fix: add MCP server ready check to prevent initialization errors

Add server ready state tracking for MCP service to prevent
"Received request before initialization was complete" errors
when clients connect before GNS3 server completes startup.

Changes:
- Add MCP server ready state management with wait/notify mechanism
- Modify auth wrapper to wait for server initialization before accepting connections
- Set MCP server ready flag after GNS3 startup completes

This ensures MCP protocol initialization handshake only occurs
after GNS3 server is fully initialized, preventing race
conditions during server startup.

gns3server/api/routes/mcp/__init__.py

@@ -70,6 +70,65 @@ from .computes import (
 log = logging.getLogger(__name__)
 
 
+# ── Server ready state ────────────────────────────────────────────────
+# Tracks whether GNS3 server has completed initialization.
+# MCP connections are rejected until startup completes to prevent
+# "Received request before initialization was complete" errors.
+
+_mcp_server_ready = False
+_mcp_ready_lock = asyncio.Lock()
+
+
+def set_mcp_server_ready(ready: bool = True) -> None:
+    """
+    Set MCP server ready state.
+
+    Should be called after GNS3 startup completes (database, controller, etc.)
+    to allow MCP connections to proceed.
+
+    Args:
+        ready: True to mark server as ready, False to mark as not ready
+    """
+    global _mcp_server_ready
+    _mcp_server_ready = ready
+    if ready:
+        log.info("MCP server is now ready to accept connections")
+
+
+async def wait_for_mcp_ready() -> None:
+    """
+    Wait until MCP server is ready before accepting connections.
+
+    Returns immediately if already ready. Otherwise waits with a timeout
+    to prevent indefinite blocking during server startup issues.
+    """
+    global _mcp_server_ready
+    if _mcp_server_ready:
+        return
+
+    log.debug("MCP server not ready yet, waiting for initialization to complete...")
+
+    async with _mcp_ready_lock:
+        # Double-check after acquiring lock
+        if _mcp_server_ready:
+            return
+
+        # Wait with a timeout to prevent indefinite blocking
+        # Timeout: 5 seconds (50 * 0.1s)
+        for _ in range(50):
+            if _mcp_server_ready:
+                log.debug("MCP server is now ready, proceeding with connection")
+                return
+            await asyncio.sleep(0.1)
+
+        # Timeout reached - log warning but allow connection anyway
+        # This prevents complete deadlocks if startup has issues
+        log.warning(
+            "MCP server ready check timed out after 5 seconds, "
+            "allowing connection anyway (may experience errors)"
+        )
+
+
 # ── Per‑connection JWT token  ─────────────────────────────────────────
 # Set during SSE authentication, read by tool handlers running in the
 # same asyncio task (contextvars propagate through asyncio.to_thread).
@@ -459,6 +518,9 @@ def _make_auth_wrapper(inner_app):
     """
 
     async def auth_wrapper(scope, receive, send):
+        # Wait for GNS3 server to complete initialization before accepting MCP connections
+        await wait_for_mcp_ready()
+
         if scope["type"] == "http" and scope["method"] == "GET":
             token = None
             headers = dict(scope.get("headers", []))

gns3server/core/tasks.py

@@ -84,6 +84,11 @@ async def startup(app: FastAPI) -> None:
         m = module.instance()
         m.port_manager = PortManager.instance()
 
+    # Mark MCP server as ready to accept connections
+    from gns3server.api.routes.mcp import set_mcp_server_ready
+    set_mcp_server_ready(True)
+    log.info("GNS3 server startup completed")
+
 
 async def shutdown(app: FastAPI) -> None:
     """