[Bug] Support async graph factories in AgentSeek API runtime

[kic635]

Summary

agentseek-api dev cannot load a graph manifest whose graph entry is an async factory. This blocks templates migrated from the LangGraph CLI when their graph must asynchronously initialize resources such as MCP clients and discovered tools.

Reproduction

A generated deepagents/mcp project declares a graph entry like:

{
  "graphs": {
    "mcp": "./src/agentseek_e2e_deepagents_mcp/agent.py:make_graph"
  }
}

The factory is asynchronous:

async def make_graph() -> CompiledStateGraph:
    # connect to stdio and Streamable HTTP MCP servers,
    # discover tools, then build the deep agent
    ...

Start the project with agentseek dev (which launches uv run agentseek-api dev). The HTTP service and /health endpoint start successfully. On the first /runs/stream request, graph loading fails with:

GraphManifestError: Graph definition did not resolve to a compiled graph or compilable StateGraph.

Why this happens

The graph loader invokes the configured factory and immediately coerces the return value to a compiled graph or StateGraph. For an async factory, the immediate return value is a coroutine. Because the loader does not detect and await awaitable results, it validates the coroutine object instead of the graph it produces.

This is specifically a LangGraph CLI to AgentSeek API runtime migration issue: the same template can be served by the previous runtime, but fails when its lifecycle is changed to agentseek-api dev.

Impact

• The service can pass health checks while every first graph execution fails.
• MCP tool discovery cannot be performed during async graph construction.
• Async database or remote-resource initialization has the same risk.
• doctor --live cannot detect the failure because it only checks HTTP readiness.

Proposed fix

In the graph loading path:

1. Invoke the configured graph factory.
2. Detect inspect.isawaitable(result).
3. Await the result in the async loading path.
4. Validate and compile the resolved StateGraph/compiled graph.
5. Preserve checkpointer and store arguments.
6. Keep the original factory exception as the error cause/context.

Regression coverage

Please add tests for:

• synchronous StateGraph factory;
• synchronous compiled graph factory;
• asynchronous StateGraph factory;
• asynchronous compiled graph factory;
• async factory exceptions;
• async factory with checkpointer/store arguments;
• a rendered MCP template loading its graph;
• /runs/stream successfully invoking an MCP calculator tool.

Acceptance criteria

After the fix, agentseek-api dev followed by the first /runs/stream request must load the async MCP graph successfully, emit stream events, and allow multiple turns on the same thread.