Expose workflow.Cause to retrieve cancellation cause

Author: Copilot

workflow/context.go

@@ -43,6 +43,16 @@ func WithCancelCause(parent Context) (ctx Context, cancel CancelCauseFunc) {
 	return sync.WithCancelCause(parent)
 }
 
+// Cause returns a non-nil error explaining why c was canceled.
+// The first cancellation of c or one of its parents sets the cause.
+// If that cancellation happened via a call to CancelCauseFunc(err),
+// then [Cause] returns err.
+// Otherwise Cause(c) returns the same value as c.Err().
+// Cause returns nil if c has not been canceled yet.
+func Cause(c Context) error {
+	return sync.Cause(c)
+}
+
 // WithValue returns a copy of parent in which the value associated with key is
 // val.
 //

workflow/context_test.go

@@ -0,0 +1,21 @@
+package workflow
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/cschleiden/go-workflows/internal/sync"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCause(t *testing.T) {
+	myErr := errors.New("my cause")
+
+	ctx, cancel := WithCancelCause(sync.Background())
+	require.Nil(t, Cause(ctx))
+
+	cancel(myErr)
+
+	require.ErrorIs(t, ctx.Err(), Canceled)
+	require.Equal(t, myErr, Cause(ctx))
+}