fix(lifecycle): retain parent cancellation at every shutdown return

lifecycle/lifecycle.go

@@ -238,7 +238,7 @@ func (a *App) Run(parent context.Context) error {
 			if !ok {
 				signals = nil
 			} else if err := receiveSignal(sig); err != nil {
-				return a.result(err)
+				return a.result(parent, err)
 			}
 			continue
 		default:
@@ -246,7 +246,6 @@ func (a *App) Run(parent context.Context) error {
 
 		a.mu.Lock()
 		if !a.stopping && parent.Err() != nil {
-			a.errs = append(a.errs, parent.Err())
 			a.stopLocked()
 			parentDone = nil
 		}
@@ -288,7 +287,7 @@ func (a *App) Run(parent context.Context) error {
 
 		if stopping {
 			if err := shutdown.Err(); err != nil {
-				return a.result(err)
+				return a.result(parent, err)
 			}
 			if setupDone == nil && teardownDone == nil {
 				if teardownIndex >= 0 {
@@ -297,7 +296,7 @@ func (a *App) Run(parent context.Context) error {
 					teardownDone = result
 					go func() { result <- m.Teardown(shutdown) }()
 				} else if active == 0 {
-					return a.result(nil)
+					return a.result(parent, nil)
 				}
 			}
 		}
@@ -325,7 +324,6 @@ func (a *App) Run(parent context.Context) error {
 		case <-a.wake:
 		case <-parentDone:
 			a.mu.Lock()
-			a.errs = append(a.errs, parent.Err())
 			a.stopLocked()
 			a.mu.Unlock()
 			parentDone = nil
@@ -335,16 +333,17 @@ func (a *App) Run(parent context.Context) error {
 				continue
 			}
 			if err := receiveSignal(sig); err != nil {
-				return a.result(err)
+				return a.result(parent, err)
 			}
 		case <-deadline:
-			return a.result(context.DeadlineExceeded)
+			return a.result(parent, context.DeadlineExceeded)
 		}
 	}
 }
 
-func (a *App) result(extra error) error {
+func (a *App) result(parent context.Context, extra error) error {
 	a.mu.Lock()
 	defer a.mu.Unlock()
-	return errors.Join(append(a.errs, extra)...)
+	// invariant: every completion and abandonment retains parent cancellation exactly once.
+	return errors.Join(append(a.errs, parent.Err(), extra)...)
 }