Three fixes to the sync pipeline:
1. Atomic watermarks: wrap complete_job + update_watermark in a single
SQLite transaction so crash between them can't leave partial state.
2. Concurrent drain loops: prefetch HTTP requests via join_all (batch
size = dependent_concurrency), then write serially to DB. Reduces
~9K sequential requests from ~19 min to ~2.4 min.
3. Graceful shutdown: install Ctrl+C handler via ShutdownSignal
(Arc<AtomicBool>), thread through orchestrator/CLI, release locked
jobs on interrupt, record sync_run as "failed".
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
405e5370dc