feat: NoopProvider for tests + agent_settings.vm_provider=noop config

In-memory `AgentVMProvider` used by the unit tests and as the default when
`agent_settings.vm_provider` is unset. The factory returns `NoopProvider`
when no AWS-backed provider is configured so the proxy boots cleanly without
AWS credentials.

LIT-2878

litellm/proxy/agent_session_endpoints/vm_providers/noop.py

@@ -0,0 +1,49 @@
+"""
+No-op `AgentVMProvider` implementation.
+
+Used in tests and for environments without an EC2 backend. `provision` returns
+a fake handle immediately; `status` always reports `running`. The provider is
+the default in `factory.py` so the proxy starts up without AWS configured.
+"""
+
+from __future__ import annotations
+
+import uuid
+
+from litellm.proxy.agent_session_endpoints.vm_providers.base import (
+    AgentVMProvider,
+    ProvisionContext,
+    VMHandle,
+    VMState,
+    VMStatus,
+)
+
+
+class NoopProvider(AgentVMProvider):
+    """In-memory provider used by tests and `vm_provider: noop` config."""
+
+    name = "noop"
+
+    def __init__(self) -> None:
+        self._terminated: set = set()
+
+    async def provision(self, ctx: ProvisionContext) -> VMHandle:
+        vm_id = f"noop-{uuid.uuid4().hex[:12]}"
+        return VMHandle(
+            vm_id=vm_id,
+            provider=self.name,
+            region=(ctx.ec2_config.region if ctx.ec2_config else None),
+            metadata={
+                "session_id": ctx.session_id,
+                "team_id": ctx.team_id,
+                "mode": ctx.mode,
+            },
+        )
+
+    async def terminate(self, vm: VMHandle) -> None:
+        self._terminated.add(vm.vm_id)
+
+    async def status(self, vm: VMHandle) -> VMStatus:
+        if vm.vm_id in self._terminated:
+            return VMStatus(state=VMState.TERMINATED)
+        return VMStatus(state=VMState.RUNNING, public_ip="127.0.0.1")