Refactor persistence config to use stores key with unified backends

- Add StoresConfig to group all store references under persistence.stores
- Use single 'default' backend instead of separate metadata_backend/inference_backend
- Update resolver to access persistence.stores.{metadata,inference,conversations}
- All SQLite distributions now use single store.db file with shared backend

llama_stack/core/datatypes.py

@@ -447,12 +447,9 @@ class InferenceStoreReference(StoreReference):
     )
 
 
-class PersistenceConfig(BaseModel):
-    """Unified persistence configuration."""
+class StoresConfig(BaseModel):
+    """Store references configuration."""
 
-    backends: dict[str, Annotated[KVStoreConfig | SqlStoreConfig, Field(discriminator="type")]] = Field(
-        description="Named backend configurations (e.g., 'default', 'cache')",
-    )
     metadata: StoreReference | None = Field(
         default=None,
         description="Metadata store configuration (uses KVStore backend)",
@@ -466,13 +463,28 @@ class PersistenceConfig(BaseModel):
         description="Conversations store configuration (uses SqlStore backend)",
     )
 
+
+class PersistenceConfig(BaseModel):
+    """Unified persistence configuration."""
+
+    backends: dict[str, Annotated[KVStoreConfig | SqlStoreConfig, Field(discriminator="type")]] = Field(
+        description="Named backend configurations (e.g., 'default', 'cache')",
+    )
+    stores: StoresConfig | None = Field(
+        default=None,
+        description="Store references to backends",
+    )
+
     @model_validator(mode="after")
     def validate_backend_references(self) -> Self:
         """Check all store refs point to defined backends."""
+        if not self.stores:
+            return self
+
         stores = [
-            ("metadata", self.metadata),
-            ("inference", self.inference),
-            ("conversations", self.conversations),
+            ("metadata", self.stores.metadata),
+            ("inference", self.stores.inference),
+            ("conversations", self.stores.conversations),
         ]
         for store_name, store_ref in stores:
             if store_ref and store_ref.backend not in self.backends:

llama_stack/core/persistence_resolver.py

@@ -39,7 +39,7 @@ def resolve_backend(
     Returns:
         Resolved backend config with store-specific overlays applied
     """
-    if not persistence or not store_ref:
+    if not persistence or not persistence.stores or not store_ref:
         return default_factory()
 
     backend_config = persistence.backends.get(store_ref.backend)
@@ -68,7 +68,7 @@ def resolve_inference_store_config(
     Returns:
         (sql_config, max_queue_size, num_writers)
     """
-    if not persistence or not persistence.inference:
+    if not persistence or not persistence.stores or not persistence.stores.inference:
         # Default SQLite
         return (
             SqliteSqlStoreConfig(
@@ -78,7 +78,7 @@ def resolve_inference_store_config(
             4,
         )
 
-    inference_ref = persistence.inference
+    inference_ref = persistence.stores.inference
     backend_config = persistence.backends.get(inference_ref.backend)
     if not backend_config:
         raise ValueError(
@@ -116,9 +116,13 @@ def resolve_metadata_store_config(
         db_path=(DISTRIBS_BASE_DIR / image_name / "kvstore.db").as_posix()
     )
 
+    store_ref = None
+    if persistence and persistence.stores:
+        store_ref = persistence.stores.metadata
+
     return resolve_backend(
         persistence=persistence,
-        store_ref=persistence.metadata if persistence else None,
+        store_ref=store_ref,
         default_factory=lambda: default_config,
         store_name="metadata",
     )
@@ -137,9 +141,13 @@ def resolve_conversations_store_config(
         db_path=(RUNTIME_BASE_DIR / "conversations.db").as_posix()
     )
 
+    store_ref = None
+    if persistence and persistence.stores:
+        store_ref = persistence.stores.conversations
+
     return resolve_backend(
         persistence=persistence,
-        store_ref=persistence.conversations if persistence else None,
+        store_ref=store_ref,
         default_factory=lambda: default_config,
         store_name="conversations",
     )