Supported endpoints:
/websocket: WebSocket upgrade for CLI
/:userId/proxy/:agentId: A2A agent card (GET) or JSON-RPC (POST)
/:userId/graphql/:agentId: GraphQL over registered RESTful services (GET/POST)
/:userId/graphql/sdl: User-level GraphQL SDL (GET, optional repeated agentId query params)
/:userId/graphql/:agentId/sdl: Single-agent GraphQL SDL (GET)
/:userId/graphql/cache/clear: Clear cached GraphQL schemas for the user (POST)