The YouTube API reads neither a user's watch history nor their Watch later list, so the Takeout
export is the only way in. `POST /api/takeout` takes one file of it (watch-history.json or
Watch later-videos.csv, told apart by content), keeps its videos in `takeout_items` and queues the
user's `takeout_import` run, whose outcome reaches their inbox.
The run marks watched the known videos the Shorts probe has cleared, at the Takeout time; a Short
is not marked, and a state the user set here (watched, hidden, or changed after that time) wins, by
the upsert's own condition. A video the catalog does not know yet waits with no outcome. Watch later
videos are fetched if unknown and appended oldest first.
An ad-hoc run can now ask for a completion notice (`run_ad_hoc(..., notify=True)`).
The first checkpoint of an item and the final flush beside it both read no
state and both inserted; the loser failed on uq_plex_user_item. Two first saves
each made a Watch later list. Both are created by an ON CONFLICT DO NOTHING
insert and then read; a partial unique index holds one Watch later per user, and
the migration folds an existing second list into the first. Plex keeps one
per-item state map (rollup.item_state_map).
VideoState, Playlist, PlaylistItem, SavedView, ComfortPin, Tag and ChannelTag leave app/models.py
for app/reader/models.py; app.tables registers them. No schema change.
peter