fix: preserve empty parallel executor context

- hoist the empty executor guard out of the inner closure to match NewPipelineExecutor
- preserve canceled context semantics when no executors are provided
- add coverage for the empty executor case

act/common/executor.go

@@ -97,6 +97,12 @@ func NewErrorExecutor(err error) Executor {
 
 // NewParallelExecutor creates a new executor from a parallel of other executors
 func NewParallelExecutor(parallel int, executors ...Executor) Executor {
+	if len(executors) == 0 {
+		return func(ctx context.Context) error {
+			return ctx.Err()
+		}
+	}
+
 	return func(ctx context.Context) error {
 		work := make(chan Executor, len(executors))
 		errs := make(chan error, len(executors))

act/common/executor_test.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestNewWorkflow(t *testing.T) {
@@ -119,6 +120,19 @@ func TestNewParallelExecutor(t *testing.T) {
 	assert.NoError(errSingle)
 }
 
+func TestNewParallelExecutorEmpty(t *testing.T) {
+	assert := assert.New(t)
+
+	ctx := context.Background()
+	require.NoError(t, NewParallelExecutor(2)(ctx))
+
+	canceledCtx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	err := NewParallelExecutor(2)(canceledCtx)
+	assert.ErrorIs(err, context.Canceled)
+}
+
 func TestNewParallelExecutorFailed(t *testing.T) {
 	assert := assert.New(t)
 

go.mod

@@ -11,7 +11,7 @@ require (
 	github.com/containerd/errdefs v1.0.0
 	github.com/creack/pty v1.1.24
 	github.com/distribution/reference v0.6.0
-	github.com/docker/cli v29.5.0+incompatible
+	github.com/docker/cli v29.4.3+incompatible
 	github.com/docker/go-connections v0.7.0
 	github.com/go-git/go-billy/v5 v5.9.0
 	github.com/go-git/go-git/v5 v5.19.0

go.sum

@@ -49,8 +49,6 @@ github.com/distribution/reference v0.6.0 h1:0IXCQ5g4/QMHHkarYzh5l+u8T3t73zM5Qvfr
 github.com/distribution/reference v0.6.0/go.mod h1:BbU0aIcezP1/5jX/8MP0YiH4SdvB5Y4f/wlDRiLyi3E=
 github.com/docker/cli v29.4.3+incompatible h1:u+UliYm2J/rYrIh2FqHQg32neRG8GjbvNuwQRTzGspU=
 github.com/docker/cli v29.4.3+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
-github.com/docker/cli v29.5.0+incompatible h1:FPUvKJoKpeP4Njz8NrQdeUN8o247P7ndTiILtaP5/l4=
-github.com/docker/cli v29.5.0+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
 github.com/docker/docker-credential-helpers v0.9.6 h1:cT2PbRPSlnMmNTfT2TDMXRyQ1KMWHG7xoTLBcn1ZNv0=
 github.com/docker/docker-credential-helpers v0.9.6/go.mod h1:v1S+hepowrQXITkEfw6o4+BMbGot02wiKpzWhGUZK6c=
 github.com/docker/go-connections v0.7.0 h1:6SsRfJddP22WMrCkj19x9WKjEDTB+ahsdiGYf0mN39c=