When a new tenant schema is provisioned while retain/recall operations
are in-flight, run_migration() was calling synchronous migration
functions directly on the asyncio event loop. These functions execute
CREATE INDEX CONCURRENTLY, which waits for all active transactions to
commit. But in-flight asyncpg transactions cannot flush their COMMIT
because the event loop is blocked — deadlock.
Fix: wrap all four sync migration calls in asyncio.to_thread() so they
run in the thread pool, keeping the event loop free.
Reproduced with the unfixed code: test_retain_memory timed out with
httpx.ReadTimeout when run concurrently with test_create_tenant.
All 75 integration tests pass after the fix.
e0a2ac63e7