fix(lifecycle): preserve mixed shutdown error identity

README.md

@@ -35,6 +35,11 @@ an injected signal cancels work before teardown. One shared shutdown deadline
 abandons shutdown. Callbacks must cooperate: abandonment cannot kill goroutines,
 and the caller owns process exit and any unreleased resources.
 
+During App-initiated shutdown, callback errors containing only the callback's
+context cancellation are omitted. Mixed cancellation and independent failures
+are retained intact to preserve wrapper types, identity and custom matching;
+these errors may still match cancellation through `errors.Is`.
+
 The caller owns signal subscription, SIGINT/SIGTERM filtering, a channel buffered
 for at least two signals, and subscription cleanup. Nil signals disable reception.
 There are no signal subscriptions, process exits, external dependencies or CLI

lifecycle/lifecycle.go

@@ -131,44 +131,32 @@ func (a *App) stopLocked() {
 	a.notifyLocked()
 }
 
-// remaining removes only cancellation leaves caused by established shutdown,
-// preserving independent components even inside a wrapped errors.Join.
-func remaining(err, cancellation error) (error, bool) {
+// cancellationOnly recognizes expected cancellation without rebuilding error trees.
+func cancellationOnly(err, cancellation error) bool {
 	if err == nil {
-		return nil, false
+		return false
 	}
 	if err == cancellation {
-		return nil, true
+		return true
 	}
 	if many, ok := err.(interface{ Unwrap() []error }); ok {
-		var kept []error
-		changed := false
-		for _, child := range many.Unwrap() {
-			e, removed := remaining(child, cancellation)
-			changed = changed || removed
-			if e != nil {
-				kept = append(kept, e)
+		children := many.Unwrap()
+		for _, child := range children {
+			if !cancellationOnly(child, cancellation) {
+				return false
 			}
 		}
-		if changed {
-			return errors.Join(kept...), true
-		}
+		return len(children) > 0
 	}
 	if one, ok := err.(interface{ Unwrap() error }); ok {
-		kept, changed := remaining(one.Unwrap(), cancellation)
-		if changed {
-			if kept == nil {
-				return nil, true
-			}
-			return fmt.Errorf("%s: %w", err.Error(), kept), true
-		}
+		return cancellationOnly(one.Unwrap(), cancellation)
 	}
-	return err, false
+	return false
 }
 
 func (a *App) recordLocked(ctx context.Context, phase, name string, err error) {
-	if a.stopping && context.Cause(ctx) == a.shutdownCause {
-		err, _ = remaining(err, ctx.Err())
+	if a.stopping && context.Cause(ctx) == a.shutdownCause && cancellationOnly(err, ctx.Err()) {
+		err = nil
 	}
 	if err != nil {
 		a.errs = append(a.errs, fmt.Errorf("%s %q: %w", phase, name, err))
@@ -196,7 +184,9 @@ func (a *App) launchLocked(ctx context.Context, phase, name string, fn func(cont
 // In-flight setup is awaited within that budget before rollback; abandoned setup
 // is never torn down later. Deadline or second signal abandons outstanding work.
 // Observed failures are joined; expected callback cancellation during established
-// shutdown is omitted, while initiating failures and every teardown error remain.
+// shutdown is omitted only for cancellation-only error trees. Mixed errors remain
+// intact to preserve wrapper types, identity and matching, so may still match
+// cancellation. Initiating failures and every teardown error remain.
 // Cancellation is omitted only when context.Cause proves App caused it; parent
 // propagation and independently canceled descendants are retained conservatively.
 // Run never recovers panics, closes Signals or exits the process.

lifecycle/lifecycle_test.go

@@ -541,7 +541,75 @@ func TestMixedShutdownErrorPreservesCause(t *testing.T) {
 	if !errors.As(err, &pathErr) || pathErr != independent || !errors.Is(err, io.ErrUnexpectedEOF) {
 		t.Fatalf("independent cause lost: %v", err)
 	}
-	if errors.Is(err, context.Canceled) {
-		t.Fatalf("expected cancellation retained: %v", err)
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("mixed wrapper was reconstructed: %v", err)
+	}
+}
+
+// matchingError exercises wrapper-owned matching independently of its child.
+type matchingError struct {
+	child error
+	match error
+}
+
+func (e *matchingError) Error() string        { return "custom: " + e.child.Error() }
+func (e *matchingError) Unwrap() error        { return e.child }
+func (e *matchingError) Is(target error) bool { return target == e.match }
+
+func TestMixedShutdownErrorPreservesWrapper(t *testing.T) {
+	for _, kind := range []string{"path", "custom"} {
+		t.Run(kind, func(t *testing.T) {
+			signals := make(chan os.Signal, 2)
+			a := newApp(t, signals, time.Second)
+			ready := make(chan struct{})
+			match := errors.New("custom match")
+			var original error
+			add(t, a, Module{Name: "mixed", Run: func(ctx context.Context) error {
+				close(ready)
+				<-ctx.Done()
+				joined := errors.Join(ctx.Err(), io.ErrUnexpectedEOF)
+				if kind == "path" {
+					original = &os.PathError{Op: "read", Path: "queue", Err: joined}
+				} else {
+					original = &matchingError{child: joined, match: match}
+				}
+				return original
+			}})
+			done := run(a, context.Background())
+			wait(t, ready)
+			signals <- syscall.SIGTERM
+			err := receive(t, done)
+			if !errors.Is(err, original) || !errors.Is(err, io.ErrUnexpectedEOF) {
+				t.Fatalf("wrapper identity or inner failure lost: %v", err)
+			}
+			if kind == "path" {
+				var pathErr *os.PathError
+				if !errors.As(err, &pathErr) || pathErr != original {
+					t.Fatalf("typed wrapper lost: %v", err)
+				}
+			} else {
+				var custom *matchingError
+				if !errors.As(err, &custom) || custom != original || !errors.Is(err, match) {
+					t.Fatalf("custom matching lost: %v", err)
+				}
+			}
+		})
+	}
+}
+
+func TestCancellationOnly(t *testing.T) {
+	for _, err := range []error{
+		context.Canceled,
+		fmt.Errorf("wrapped: %w", context.Canceled),
+		&os.PathError{Op: "read", Path: "queue", Err: errors.Join(context.Canceled, fmt.Errorf("wrapped: %w", context.Canceled))},
+	} {
+		if !cancellationOnly(err, context.Canceled) {
+			t.Errorf("expected cancellation not recognized: %v", err)
+		}
+	}
+	for _, err := range []error{nil, io.ErrUnexpectedEOF, context.DeadlineExceeded, errors.Join(context.Canceled, io.ErrUnexpectedEOF)} {
+		if cancellationOnly(err, context.Canceled) {
+			t.Errorf("independent error classified as cancellation: %v", err)
+		}
 	}
 }