fix: advisory lock in initSchema() prevents deadlock on concurrent DDL

When multiple processes call initSchema() concurrently (e.g., test setup +
CLI subprocess, or parallel workers during E2E tests), the schema SQL's
DROP TRIGGER + CREATE TRIGGER statements acquire AccessExclusiveLock on
different tables, causing deadlocks.

Fix: pg_advisory_lock(42) serializes all initSchema() calls within the
same database. The lock is session-scoped and released in a finally block.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/core/db.ts

@@ -60,7 +60,13 @@ export async function disconnect(): Promise<void> {
 
 export async function initSchema(): Promise<void> {
   const conn = getConnection();
-  await conn.unsafe(SCHEMA_SQL);
+  // Advisory lock prevents concurrent initSchema() calls from deadlocking
+  await conn`SELECT pg_advisory_lock(42)`;
+  try {
+    await conn.unsafe(SCHEMA_SQL);
+  } finally {
+    await conn`SELECT pg_advisory_unlock(42)`;
+  }
 }
 
 export async function withTransaction<T>(fn: (tx: ReturnType<typeof postgres>) => Promise<T>): Promise<T> {

src/core/postgres-engine.ts

@@ -57,12 +57,19 @@ export class PostgresEngine implements BrainEngine {
 
   async initSchema(): Promise<void> {
     const conn = this.sql;
-    await conn.unsafe(SCHEMA_SQL);
+    // Advisory lock prevents concurrent initSchema() calls from deadlocking
+    // on DDL statements (DROP TRIGGER + CREATE TRIGGER acquire AccessExclusiveLock)
+    await conn`SELECT pg_advisory_lock(42)`;
+    try {
+      await conn.unsafe(SCHEMA_SQL);
 
-    // Run any pending migrations automatically
-    const { applied } = await runMigrations(this);
-    if (applied > 0) {
-      console.log(`  ${applied} migration(s) applied`);
+      // Run any pending migrations automatically
+      const { applied } = await runMigrations(this);
+      if (applied > 0) {
+        console.log(`  ${applied} migration(s) applied`);
+      }
+    } finally {
+      await conn`SELECT pg_advisory_unlock(42)`;
     }
   }