Fix idle timer review issues

internal/app/session.go

@@ -178,6 +178,11 @@ type SpawnSpec struct {
 	// or is closed. They must be attached before the PTY starts so a
 	// fast-exiting child cannot outrun cleanup registration.
 	CleanupPaths []string
+	// IdleDetection is the resolved per-preset idle classifier config.
+	// Must be installed before the child is published to s.children so
+	// the classifier goroutine never observes a nil/default config for
+	// a preset that overrides it.
+	IdleDetection *resolvedIdleDetection
 }
 
 // Spawn creates a new entry and starts its PTY. For Kind = command the
@@ -208,6 +213,12 @@ func (s *Session) Spawn(spec SpawnSpec, cols, rows uint16) (*Child, error) {
 	for _, path := range spec.CleanupPaths {
 		c.AddCleanupPath(path)
 	}
+	// Install idle-detection BEFORE publishing to s.children — otherwise
+	// the classifier goroutine could read c.idleDetection while the
+	// launcher is still racing to set it.
+	if spec.IdleDetection != nil {
+		c.setIdleDetection(spec.IdleDetection)
+	}
 	runID, err := c.startPTY(cols, rows)
 	if err != nil {
 		c.cleanupOwnedPaths()