test(supervisor): update runner fixture mock for #2750 lock path

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>

test/fixtures/supervisor-runner.ts

@@ -24,15 +24,18 @@ import type { BrainEngine } from '../../src/core/engine.ts';
 // Mock engine: healthCheck() calls engine.executeRaw; return empty rows so
 // the query path exercises without needing Postgres.
 //
-// #1849: start() now acquires the queue-scoped DB singleton lock via
-// tryAcquireDbLock, which uses the postgres `sql` tagged-template escape hatch.
-// The stub returns a single row from every call so acquire succeeds (length 1
-// → acquired) and refresh/release are no-ops. Each spawned runner is a fresh
-// process, so there's no cross-test lock state to clean up.
+// #1849: start() acquires the queue-scoped DB singleton lock via
+// tryAcquireDbLock. #2750 routed the acquire upsert through engine.executeRaw
+// (signal-boundable) and release through engine.executeRawDirect, so the
+// stub returns a single row from the lock upsert (length 1 → acquired) and
+// empty rows everywhere else. Each spawned runner is a fresh process, so
+// there's no cross-test lock state to clean up.
 const sqlStub = (..._args: unknown[]) => Promise.resolve([{ id: 'supervisor-lock' }]);
 const mockEngine: Partial<BrainEngine> = {
   kind: 'postgres' as const,
-  executeRaw: async () => [],
+  executeRaw: async (query: string) =>
+    query.includes('gbrain_cycle_locks') ? [{ id: 'supervisor-lock' }] : [],
+  executeRawDirect: async () => [],
   sql: sqlStub,
 } as unknown as BrainEngine;