fix(assemble): an existing box is not an error, it should be simpl skipped

Signed-off-by: Luca Di Maio <luca.dimaio1@gmail.com>

pkg/commands/assemble.go

@@ -2,6 +2,7 @@ package commands
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"regexp"
 	"slices"
@@ -163,6 +164,12 @@ func (ac *AssembleCommand) createItem(ctx context.Context, item manifest.Item, d
 	}
 	_, err := createCmd.Execute(ctx, opts)
 	if err != nil {
+		var alreadyExists *ContainerAlreadyExistsError
+		if errors.As(err, &alreadyExists) {
+			ac.progress.Done()
+			ac.printer.Println("%s already exists", item.Name)
+			return nil
+		}
 		ac.progress.Fail()
 		return err
 	}

pkg/commands/assemble_test.go

@@ -29,6 +29,19 @@ func getEnterOptions(spy testutil.ContainerManagerSpy, index int) containermanag
 	return spy.Enter[index][0].(containermanager.EnterOptions)
 }
 
+func TestAssembleCommand_CreateSkipsExistingBox(t *testing.T) {
+	mock := &testutil.MockContainerManager{
+		ExistsFn: func(string) bool { return true },
+	}
+	cmd := newTestAssembleCommand(mock)
+
+	err := cmd.Execute(context.Background(), commands.AssembleOptions{
+		Items: []manifest.Item{{Name: "existing", Image: "alpine:3.21"}},
+	})
+	require.NoError(t, err, "an already-existing box must be skipped, not an error")
+	assert.Empty(t, mock.Spy.Remove, "skipping an existing box must not trigger cleanup")
+}
+
 func TestAssembleCommand_SetupBox_StartNowTrue(t *testing.T) {
 	mock := &testutil.MockContainerManager{}
 	cmd := newTestAssembleCommand(mock)