feat(managed_agents): expose Agent/Session/Run/runtimes/sandboxes from package root

The package __init__ now re-exports the public surface so SDK callers
can do a single 'from litellm.managed_agents import Agent, Session, ...'
instead of digging into submodules.

Also pins what's public — anything not in __all__ is implementation
detail and may move.

litellm/managed_agents/__init__.py

@@ -0,0 +1,69 @@
+"""
+``litellm.managed_agents`` — Python SDK for spawning and driving managed agents.
+
+Public surface:
+
+  * ``Agent``                — handle for one ``LiteLLM_Agent`` row;
+                               spawns sessions.
+  * ``Session``              — one running session; ``send(prompt)``
+                               drives the runtime and yields events.
+  * ``Run``                  — read-only view of one ``LiteLLM_AgentRun``
+                               row; ``stream(starting_seq=N)`` replays
+                               persisted events.
+  * ``Event``                — the dataclass yielded by both runtimes
+                               and ``Run.stream``.
+  * ``AgentRuntime`` (+ subclasses ``ClaudeSDKAgentRuntime``,
+    ``LiteLLMAgentRuntime``) — the LLM tool-loop driver. Subclass to
+    add ``before_tool_call`` / ``after_tool_call`` hooks.
+  * ``Sandbox`` (+ subclasses ``LocalSandbox``, ``EC2SandboxViaSSM``)
+    — where tool calls actually execute.
+
+Typical use::
+
+    from litellm.managed_agents import (
+        Agent, LiteLLMAgentRuntime, LocalSandbox,
+    )
+
+    agent = await Agent.from_db_row(
+        row, db=prisma_client.db,
+        runtime=LiteLLMAgentRuntime(),
+        sandbox=LocalSandbox(),
+    )
+    session = await agent.create_session()
+    async for event in session.send("hello"):
+        print(event.type, event.data)
+"""
+
+from litellm.managed_agents.agent import Agent
+from litellm.managed_agents.agent_runtime import (
+    AgentConfig,
+    AgentRuntime,
+    ClaudeSDKAgentRuntime,
+    LiteLLMAgentRuntime,
+    SessionState,
+)
+from litellm.managed_agents.events import Event
+from litellm.managed_agents.run import Run
+from litellm.managed_agents.sandbox import (
+    EC2SandboxViaSSM,
+    LocalSandbox,
+    Sandbox,
+    ToolResult,
+)
+from litellm.managed_agents.session import Session
+
+__all__ = [
+    "Agent",
+    "Session",
+    "Run",
+    "Event",
+    "AgentRuntime",
+    "AgentConfig",
+    "SessionState",
+    "ClaudeSDKAgentRuntime",
+    "LiteLLMAgentRuntime",
+    "Sandbox",
+    "ToolResult",
+    "LocalSandbox",
+    "EC2SandboxViaSSM",
+]