Replace OS-scheduler-dependent elapsed-time ceilings with deterministic
concurrency proofs in three tests:
- test_context_refs_concurrent: asyncio.Barrier rendezvous — all 3 URL
fetches must be in flight simultaneously before any returns.
- test_memory_boundary_commit: positive non-blocking witness — the
provider call list must still be empty when the async commit returns.
- test_mem0_v3 slow-prefetch: threading.Event park/release — prefetch
must return while the backend search is still parked.
The tests/tools/test_mcp_tool.py hunk from the original PR is dropped:
main no longer carries the 'elapsed < 2.5' assertion it targeted
(superseded by a delay-relative bound).
Salvaged from #71913.
Deep review of the cherry-picked #16454 found the ad-hoc flush thread
raced new_session()'s inline on_session_switch(reset=True): memory
providers key off internal _session_id state (MemoryManager.on_session_end
takes no session id), so a late off-thread extraction ran against
post-rotation bindings — misattributing the old transcript to the new
session id, double-ingesting the old turn buffer (supermemory), or
double-committing (openviking already async-finalizes in
on_session_switch).
Redesign: new MemoryManager.commit_session_boundary_async queues
on_session_end + on_session_switch as ONE task on the manager's existing
single-worker background executor (the same worker sync_all already
uses). This preserves the strict end→switch ordering providers depend on,
serializes against per-turn syncs FIFO, keeps /new non-blocking, and
degrades to inline (pre-#16454 behavior) when the executor is
unavailable. No ad-hoc threads; no per-provider changes needed.
The context-engine on_session_end half stays synchronous in
_launch_session_boundary_memory_flush (cheap, must land before
reset_session_state rebinds the engine).
Exit durability: _run_cleanup calls the manager's existing
flush_pending(timeout=10) barrier before shutdown, so '/new then quit'
doesn't drop the queued extraction (shutdown_all's own drain is ~5s and
cancels queued tasks). Bounded well inside the 30s exit watchdog.
Tests: ordering invariant with slow (LLM-like) extraction, FIFO
serialization vs sync_all, switch-fires-even-if-end-raises, no-provider
no-op, CLI snapshot handoff + inline-switch fallback, sync engine
boundary, cleanup flush_pending.
