feat: get_vm_provider() factory keyed off agent_settings.vm_provider

Reads `agent_settings.vm_provider` and `agent_settings.<provider>` from
the loaded proxy config and builds the matching provider. Defaults to
`noop`. Unknown values raise `ValueError` listing the supported
providers so config typos surface fast.

Validation #1 (test_factory) covers this path. Validation #6 (provider
swap is config-only) is also exercised here.

LIT-2878

litellm/proxy/agent_session_endpoints/vm_providers/factory.py

@@ -0,0 +1,63 @@
+"""
+Factory for `AgentVMProvider` implementations.
+
+Reads `agent_settings.vm_provider` from the loaded proxy config. Default is
+`noop` so the proxy starts cleanly without AWS configured.
+
+Validation criterion #1 (`test_factory`) covers:
+- factory returns the right impl for each value
+- unknown values raise `ValueError`
+- defaults to `noop` when no config is set
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, Optional
+
+from litellm.proxy.agent_session_endpoints.vm_providers.base import AgentVMProvider
+from litellm.proxy.agent_session_endpoints.vm_providers.ec2 import EC2Provider
+from litellm.proxy.agent_session_endpoints.vm_providers.noop import NoopProvider
+
+# Registry of {name: factory_callable}. The factory takes the raw settings
+# dict (e.g. `agent_settings.ec2`) so per-provider config stays inside the
+# provider class, not the factory.
+_PROVIDER_REGISTRY = {
+    "noop": lambda settings: NoopProvider(),
+    "ec2": lambda settings: EC2Provider(settings=settings),
+}
+
+
+SUPPORTED_PROVIDERS = tuple(_PROVIDER_REGISTRY.keys())
+
+
+def get_vm_provider(
+    agent_settings: Optional[Dict[str, Any]] = None,
+) -> AgentVMProvider:
+    """
+    Build the configured provider.
+
+    `agent_settings` is the `agent_settings` block from `config.yaml`:
+
+    ```yaml
+    agent_settings:
+      vm_provider: ec2
+      ec2:
+        default_region: us-west-2
+        default_ami_id: ami-...
+        ...
+    ```
+
+    Defaults to `noop` if `agent_settings` is None or `vm_provider` is missing.
+    Raises `ValueError` for unknown provider names.
+    """
+    settings = agent_settings or {}
+    provider_name = settings.get("vm_provider", "noop")
+
+    if provider_name not in _PROVIDER_REGISTRY:
+        raise ValueError(
+            f"Unknown vm_provider {provider_name!r}. "
+            f"Supported: {', '.join(sorted(_PROVIDER_REGISTRY.keys()))}."
+        )
+
+    provider_settings = settings.get(provider_name, {}) or {}
+    return _PROVIDER_REGISTRY[provider_name](provider_settings)