fix: fix errors during repeated pull and rm operations; add tag validation on pull to ensure idempotency.

[PikaByter]

related issue：#483

FIx:
add tag validation when pulling

Test:

make build
chmod +x ./output/modctl
cd output
./modctl pull <image>
./modctl rmi <image>
./modctl pulll <image>
./modctl rmi <image>

[gemini-code-assist]

Code Review

This pull request introduces a StatTag method to the Storage interface and its distribution implementation to verify tag existence. This new method is utilized in the pullIfNotExist function to ensure manifests are pushed when a tag is missing, even if the underlying blob is already present. The changes also include minor formatting adjustments to model file constants and updated mocks. A review comment suggested using errors.As for more robust error handling of wrapped ErrTagUnknown errors.

[gemini-code-assist]

Using switch err.(type) to check for distribution.ErrTagUnknown may fail if the error is wrapped. Since the project uses wrapped errors (e.g., %w), it is safer and more idiomatic to use errors.As to check for specific error types.

Suggested change

	if err != nil {
	switch err.(type) {
	case distribution.ErrTagUnknown:
	return false, nil
	}
	return false, err
	}
	if err != nil {
	var tagErr distribution.ErrTagUnknown
	if errors.As(err, &tagErr) {
	return false, nil
	}
	return false, err
	}

[aftersnow]

(duplicate, please see the English review below)

[aftersnow]

Thanks for the contribution! The fix direction is correct. A few suggestions:

Required

1. Missing digest validation on tag re-creation path: When manifest exists but tag doesn't, io.ReadAll(reader) reads content and pushes it, but the function returns early before validateDigest(). Please add validation or comment why it's safe to skip.

2. No unit test coverage: The core new path (StatManifest=true, StatTag=false) has no tests. Please add coverage.

Suggestions

3. The formatting changes in constants.go are unrelated to the fix — consider a separate commit.

4. The second commit message feat: update dis is unclear — please reword it.