fix: stabilize gateway config tests + tool schema

src/gateway/server-methods/agent.ts

@@ -119,7 +119,7 @@ export const agentHandlers: GatewayRequestHandlers = {
           undefined,
           errorShape(
             ErrorCodes.INVALID_REQUEST,
-            `invalid agent params: unknown channel: ${normalized}`,
+            `invalid agent params: unknown channel: ${String(normalized)}`,
           ),
         );
         return;