refactor: Add ProviderContext for a flexible storage directory

- Introduce ProviderContext class to decouple provider storage paths from absolute paths
- Add storage_dir attribute to StackRunConfig to accept CLI options
- Implement storage directory resolution with prioritized fallbacks:
  1. CLI option (--state-directory)
  2. Environment variable (LLAMA_STACK_STATE_DIR)
  3. Default distribution directory
- Standardize provider signatures to follow context, config, deps pattern
- Update provider implementations to use the new context-based approach
- Add comprehensive tests to verify state directory resolution

llama_stack/distribution/resolver.py

@@ -5,6 +5,8 @@
 # the root directory of this source tree.
 import importlib
 import inspect
+import os
+from pathlib import Path
 from typing import Any
 
 from llama_stack.apis.agents import Agents
@@ -42,6 +44,7 @@ from llama_stack.providers.datatypes import (
     BenchmarksProtocolPrivate,
     DatasetsProtocolPrivate,
     ModelsProtocolPrivate,
+    ProviderContext,
     ProviderSpec,
     RemoteProviderConfig,
     RemoteProviderSpec,
@@ -334,7 +337,15 @@ async def instantiate_provider(
 
         config_type = instantiate_class_type(provider_spec.config_class)
         config = config_type(**provider.config)
-        args = [config, deps]
+        # Build ProviderContext for every provider
+        distro_name = (
+            dist_registry.run_config.image_name
+            if dist_registry and hasattr(dist_registry, "run_config")
+            else provider.spec.api.value
+        )
+        storage_dir = resolve_storage_dir(config, distro_name)
+        context = ProviderContext(storage_dir=storage_dir)
+        args = [context, config, deps]
 
     fn = getattr(module, method)
     impl = await fn(*args)
@@ -413,3 +424,31 @@ async def resolve_remote_stack_impls(
             )
 
     return impls
+
+
+def resolve_storage_dir(config, distro_name: str) -> Path:
+    """
+    Resolves the storage directory for a provider in the following order of precedence:
+    1. CLI option (config.storage_dir)
+    2. Environment variable (LLAMA_STACK_STORAGE_DIR)
+    3. Fallback to <DISTRIBS_BASE_DIR>/<distro_name>
+
+    Args:
+        config: Provider configuration object
+        distro_name: Distribution name used for the fallback path
+
+    Returns:
+        Path: Resolved storage directory path
+    """
+    # Import here to avoid circular imports
+    from llama_stack.distribution.utils.config_dirs import DISTRIBS_BASE_DIR
+
+    # 1. CLI option
+    storage_dir = getattr(config, "storage_dir", None)
+    # 2. Environment variable
+    if not storage_dir:
+        storage_dir = os.environ.get("LLAMA_STACK_STORAGE_DIR")
+    # 3. Fallback
+    if not storage_dir:
+        storage_dir = str(DISTRIBS_BASE_DIR / distro_name)
+    return Path(storage_dir)