Clean up snapshot save command and plain sink

Fix AWS-only guard, align container lookup with aws.go patterns, remove the unused NewPlainSinkSplit constructor and its dead errOut routing, and minor code clarity improvements.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: anisaoshafi

cmd/snapshot.go

@@ -3,7 +3,6 @@ package cmd
 import (
 	"fmt"
 	"os"
-	"slices"
 	"time"
 
 	"github.com/localstack/lstk/internal/config"
@@ -57,29 +56,30 @@ Cloud destinations are not yet supported.`,
 				return fmt.Errorf("failed to get config: %w", err)
 			}
 
-			awsIdx := slices.IndexFunc(appConfig.Containers, func(c config.ContainerConfig) bool {
-				return c.Type == config.EmulatorAWS
-			})
-			if awsIdx < 0 && len(appConfig.Containers) > 0 {
+			awsContainer := config.ContainerConfig{Type: config.EmulatorAWS, Port: config.DefaultAWSPort}
+			var found bool
+			for _, c := range appConfig.Containers {
+				if c.Type == config.EmulatorAWS {
+					awsContainer = c
+					found = true
+					break
+				}
+			}
+			if !found {
 				return fmt.Errorf("snapshot is only supported for the AWS emulator")
 			}
 
 			rt, err := runtime.NewDockerRuntime(cfg.DockerHost)
 			if err != nil {
 				return err
 			}
-
-			awsContainer := config.ContainerConfig{Type: config.EmulatorAWS, Port: config.DefaultAWSPort}
-			if awsIdx >= 0 {
-				awsContainer = appConfig.Containers[awsIdx]
-			}
 			host, _ := endpoint.ResolveHost(cmd.Context(), awsContainer.Port, cfg.LocalStackHost)
 			exporter := aws.NewClient()
 
 			if isInteractiveMode(cfg) {
 				return ui.RunSnapshotSave(cmd.Context(), rt, []config.ContainerConfig{awsContainer}, exporter, host, dest)
 			}
-			return snapshot.Save(cmd.Context(), rt, []config.ContainerConfig{awsContainer}, exporter, host, dest, output.NewPlainSinkSplit(os.Stdout, os.Stderr))
+			return snapshot.Save(cmd.Context(), rt, []config.ContainerConfig{awsContainer}, exporter, host, dest, output.NewPlainSink(os.Stdout))
 		},
 	}
 }

internal/output/plain_sink.go

@@ -7,27 +7,15 @@ import (
 )
 
 type PlainSink struct {
-	out    io.Writer
-	errOut io.Writer
-	err    error
+	out io.Writer
+	err error
 }
 
 func NewPlainSink(out io.Writer) *PlainSink {
 	if out == nil {
 		out = os.Stdout
 	}
-	return &PlainSink{out: out, errOut: out}
-}
-
-// NewPlainSinkSplit creates a PlainSink that routes ErrorEvents to errOut and all others to out.
-func NewPlainSinkSplit(out, errOut io.Writer) *PlainSink {
-	if out == nil {
-		out = os.Stdout
-	}
-	if errOut == nil {
-		errOut = os.Stderr
-	}
-	return &PlainSink{out: out, errOut: errOut}
+	return &PlainSink{out: out}
 }
 
 // Err returns the first write error encountered, if any.
@@ -46,10 +34,6 @@ func (s *PlainSink) Emit(event Event) {
 	if !ok {
 		return
 	}
-	w := s.out
-	if _, isErr := event.(ErrorEvent); isErr {
-		w = s.errOut
-	}
-	_, err := fmt.Fprintln(w, line)
+	_, err := fmt.Fprintln(s.out, line)
 	s.setErr(err)
 }

internal/output/plain_sink_test.go

@@ -286,32 +286,6 @@ func TestPlainSink_TableWidth(t *testing.T) {
 	})
 }
 
-func TestPlainSinkSplit_RoutesErrorEventToErrOut(t *testing.T) {
-	var out, errOut bytes.Buffer
-	sink := NewPlainSinkSplit(&out, &errOut)
-
-	sink.Emit(ErrorEvent{Title: "Something failed"})
-
-	assert.Empty(t, out.String(), "ErrorEvent should not go to out")
-	assert.Contains(t, errOut.String(), "Something failed")
-}
-
-func TestPlainSinkSplit_RoutesOtherEventsToOut(t *testing.T) {
-	var out, errOut bytes.Buffer
-	sink := NewPlainSinkSplit(&out, &errOut)
-
-	sink.Emit(MessageEvent{Severity: SeverityInfo, Text: "hello"})
-
-	assert.Contains(t, out.String(), "hello")
-	assert.Empty(t, errOut.String(), "MessageEvent should not go to errOut")
-}
-
-func TestPlainSinkSplit_NilWritersFallback(t *testing.T) {
-	// nil writers should not panic (fallback to os.Stdout/os.Stderr)
-	sink := NewPlainSinkSplit(nil, nil)
-	assert.NotNil(t, sink)
-}
-
 func TestPlainSink_ErrReturnsNilOnSuccess(t *testing.T) {
 	var out bytes.Buffer
 	sink := NewPlainSink(&out)

internal/snapshot/destination.go

@@ -31,8 +31,8 @@ func ParseDestination(dest string, now time.Time) (string, error) {
 			strings.HasPrefix(lower, "cloud:"):
 			return "", ErrRemoteNotSupported
 		case strings.Contains(lower, "://"):
-			scheme := dest[:strings.Index(lower, "://")+3]
-			return "", fmt.Errorf("%w: %q", ErrUnknownScheme, scheme)
+			scheme, _, _ := strings.Cut(dest, "://")
+			return "", fmt.Errorf("%w: %q", ErrUnknownScheme, scheme+"://")
 		}
 	}
 

internal/snapshot/save.go

@@ -12,7 +12,6 @@ import (
 	"github.com/localstack/lstk/internal/runtime"
 )
 
-// Save exports the emulator's state via exporter and writes it to dest.
 func Save(ctx context.Context, rt runtime.Runtime, containers []config.ContainerConfig, exporter StateExporter, host, dest string, sink output.Sink) (retErr error) {
 	if err := rt.IsHealthy(ctx); err != nil {
 		rt.EmitUnhealthyError(sink, err)