"Sync to YouTube" was a one-directional destructive push (local wins, deletes
from YouTube every item not in the local list), so items added on YouTube were
lost and a dirty pull was skipped entirely. Replace it with a real 3-way merge:
each item is classified against the last-synced baseline as a local-add, a
YouTube-add, or a genuine delete, so an add or delete on either side survives.
- Persist the ordered baseline id set (new playlists.synced_video_ids, migration
0075); the fingerprint hash alone couldn't drive a merge. NULL baseline (fresh
export / pre-S7 link) unions losslessly on the first sync and records one.
- Pure merge_plan(baseline, local, youtube) -> add/remove per side + merged order
(local order, YouTube-only additions appended). merge_playlist applies the
local side directly and the YouTube side through the failure breaker; the
baseline only advances on full success so a partial failure re-converges.
- plan_merge/push-plan now report what each side gains and loses; the confirm
dialog shows the two-way plan before applying (pushPlanMerge, HU+EN).
- Tests: 10 new (pure classification incl. delete-vs-stale-copy; DB apply proving
a YouTube-add and a Siftlode-add both survive on both sides, a genuine delete
propagates without collateral loss, no-baseline never deletes, create path).
peter
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