fix: task runs record the lane Celery really routes them to, and no healthy long job is swept as stalled (#4432)

celery_signals._queue_for was a hand-kept copy of task_routes and had
drifted:

- backup, admin and library_audit jobs, and backfill_phash, run on
  maintenance_long but were recorded as `maintenance`;
- translation and gpu_queue jobs were recorded as `default`, where the
  5-minute stall sweep failed healthy 35-minute translation runs.

It now asks the router, cached per task name.

A new guard test checks every registered task's hard time limit against
the stall threshold the sweep would use for it. It also caught these
sweeps, which failed healthy runs mid-flight and are fixed here:

- ml's scheduled sweeps (35 min, previously swept at 25);
- train_heads and apply_head_tags (65 min);
- import_media_file (6 min, previously swept at 5);
- the long lane, which now has its own 45-minute threshold.

UI changes:

- the admin job poller follows a job by celery_task_id, via a new filter
  on /runs, instead of by lane;
- the archive re-extract and missing-file repair cards show the long
  lane's backlog, where their jobs actually wait;
- the queue table lists maintenance_long.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

backend/app/celery_signals.py

@@ -18,6 +18,7 @@ dark for that interval. Monitoring NEVER breaks the thing it's
 monitoring.
 """
 
+import functools
 import logging
 from datetime import UTC, datetime
 
@@ -53,42 +54,29 @@ _INT32_MIN = -2_147_483_648
 
 
 def _queue_for(task) -> str:
-    """Reverse the task→queue routing from celery_app.task_routes.
-    Keep in sync if task_routes is reordered.
+    """The queue Celery routes this task to — asked of the router itself.
 
-    Audit 2026-06-02: backup/admin/library_audit prefixes were
-    missing here even though task_routes sent all three to
-    'maintenance'. The TaskRun.queue column then lied for those
-    rows (claimed 'default') so per-queue dashboard filters and
-    per-queue threshold overrides silently missed them.
+    This was a hand-kept copy of `celery_app.task_routes`, and it drifted
+    twice (the 2026-06-02 audit, then #4432). Long-lane jobs were recorded as
+    `maintenance`, and translation and gpu_queue runs as `default`, where the
+    5-minute stall sweep failed healthy 35-minute translation runs. The router
+    answers from the same table the broker uses, so the two cannot disagree.
     """
     name = getattr(task, "name", "") or ""
-    if name.startswith("backend.app.tasks.import_file."):
-        return "import"
-    if name.startswith("backend.app.tasks.ml."):
-        return "ml"
-    if name.startswith("backend.app.tasks.thumbnail."):
-        return "thumbnail"
-    if name.startswith((
-        "backend.app.tasks.download.",
-        # External file-host fetches share the download lane (celery_app
-        # routes external.* → download). Mirror it here or TaskRun.queue
-        # lies 'default' for them, so per-queue dashboard filters and the
-        # per-queue threshold override miss them — the same gap the
-        # 2026-06-02 audit fixed for backup/admin/library_audit.
-        "backend.app.tasks.external.",
-    )):
-        return "download"
-    if name.startswith("backend.app.tasks.scan."):
-        return "scan"
-    if name.startswith((
-        "backend.app.tasks.maintenance.",
-        "backend.app.tasks.backup.",
-        "backend.app.tasks.admin.",
-        "backend.app.tasks.library_audit.",
-    )):
-        return "maintenance"
-    return "default"
+    app = getattr(task, "app", None)
+    if app is None:
+        from .celery_app import celery as app
+    return _routed_queue(app, name)
+
+
+@functools.lru_cache(maxsize=1024)
+def _routed_queue(app, name: str) -> str:
+    try:
+        queue = app.amqp.router.route({}, name).get("queue")
+    except Exception:  # noqa: BLE001 — monitoring never breaks the task
+        log.warning("task_run: could not resolve the queue for %s", name)
+        return "default"
+    return getattr(queue, "name", None) or (queue if isinstance(queue, str) else "default")
 
 
 def _target_id_from_args(args) -> int | None: