add try-extend variant

README.md

@@ -3,6 +3,7 @@
 Component identity propagation for layered Go libraries.
 
 Source: https://git.wisehodl.dev/jay/go-mana-component
+
 Mirror: https://github.com/wisehodl/go-mana-component
 
 ## What this library does
@@ -75,12 +76,14 @@ At the connection layer, another `MustExtend` call extends the path to
 
 ### Usage Notes
 
-**Error-Returning vs Panic Variants**:
+**Function Variants**:
 
 - Use `New` and `Extend` when a missing or invalid component is a recoverable
 condition.
 - Use `MustNew` and `MustExtend` at library boundaries where a missing
 component is a programming error that should halt execution immediately.
+- Use `TryExtend` if you only want to extend a component if it exists,
+otherwise use the parent context as-is.
 
 **Generic Output**:
 

c2p

@@ -0,0 +1 @@
+code2prompt -c -e go.sum -e bump.sh -e c2p

main.go

@@ -93,6 +93,21 @@ func Extend(ctx context.Context, name string) (context.Context, error) {
 	return insert(ctx, c.Module(), name, c.Path()), nil
 }
 
+// TryExtend returns ctx if no parent component is attached, otherwise
+// extends the existing component path.
+func TryExtend(ctx context.Context, name string) (context.Context, error) {
+	if ctx == nil {
+		return nil, fmt.Errorf("context is nil")
+	}
+
+	c, ok := Get(ctx)
+	if !ok || name == "" {
+		return ctx, nil
+	}
+
+	return insert(ctx, c.Module(), name, c.Path()), nil
+}
+
 // MustNew is New but panics on error.
 func MustNew(ctx context.Context, module string, name string) context.Context {
 	if ctx == nil {

main_test.go

@@ -80,6 +80,17 @@ func TestExtend(t *testing.T) {
 		}
 	})
 
+	t.Run("try passes through", func(t *testing.T) {
+		inCtx := context.Background()
+		outCtx, err := TryExtend(inCtx, "subcomponent")
+		if err != nil {
+			t.Fatal("unexpected error:", err)
+		}
+		if outCtx != inCtx {
+			t.Errorf("expected context to pass through")
+		}
+	})
+
 	t.Run("must variant should panic", func(t *testing.T) {
 		assertPanics(t, func() {
 			MustExtend(context.Background(), "subcomponent")