Background Save Scheduling with Dirty-Flag Discipline
Adds AtomicBool dirty/save_pending fields, storm-prevention via optimistic stamp, and Weak<HnswProvider> drop semantics for background HNSW persistence scheduling.
v1.7.32026-06-21
·schedule_save no-ops when dirty=false and de-duplicates concurrent callers via save_pending swap
·Weak<HnswProvider> in closure — drop before quiescence loses in-memory state cleanly, no panic, no partial files
·Store::schedule_task added as public scheduling surface (CP-D2-3: BackgroundExecutor::spawn is pub(crate))