fix(migrations): wait out GitHub rate limits and tolerate failed patch downloads (#40012)

Large GitHub migrations failed once the API budget ran out. A rejected
request never updated the downloader's rate state, so go-github refused
every retry locally.

- Record the rate limit from error responses too, so the next request
waits for the reset
- Retry repository-wide comment pages like the other downloader calls
- Stop `waitAndPickClient` spinning when the rate refresh fails
- Skip reaction requests when the reaction rollup reports none
- Log a failed patch download instead of failing the migration

---------

Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>

modules/migration/retry_downloader.go

@@ -154,6 +154,21 @@ func (d *RetryDownloader) GetComments(ctx context.Context, commentable Commentab
 	return comments, isEnd, err
 }
 
+func (d *RetryDownloader) GetAllComments(ctx context.Context, page, perPage int) ([]*Comment, bool, error) {
+	var (
+		comments []*Comment
+		isEnd    bool
+		err      error
+	)
+
+	err = d.retry(ctx, func(ctx context.Context) error {
+		comments, isEnd, err = d.Downloader.GetAllComments(ctx, page, perPage)
+		return err
+	})
+
+	return comments, isEnd, err
+}
+
 // GetPullRequests returns a repository's pull requests with retry
 func (d *RetryDownloader) GetPullRequests(ctx context.Context, page, perPage int) ([]*PullRequest, bool, error) {
 	var (

modules/migration/retry_downloader_test.go

@@ -11,12 +11,19 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestRetryDownloaderExhaustsAttempts(t *testing.T) {
-	failure := errors.New("permission denied")
-	attempts := 0
-	assert.ErrorIs(t, NewRetryDownloader(nil, 3, 0).retry(t.Context(), func(_ctx context.Context) error {
-		attempts++
-		return failure
-	}), failure)
-	assert.Equal(t, 3, attempts)
+type failingCommentsDownloader struct {
+	NullDownloader
+	attempts int
+}
+
+func (d *failingCommentsDownloader) GetAllComments(_ctx context.Context, _page, _perPage int) ([]*Comment, bool, error) {
+	d.attempts++
+	return nil, false, errors.New("permission denied")
+}
+
+func TestRetryDownloaderExhaustsAttempts(t *testing.T) {
+	source := &failingCommentsDownloader{}
+	_, _, err := NewRetryDownloader(source, 3, 0).GetAllComments(t.Context(), 1, 50)
+	assert.EqualError(t, err, "permission denied")
+	assert.Equal(t, 3, source.attempts)
 }