fix: suppress execution output on stdout

packages/engine/src/logger.test.ts

@@ -27,10 +27,11 @@ describe("createLogger", () => {
     errorSpy.mockRestore();
   });
 
-  it("formats log output as [prefix] message", () => {
+  it("formats log output as [prefix] message on stderr", () => {
     const logger = createLogger("test");
     logger.log("hello world");
-    expect(logSpy).toHaveBeenCalledWith("[test] hello world");
+    expect(logSpy).not.toHaveBeenCalled();
+    expect(errorSpy).toHaveBeenCalledWith("[test] hello world");
   });
 
   it("formats warn output as [prefix] message", () => {
@@ -52,36 +53,36 @@ describe("createLogger", () => {
     expect(errorSpy).toHaveBeenCalledWith("[test] failed:", err);
   });
 
-  it("delegates log to console.log, warn to console.warn, error to console.error", () => {
+  it("keeps log output off stdout", () => {
     const logger = createLogger("x");
     logger.log("a");
     logger.warn("b");
     logger.error("c");
-    expect(logSpy).toHaveBeenCalledTimes(1);
+    expect(logSpy).not.toHaveBeenCalled();
     expect(warnSpy).toHaveBeenCalledTimes(1);
-    expect(errorSpy).toHaveBeenCalledTimes(1);
+    expect(errorSpy).toHaveBeenCalledTimes(2);
   });
 
   it("pre-built instances use correct prefixes", () => {
     schedulerLog.log("tick");
-    expect(logSpy).toHaveBeenCalledWith("[scheduler] tick");
+    expect(errorSpy).toHaveBeenCalledWith("[scheduler] tick");
 
     executorLog.log("run");
-    expect(logSpy).toHaveBeenCalledWith("[executor] run");
+    expect(errorSpy).toHaveBeenCalledWith("[executor] run");
 
     triageLog.log("spec");
-    expect(logSpy).toHaveBeenCalledWith("[triage] spec");
+    expect(errorSpy).toHaveBeenCalledWith("[triage] spec");
 
     mergerLog.log("merge");
-    expect(logSpy).toHaveBeenCalledWith("[merger] merge");
+    expect(errorSpy).toHaveBeenCalledWith("[merger] merge");
 
     worktreePoolLog.log("prune");
-    expect(logSpy).toHaveBeenCalledWith("[worktree-pool] prune");
+    expect(errorSpy).toHaveBeenCalledWith("[worktree-pool] prune");
 
     reviewerLog.log("review");
-    expect(logSpy).toHaveBeenCalledWith("[reviewer] review");
+    expect(errorSpy).toHaveBeenCalledWith("[reviewer] review");
 
     remoteNodeLog.log("stream");
-    expect(logSpy).toHaveBeenCalledWith("[remote-node] stream");
+    expect(errorSpy).toHaveBeenCalledWith("[remote-node] stream");
   });
 });