Closes a P0 step-8 test gap. Drives SaveScheduler with a recording
EditorRepository subclass (real in-memory ffi db only to satisfy the ctor) and
pins: flush writes immediately; rapid schedules coalesce to ONE debounced write
with the latest snapshot; the captured snapshot is isolated from later mutation
of the source list; distinct hosts flush independently; dispose cancels a
pending write; schedule-after-dispose is a no-op.
flutter analyze clean; 6/6 new, 84/84 total.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
