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/app/indexer/indexer.py

@@ -36,6 +36,7 @@ class PersistResult:
     message: Message
     search_doc: SearchDoc
     has_remote_images: bool
+    gmail_labels: tuple[str, ...] = ()
 
 
 def _epoch(value: datetime) -> int:
@@ -140,8 +141,13 @@ async def persist_message(
     mailbox_id: uuid.UUID,
     mailbox_special_use: str | None,
     remote: RemoteMessage,
+    dedupe_account_scope: bool = False,
 ) -> PersistResult | None:
-    """Persist one message. Returns None if it already exists (idempotent)."""
+    """Persist one message. Returns None if it already exists (idempotent).
+
+    ``dedupe_account_scope`` skips a message already stored under a *different*
+    mailbox of the same account (same Message-ID) — used for Gmail's All Mail pass so
+    a message already synced from INBOX/Sent isn't duplicated (SPEC: Gmail sync)."""
     existing = await session.scalar(
         select(Message.id).where(Message.mailbox_id == mailbox_id, Message.uid == remote.uid)
     )
@@ -154,6 +160,18 @@ async def persist_message(
     message_id_hdr = await _resolve_message_id(
         session, user_id=user_id, account_id=account_id, parsed_id=parsed.message_id, raw=remote.raw
     )
+    if dedupe_account_scope and message_id_hdr is not None:
+        dup = await session.scalar(
+            select(Message.id)
+            .where(
+                Message.account_id == account_id,
+                Message.message_id_hdr == message_id_hdr,
+                Message.mailbox_id != mailbox_id,
+            )
+            .limit(1)
+        )
+        if dup is not None:
+            return None
     message = Message(
         id=uuid.uuid4(),
         user_id=user_id,
@@ -223,4 +241,9 @@ async def persist_message(
 
     await session.flush()
     doc = _build_search_doc(message, parsed, mailbox_special_use)
-    return PersistResult(message=message, search_doc=doc, has_remote_images=has_remote_images)
+    return PersistResult(
+        message=message,
+        search_doc=doc,
+        has_remote_images=has_remote_images,
+        gmail_labels=remote.gmail_labels,
+    )