* docs: design for syncing updated book data (cover + file) (#4544)
Cover-change sync via a content hash (coverHash = partial MD5 of cover.png)
plus a cover_updated_at field-level merge timestamp; file updates ride the
existing re-import / metaHash dedupe.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
* fix(sync): sync updated book covers across devices (#4544)
Editing a book's cover wrote cover.png locally but changed no hash (the
cover is keyed by the file hash), so peers had no signal to re-download it
and the change never propagated.
Give the cover its own content-addressed version:
- coverHash = partial MD5 of cover.png; a peer re-downloads the cover iff
the synced hash differs from the local one (idempotent, no churn on
identical/re-extracted covers — compatible with the metaHash dedupe).
- coverUpdatedAt = field-level LWW timestamp so a page-turn that wins
whole-row LWW on updated_at can't clobber a cover edit (mirrors the
reading_status_updated_at fix for #4634).
Editing a cover recomputes the hash, bumps coverUpdatedAt, and re-uploads
only the cover; the server merges cover fields independently; peers
re-download on a hash diff. File updates continue to ride the existing
re-import / metaHash dedupe (changed file -> changed hash -> re-key).
Migration 016 adds cover_hash / cover_updated_at to books.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Huang Xin
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