feat(reader): a Takeout video the catalog learns later is marked watched then; the import's status

A watched video the catalog did not know at import time waits in `takeout_items`. The Shorts job now
settles those rows right after its probe (the only place a video's Short-ness becomes known), every
user's, a commit each: `reader.takeout.apply_waiting`, its count in the job's result.

`GET /api/takeout` is what the settings page reads: the user's last import run (`jobruns.last_run`)
and the kept videos by kind and outcome, "waiting" for one not known yet.

backend/app/reader/takeout.py

@@ -25,6 +25,8 @@ from contextlib import contextmanager
 from dataclasses import dataclass, field
 from datetime import datetime
 
+from sqlalchemy.orm import Session
+
 from app import quota
 from app.bodylimit import TAKEOUT_MAX_BYTES
 from app.db import SessionLocal
@@ -174,6 +176,11 @@ def _one_import(user_id: int) -> Iterator[None]:
         yield
 
 
+def run_target(user_id: int) -> str:
+    """The import run's target, `job_runs.target`: one user's import."""
+    return f"user:{user_id}"
+
+
 def run_import(user_id: int) -> dict:
     """The import job: apply what the user's kept Takeout rows can say now, as one recorded run.
     The watched part commits before the Watch later part asks YouTube for the videos the catalog
@@ -198,3 +205,20 @@ def run_import(user_id: int) -> dict:
         if outcomes.get((TakeoutKind.WATCH_LATER, None)):
             result["watch_later_waiting"] = outcomes[(TakeoutKind.WATCH_LATER, None)]
         return result
+
+
+def apply_waiting(db: Session) -> dict:
+    """Mark watched the waiting Takeout rows whose video the catalog has come to know and the Shorts
+    probe has cleared since the import — every user's, one commit each. Run after each Shorts probe
+    (the scheduler's `shorts` job), the only place a video's Short-ness becomes known. Returns its
+    counts, or an empty dict when nothing was waiting on a probed video."""
+    users = queries.takeout_users_ready(db)
+    marked = 0
+    for user_id in users:
+        user = db.get(User, user_id)
+        if user is None:
+            continue
+        with _one_import(user_id):
+            marked += service.apply_takeout_watched(db, user)["watched"]
+            db.commit()
+    return {"takeout_watched": marked} if users else {}