[42lizard]

Summary

 apply Readest position
-  copy the complete firmware database to before.db
-  validate the copied identity and settings row
   open the existing firmware database read/write
   set synchronous=FULL
   BEGIN IMMEDIATE
+  validate identity and settings inside the transaction
   update exactly position + position_ts with compare-and-swap predicates
   verify one affected row and the complete resulting settings row
   COMMIT
+  record before.json, target.txt, readest-source-cfi.txt, and outcome.txt

Pre-commit failures roll back. An uncertain commit remains explicit; the next operation re-reads the firmware database and reconciles either the previous or committed position without restoring stale database contents.

Closes #29.

Evidence

• Before: each applied Readest position retained a complete before.db copy.
  After: successful, rolled-back, and uncertain transitions retain only the small text/JSON audit.
• ctest --test-dir build/readest-sync/host-linux --output-on-failure — 12/12 passed.
• Resume fault injection covers cancellation, stale observations, unsafe triggers, denied updates, post-commit audit failure, app-state failure, and both possible observations after an uncertain commit.
• docker compose run --rm qt6 make APP=readest-sync check — Qt6 ARM softfp, loader, resource format, and ABI ceilings passed.
• Two-axis code review — no Standards findings and no Spec implementation defects.
• PB743G U743g.6.11.1683: applied the pending Readest position for Beren und Lúthien, opened the native reader, returned, and reopened through Readest Sync. The audit reported committed, contained only four text/JSON files totaling 460 bytes, and created no before.db; pending state cleared and local/remote baselines converged.

Merge Danger

Door: Two-way

The change is cheap to revert and does not alter the firmware schema or the app's persisted sync format.

Blast Radius: Position apply

Only the explicit Open flow that applies a pending Readest reading position changes. Startup reads, normal native-reader handoff, and PocketBook-to-Readest uploads are unchanged.