tryAcquireDbLock now acquires via engine.executeRaw (signal-boundable)
and releases via engine.executeRawDirect instead of the sql tagged
template. The fixture's mock engine returned [] from executeRaw, so
every spawned supervisor failed lock acquisition and exited LOCK_HELD
(2), breaking all 8 supervisor integration tests. The mock now returns
the lock row for gbrain_cycle_locks queries and stubs executeRawDirect.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>