test: stabilize json runtime captures (#52428) (thanks @karanuppal)

src/cli/mcp-cli.test.ts

@@ -15,6 +15,7 @@ vi.mock("../runtime.js", () => ({
   defaultRuntime: {
     log: (...args: unknown[]) => mockLog(...args),
     error: (...args: unknown[]) => mockError(...args),
+    writeStdout: (value: string) => mockLog(value.endsWith("\n") ? value.slice(0, -1) : value),
     writeJson: (value: unknown, space = 2) =>
       mockLog(JSON.stringify(value, null, space > 0 ? space : undefined)),
     exit: (code: number) => mockExit(code),