fix: enable SQLite WAL mode to prevent database locking errors

Fixes race condition causing "database is locked" errors during concurrent
writes to SQLite, particularly in streaming responses with guardrails where
multiple inference calls write simultaneously.

Enable Write-Ahead Logging (WAL) mode for SQLite which allows multiple
concurrent readers and one writer without blocking. Set busy_timeout to 5s
so SQLite retries instead of failing immediately. Remove the logic that
disabled write queues for SQLite since WAL mode eliminates the locking
issues that prompted disabling them.

Fixes: test_output_safety_guardrails_safe_content[stream=True] flake

src/llama_stack/providers/utils/inference/inference_store.py

@@ -47,14 +47,6 @@ class InferenceStore:
         base_store = sqlstore_impl(self.reference)
         self.sql_store = AuthorizedSqlStore(base_store, self.policy)
 
-        # Disable write queue for SQLite to avoid concurrency issues
-        backend_name = self.reference.backend
-        backend_config = _SQLSTORE_BACKENDS.get(backend_name)
-        if backend_config is None:
-            raise ValueError(
-                f"Unregistered SQL backend '{backend_name}'. Registered backends: {sorted(_SQLSTORE_BACKENDS)}"
-            )
-        self.enable_write_queue = backend_config.type != StorageBackendType.SQL_SQLITE
         await self.sql_store.create_table(
             "chat_completions",
             {
@@ -70,8 +62,9 @@ class InferenceStore:
             self._queue = asyncio.Queue(maxsize=self._max_write_queue_size)
             for _ in range(self._num_writers):
                 self._worker_tasks.append(asyncio.create_task(self._worker_loop()))
-        else:
+            logger.debug(
-            logger.info("Write queue disabled for SQLite to avoid concurrency issues")
+                f"Inference store write queue enabled with {self._num_writers} writers, max queue size {self._max_write_queue_size}"
+            )
 
     async def shutdown(self) -> None:
         if not self._worker_tasks:

src/llama_stack/providers/utils/responses/responses_store.py

@@ -70,13 +70,6 @@ class ResponsesStore:
         base_store = sqlstore_impl(self.reference)
         self.sql_store = AuthorizedSqlStore(base_store, self.policy)
 
-        backend_config = _SQLSTORE_BACKENDS.get(self.reference.backend)
-        if backend_config is None:
-            raise ValueError(
-                f"Unregistered SQL backend '{self.reference.backend}'. Registered backends: {sorted(_SQLSTORE_BACKENDS)}"
-            )
-        if backend_config.type == StorageBackendType.SQL_SQLITE:
-            self.enable_write_queue = False
         await self.sql_store.create_table(
             "openai_responses",
             {
@@ -99,8 +92,9 @@ class ResponsesStore:
             self._queue = asyncio.Queue(maxsize=self._max_write_queue_size)
             for _ in range(self._num_writers):
                 self._worker_tasks.append(asyncio.create_task(self._worker_loop()))
-        else:
+            logger.debug(
-            logger.debug("Write queue disabled for SQLite to avoid concurrency issues")
+                f"Responses store write queue enabled with {self._num_writers} writers, max queue size {self._max_write_queue_size}"
+            )
 
     async def shutdown(self) -> None:
         if not self._worker_tasks:

src/llama_stack/providers/utils/sqlstore/sqlalchemy_sqlstore.py

@@ -17,6 +17,7 @@ from sqlalchemy import (
     String,
     Table,
     Text,
+    event,
     inspect,
     select,
     text,
@@ -75,7 +76,36 @@ class SqlAlchemySqlStoreImpl(SqlStore):
         self.metadata = MetaData()
 
     def create_engine(self) -> AsyncEngine:
-        return create_async_engine(self.config.engine_str, pool_pre_ping=True)
+        # Configure connection args for better concurrency support
+        connect_args = {}
+        if "sqlite" in self.config.engine_str:
+            # SQLite-specific optimizations for concurrent access
+            # With WAL mode, most locks resolve in milliseconds, but allow up to 5s for edge cases
+            connect_args["timeout"] = 5.0
+            connect_args["check_same_thread"] = False  # Allow usage across asyncio tasks
+
+        engine = create_async_engine(
+            self.config.engine_str,
+            pool_pre_ping=True,
+            connect_args=connect_args,
+        )
+
+        # Enable WAL mode for SQLite to support concurrent readers and writers
+        if "sqlite" in self.config.engine_str:
+
+            @event.listens_for(engine.sync_engine, "connect")
+            def set_sqlite_pragma(dbapi_conn, connection_record):
+                cursor = dbapi_conn.cursor()
+                # Enable Write-Ahead Logging for better concurrency
+                cursor.execute("PRAGMA journal_mode=WAL")
+                # Set busy timeout to 5 seconds (retry instead of immediate failure)
+                # With WAL mode, locks should be brief; if we hit 5s there's a bigger issue
+                cursor.execute("PRAGMA busy_timeout=5000")
+                # Use NORMAL synchronous mode for better performance (still safe with WAL)
+                cursor.execute("PRAGMA synchronous=NORMAL")
+                cursor.close()
+
+        return engine
 
     async def create_table(
         self,