[Question] Is _resolve_session_id expected to be called in STDIO mode?

Hi! First of all, thank you for this great project!

What I Noticed

While testing with fastmcp dev (STDIO mode), I found that after calling set_active_instance, subsequent tool calls experience a ~10 second delay before executing.

After digging into the code, I found that PluginHub._resolve_session_id() is being called even in STDIO mode. Since there's no WebSocket plugin connected in STDIO mode, it waits for the full retry timeout (40 × 250ms ≈ 10s) before falling back.

The good news: After the timeout, the tool call still succeeds via the "recently active instance" fallback mechanism. So functionality is not broken — it's just a delay on the first call after setting an active instance.

Steps to Reproduce

1. Start the MCP server using fastmcp dev to launch MCP Inspector
2. Open Unity Editor with a project that has MCP for Unity package installed
3. In MCP Inspector, call the set_active_instance tool to set an active Unity instance (e.g., MyProject@abc123)
4. Call any other tool (e.g., execute_menu_item, get_hierarchy, etc.)
5. Observe: The tool call hangs for ~10 seconds before executing

Code Analysis

In main.py, PluginHub.configure() is called unconditionally on startup:

# main.py lines 103-107
global _plugin_registry
if _plugin_registry is None:
    _plugin_registry = PluginRegistry()
    loop = asyncio.get_running_loop()
    PluginHub.configure(_plugin_registry, loop)  # Always called!

Then in unity_instance_middleware.py, the middleware checks PluginHub.is_configured() which is always True:

# unity_instance_middleware.py lines 84-93
async def on_call_tool(self, context: MiddlewareContext, call_next):
    ctx = context.fastmcp_context
    active_instance = self.get_active_instance(ctx)
    if active_instance:
        if PluginHub.is_configured():  # Always True!
            try:
                session_id = await PluginHub._resolve_session_id(active_instance)
            except Exception:
                self.clear_active_instance(ctx)
                return await call_next(context)

Questions

I'm not sure if this is intentional design or something that could be improved:

1. Is PluginHub intended to be configured/used in STDIO mode as well?
2. Should the middleware check the transport mode before calling _resolve_session_id?

Environment

• Server version: 8.1.4
• Transport mode: STDIO
• OS: Windows