A season marked watched, a pull from Plex and a YouTube resume point made their first row by a read
then an add, and failed on the unique key when a first checkpoint or the watched mark made it in
between. They go through the same insert-then-read as the checkpoint (the resume point is one
upsert); a pull that meets a local change still waiting for its push leaves it.
Folding duplicate Watch later lists moved their videos but not a Home pin, which the cascade then
deleted; the first pin of a dropped copy moves onto the kept list.
Marking one notice read trimmed before its own flag was flushed, so the trim left one past the cap.
The route test now crosses the cap and reads the result from a session of its own.
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).
peter