Production corruption #6 left b-tree pages with zeroed headers but intact old cell content — the Bug E pattern. This fix applies three pragma calls on every connect():
- synchronous=FULL (was NORMAL): closes the WAL-checkpoint reordering window where a crash between WAL commit and main-DB write leaves a partially-written b-tree page header. Cost is <1ms per commit on local SSD; negligible at kanban write volume.
- secure_delete=ON: forces SQLite to zero freed page bytes on disk. If a torn write or hardware fault later corrupts a page, the underlying cell content is zero, so corruption is detectable and no stale rows can resurface as live data.
- cell_size_check=ON: adds a read-side guard so corrupt cells surface as errors at read time rather than as silent wrong-data returns.
All three are connection-scoped and re-applied on every connect(). secure_delete also writes a persistent flag into the DB header on the first call against a fresh DB, making the protection durable across processes for new DBs.
Tests added for all four required cases: each pragma active on a fresh connection, and all three re-applied after close+reopen. Also adds the required negative test (migration path does not reset pragmas).
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