diff --git a/internal/llmadapters/pi_rpc_extension_unix_test.go b/internal/llmadapters/pi_rpc_extension_unix_test.go
index e2f21b37..8395ba81 100644
--- a/internal/llmadapters/pi_rpc_extension_unix_test.go
+++ b/internal/llmadapters/pi_rpc_extension_unix_test.go
@@ -26,16 +26,25 @@ func TestPiRPCReviewerHelperStaysInParentProcessGroup(t *testing.T) {
 		t.Fatalf("WriteFile(helper): %v", err)
 	}
 	extensionPath := filepath.Join(tempDir, "extension.mjs")
-	extension := piRPCReviewerExtension(helperPath, filepath.Join(tempDir, "config.json"), tempDir, 2048, 5*time.Second, "")
+	const helperTimeout = 5 * time.Second
+	extension := piRPCReviewerExtension(helperPath, filepath.Join(tempDir, "config.json"), tempDir, 2048, helperTimeout, "")
 	if err := os.WriteFile(extensionPath, []byte(extension), 0o600); err != nil { // #nosec G703 -- extensionPath is rooted in t.TempDir.
 		t.Fatalf("WriteFile(extension): %v", err)
 	}
 	runnerPath := filepath.Join(tempDir, "runner.mjs")
-	runner := "import extension from " + strconv.Quote(extensionPath) + ";\nconst tools = {};\nextension({ registerTool(tool) { tools[tool.name] = tool; } });\nvoid tools.cr_diff.execute('call-1', {}, new AbortController().signal);\n"
+	runner := "import extension from " + strconv.Quote(extensionPath) + ";\nconst tools = {};\nextension({ registerTool(tool) { tools[tool.name] = tool; } });\nvoid tools.cr_diff.execute('call-1', {}, new AbortController().signal).then(result => { if (result.isError) { console.error(JSON.stringify(result)); process.exitCode = 1; } });\n"
 	if err := os.WriteFile(runnerPath, []byte(runner), 0o600); err != nil {
 		t.Fatalf("WriteFile(runner): %v", err)
 	}
 	cmd := exec.Command(nodePath, runnerPath) // #nosec G204 -- test launches the discovered Node executable with a test-owned script.
+	outputPath := filepath.Join(tempDir, "runner.log")
+	output, err := os.Create(outputPath) // #nosec G304 -- outputPath is rooted in t.TempDir.
+	if err != nil {
+		t.Fatalf("Create(runner log): %v", err)
+	}
+	defer func() { _ = output.Close() }()
+	cmd.Stdout = output
+	cmd.Stderr = output
 	cmd.Dir = tempDir
 	cmd.Env = append(os.Environ(), "PI_RPC_TEST_PID="+pidPath)
 	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
@@ -45,10 +54,24 @@ func TestPiRPCReviewerHelperStaysInParentProcessGroup(t *testing.T) {
 	defer func() {
 		_ = syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
 		_ = cmd.Wait()
+		if t.Failed() {
+			data, err := os.ReadFile(outputPath) // #nosec G304 -- outputPath is rooted in t.TempDir.
+			if err != nil {
+				t.Logf("ReadFile(runner log): %v", err)
+			} else {
+				t.Logf("runner output: %s", data)
+			}
+		}
 	}()
-	eventually(t, 3*time.Second, func() bool {
-		_, err := os.Stat(pidPath)
-		return err == nil
+	// Runner startup precedes the helper's own timeout; allow both stages rather
+	// than treating a slow Node startup as a process-group cleanup failure.
+	eventually(t, 2*helperTimeout, func() bool {
+		data, err := os.ReadFile(pidPath) // #nosec G304 -- pidPath is rooted in t.TempDir.
+		if err != nil {
+			return false
+		}
+		pid, err := strconv.Atoi(strings.TrimSpace(string(data)))
+		return err == nil && pid > 0
 	})
 	pidData, err := os.ReadFile(pidPath) // #nosec G304 -- pidPath is rooted in t.TempDir.
 	if err != nil {
@@ -59,6 +82,13 @@ func TestPiRPCReviewerHelperStaysInParentProcessGroup(t *testing.T) {
 		t.Fatalf("Atoi(pid): %v", err)
 	}
 	t.Cleanup(func() { _ = syscall.Kill(helperPID, syscall.SIGKILL) })
+	helperGroup, err := syscall.Getpgid(helperPID)
+	if err != nil {
+		t.Fatalf("Getpgid(helper): %v", err)
+	}
+	if helperGroup != cmd.Process.Pid {
+		t.Fatalf("helper process group = %d, want runner group %d", helperGroup, cmd.Process.Pid)
+	}
 
 	if err := syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL); err != nil {
 		t.Fatalf("kill runner process group: %v", err)
diff --git a/internal/llmadapters/testdata/pi_rpc_detached_helper.cjs b/internal/llmadapters/testdata/pi_rpc_detached_helper.cjs
new file mode 100644
index 00000000..3559f8ed
--- /dev/null
+++ b/internal/llmadapters/testdata/pi_rpc_detached_helper.cjs
@@ -0,0 +1,8 @@
+// Negative control: deliberately violate the helper process-group contract.
+if (process.argv[1]?.endsWith('/runner.mjs')) {
+  const childProcess = require('node:child_process');
+  const originalSpawn = childProcess.spawn;
+  childProcess.spawn = (executable, args, options) =>
+    originalSpawn(executable, args, { ...options, detached: true });
+  require('node:module').syncBuiltinESMExports();
+}
diff --git a/internal/llmadapters/testdata/pi_rpc_slow_start.cjs b/internal/llmadapters/testdata/pi_rpc_slow_start.cjs
new file mode 100644
index 00000000..d29bc2c3
--- /dev/null
+++ b/internal/llmadapters/testdata/pi_rpc_slow_start.cjs
@@ -0,0 +1,4 @@
+// Delay only the process-group test's runner, not its helper.
+if (process.argv[1]?.endsWith('/runner.mjs')) {
+  Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0, 3100);
+}