctx: Ctx, monkeypatch) -> None:  # type: ignore[no-untyped-def]
+    """Deleting an account removes threads left with no messages (else the unified
+    list / label views show empty rows that can't be opened)."""
+    import datetime as dt
+
+    async def fake_test(**_kw: object) -> None:
+        return None
+
+    class FakePool:
+        async def enqueue_job(self, name: str, arg: str, **kwargs: object) -> None:
+            return None
+
+    async def fake_pool() -> FakePool:
+        return FakePool()
+
+    monkeypatch.setattr(accounts_api, "test_account", fake_test)
+    monkeypatch.setattr(app_queue, "get_arq_pool", fake_pool)
+
+    created = await ctx.client.post(
+        "/api/accounts",
+        json={**GOOD_CFG, "email": "orphan@example.com", "password": "secret"},
+        headers=_hdr(),
+    )
+    account_id = uuid.UUID(created.json()["id"])
+    # An empty thread tagged to this account (message-less, as after a cascade delete).
+    thread_id = uuid.uuid4()
+    ctx.session.add(
+        Thread(
+            id=thread_id,
+            user_id=ctx.user_id,
+            subject_norm="orphan",
+            last_message_at=dt.datetime.now(dt.UTC),
+            account_ids=[account_id],
+        )
+    )
+    await ctx.session.commit()
+    ctx.session.expunge_all()  # force the assertion query to hit the DB
+
+    resp = await ctx.client.request("DELETE", f"/api/accounts/{account_id}", headers=_hdr())
+    assert resp.status_code == 200
+    assert await ctx.session.scalar(select(Thread).where(Thread.id == thread_id)) is None