Fix idle timer review issues

internal/app/session_test.go

@@ -57,6 +57,50 @@ func TestParentExitKillsDescendants(t *testing.T) {
 	waitUntilNotLive(t, grandchild)
 }
 
+// TestSpawnInstallsIdleDetectionBeforePublish guarantees that a child
+// spawned with SpawnSpec.IdleDetection has its resolved config visible
+// the instant the child appears in s.children — closing the race where
+// the classifier could read c.idleDetection before the launcher set it.
+func TestSpawnInstallsIdleDetectionBeforePublish(t *testing.T) {
+	sess := NewSession(t.TempDir(), "test")
+	want := &resolvedIdleDetection{
+		strategy:        StrategyOSCTitleStability,
+		idleThresholdMS: 9999,
+	}
+	c, err := sess.Spawn(SpawnSpec{
+		Kind:          KindCommand,
+		Argv:          []string{"sh", "-c", "sleep 30"},
+		IdleDetection: want,
+	}, 80, 24)
+	if err != nil {
+		t.Fatalf("spawn: %v", err)
+	}
+	defer func() { _ = c.signal(syscall.SIGTERM) }()
+
+	// Read back via the same access path the classifier uses
+	// (sess.Children) so the test fails if the field is set only
+	// AFTER the child is published.
+	var found *Child
+	for _, ch := range sess.Children() {
+		if ch.ID == c.ID {
+			found = ch
+			break
+		}
+	}
+	if found == nil {
+		t.Fatalf("spawned child %s not in Children()", c.ID)
+	}
+	if found.idleDetection == nil {
+		t.Fatalf("idleDetection nil after Spawn returned")
+	}
+	if found.idleDetection.strategy != StrategyOSCTitleStability {
+		t.Fatalf("strategy: got %q want %q", found.idleDetection.strategy, StrategyOSCTitleStability)
+	}
+	if found.idleDetection.idleThresholdMS != 9999 {
+		t.Fatalf("threshold: got %d want 9999", found.idleDetection.idleThresholdMS)
+	}
+}
+
 func waitUntilLive(t *testing.T, c *Child) {
 	t.Helper()
 	deadline := time.Now().Add(5 * time.Second)