fix(build, imageSpec): keep essential werf-stage-content-digest label

Signed-off-by: Aleksei Igrychev <aleksei.igrychev@palark.com>

Author: alexey-igrychev

Diff for: pkg/build/build_phase.go

@@ -860,8 +860,6 @@ func (phase *BuildPhase) findAndFetchStageFromSecondaryStagesStorage(ctx context
 				contentDigest, exist := stageDescCopy.Info.Labels[imagePkg.WerfStageContentDigestLabel]
 				if exist {
 					stg.SetContentDigest(contentDigest)
-				} else if stg.Name() == stage.ImageSpec { // The content digest tag might be missing for the imageSpec stage (removed by the user).
-					stg.SetContentDigest(stageDescCopy.Info.GetDigest())
 				} else {
 					panic(fmt.Sprintf("expected stage %q content digest label to be set!", stg.Name()))
 				}
@@ -983,8 +981,6 @@ func (phase *BuildPhase) calculateStage(ctx context.Context, img *image.Image, s
 		contentDigest, exist := stageDesc.Info.Labels[imagePkg.WerfStageContentDigestLabel]
 		if exist {
 			stageContentSig = contentDigest
-		} else if stg.Name() == stage.ImageSpec { // The content digest tag might be missing for the imageSpec stage (removed by the user).
-			stageContentSig = stageDesc.Info.GetDigest()
 		} else {
 			panic(fmt.Sprintf("expected stage %q content digest label to be set!", stg.Name()))
 		}
@@ -1188,8 +1184,6 @@ func (phase *BuildPhase) atomicBuildStageImage(ctx context.Context, img *image.I
 			contentDigest, exist := stageDesc.Info.Labels[imagePkg.WerfStageContentDigestLabel]
 			if exist {
 				stg.SetContentDigest(contentDigest)
-			} else if stg.Name() == stage.ImageSpec { // The content digest tag might be missing for the imageSpec stage (removed by the user).
-				stg.SetContentDigest(stageDesc.Info.GetDigest())
 			} else {
 				panic(fmt.Sprintf("expected stage %q content digest label to be set!", stg.Name()))
 			}

Diff for: pkg/build/stage/image_spec.go

@@ -22,7 +22,7 @@ const (
 	labelTemplateImage      = "image"
 	labelTemplateProject    = "project"
 	labelTemplateDelimiter  = "%"
-	werfLabelsGlobalWarning = `The "werf" and "werf-parent-stage-id" labels cannot be removed within the imageSpec stage, as they are essential for the proper operation of host and container registry cleanup.
+	werfLabelsGlobalWarning = `The "werf", "werf-stage-content-digest" and "werf.io/parent-stage-id" labels cannot be removed within the imageSpec stage, as they are essential for the proper operation of host and container registry cleanup.
 
 If you need to remove all werf labels, use the werf export command. By default, this command removes all werf labels and fully detaches images from werf control, transferring host and container registry cleanup entirely to the user.
 
@@ -207,7 +207,7 @@ func (s *ImageSpecStage) modifyLabels(ctx context.Context, labels, addLabels map
 			continue
 		}
 
-		if key == image.WerfLabel || key == image.WerfParentStageID {
+		if key == image.WerfLabel || key == image.WerfParentStageID || key == image.WerfStageContentDigestLabel {
 			if !keepEssentialWerfLabels {
 				shouldPrintGlobalWarn = true
 			}