Two bugs were causing chapters to disappear on every relaunch:
1. seedTextbookData used `try? context.save()` (swallowing errors) and
returned `inserted > 0`, so a failed save still reported success.
Callers then bumped UserDefaults textbookDataVersion and subsequent
launches skipped the re-seed entirely — with no rows on disk.
2. refreshTextbookDataIfNeeded wiped chapters via the batch-delete API
`context.delete(model: TextbookChapter.self)`, which hits the store
directly without clearing the context's .unique-id index. Re-inserting
chapters with the same ids could then throw a unique-constraint error
on save — also silently eaten by `try?`.
Fixes:
- seedTextbookData now uses do/catch around save(), returns false on
error, and verifies persistence via fetchCount before returning true.
- refreshTextbookDataIfNeeded fetches and deletes chapters individually
so the context tracks the deletion cleanly; wipe save is also now
checked and bails early on failure.
- Bumped textbookDataVersion to 11 so devices poisoned by the previous
silent-failure path retry on next launch.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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