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/providers/imap_smtp/provider.py

@@ -31,6 +31,7 @@ from app.providers.base import (
     RemoteMessage,
 )
 from app.providers.imap_smtp.parsing import (
+    encode_mailbox_name,
     parse_fetch_lines,
     parse_list_line,
     parse_search_uids,
@@ -39,6 +40,9 @@ from app.providers.imap_smtp.parsing import (
 )
 
 _FETCH_ITEMS = "(UID FLAGS INTERNALDATE RFC822.SIZE BODY.PEEK[])"
+# Gmail (X-GM-EXT-1): also pull each message's labels so custom labels can map to
+# chips without visiting every label folder (SPEC: Gmail sync / no-duplication).
+_FETCH_ITEMS_GM = "(UID FLAGS INTERNALDATE RFC822.SIZE X-GM-LABELS BODY.PEEK[])"
 _IDLE_TIMEOUT = 25 * 60  # SPEC §5.1: re-issue IDLE at least every 25 min
 _CONNECT_TIMEOUT = 20
 _PER_ACCOUNT_CONN_CAP = 4  # SPEC §6.3 / §4: IDLE + transient + short-lived jobs
@@ -81,6 +85,13 @@ class ImapSmtpProvider(MailProvider):
         self._uidvalidity_seen: dict[str, int] = {}
         self._conn_slots: list[asyncio.Semaphore] = []
         self._qresync_enabled = False
+        self._gm_ext = False
+
+    @property
+    def gmail_labels_supported(self) -> bool:
+        """True when the server advertises ``X-GM-EXT-1`` (Gmail), so FETCH can pull
+        ``X-GM-LABELS`` and the engine can use the no-duplication Gmail sync path."""
+        return self._gm_ext
 
     @property
     def qresync_enabled(self) -> bool:
@@ -148,6 +159,8 @@ class ImapSmtpProvider(MailProvider):
             self._release_conn_slots()  # never hold a slot without an open socket
             raise
         self._imap = imap
+        caps = {c.upper() for c in (imap.protocol.capabilities or set())}
+        self._gm_ext = "X-GM-EXT-1" in caps
         await self._maybe_enable_qresync(imap)
         return imap
 
@@ -165,9 +178,16 @@ class ImapSmtpProvider(MailProvider):
         except Exception:  # noqa: BLE001 - degrade gracefully to the reconcile path
             self._qresync_enabled = False
 
+    @staticmethod
+    def _wire(mailbox: str) -> str:
+        """Server wire form of a mailbox name: mUTF-7 encoded and quoted. Handles
+        non-ASCII names (Gmail's localized ``[Gmail]/Wysłane``) and names with
+        spaces (``[Gmail]/All Mail``); ASCII names are unchanged bar the quotes."""
+        return str(aioimaplib.quoted(encode_mailbox_name(mailbox)))
+
     async def _select(self, mailbox: str) -> dict[str, int]:
         imap = await self._connect()
-        resp = await imap.select(mailbox)
+        resp = await imap.select(self._wire(mailbox))
         if resp.result != "OK":
             raise ProviderConnectError(f"cannot select {mailbox!r}")
         self._selected = mailbox
@@ -212,7 +232,7 @@ class ImapSmtpProvider(MailProvider):
     async def _mailbox_uidvalidity(self, path: str) -> int:
         imap = await self._connect()
         try:
-            resp = await imap.status(path, "(UIDVALIDITY)")
+            resp = await imap.status(self._wire(path), "(UIDVALIDITY)")
         except Exception:
             return 0
         if resp.result != "OK":
@@ -280,7 +300,8 @@ class ImapSmtpProvider(MailProvider):
         if not uids:
             return []
         uid_set = ",".join(str(u) for u in uids)
-        resp = await imap.uid("fetch", uid_set, _FETCH_ITEMS)
+        items = _FETCH_ITEMS_GM if self._gm_ext else _FETCH_ITEMS
+        resp = await imap.uid("fetch", uid_set, items)
         if resp.result != "OK":
             raise ProviderConnectError("FETCH failed")
         out: list[RemoteMessage] = []
@@ -289,7 +310,11 @@ class ImapSmtpProvider(MailProvider):
                 continue
             out.append(
                 RemoteMessage(
-                    uid=pf.uid, raw=pf.raw, flags=pf.flags, internal_date=pf.internal_date
+                    uid=pf.uid,
+                    raw=pf.raw,
+                    flags=pf.flags,
+                    internal_date=pf.internal_date,
+                    gmail_labels=pf.gmail_labels,
                 )
             )
         return out
@@ -355,7 +380,7 @@ class ImapSmtpProvider(MailProvider):
         proto = imap.protocol
         param = f"(QRESYNC ({uidvalidity} {modseq}))"
         cmd = aioimaplib.Command(
-            "SELECT", proto.new_tag(), aioimaplib.quoted(mailbox), param, loop=proto.loop
+            "SELECT", proto.new_tag(), self._wire(mailbox), param, loop=proto.loop
         )
         return await proto.execute(cmd)
 
@@ -419,7 +444,7 @@ class ImapSmtpProvider(MailProvider):
     async def append(self, mailbox: str, raw: bytes, flags: frozenset[str]) -> int:
         imap = await self._connect()
         flag_str = f"({' '.join(sorted(flags))})" if flags else None
-        resp = await imap.append(raw, mailbox=mailbox, flags=flag_str)
+        resp = await imap.append(raw, mailbox=self._wire(mailbox), flags=flag_str)
         if resp.result != "OK":
             raise ProviderConnectError(f"APPEND to {mailbox} failed")
         for line in resp.lines: