fix(private-org-sync): run source and destination ls-remote in parallel

Instead of querying source and destination branch heads sequentially,
run both ls-remote calls concurrently using goroutines. This saves one
network round-trip per repo.

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

Author: petr-muller

cmd/private-org-sync/main.go

@@ -712,7 +712,7 @@ func main() {
 			continue
 		}
 
-		// ls-remote destination once per repo
+		// ls-remote source and destination in parallel
 		destUrlRaw := fmt.Sprintf("%s/%s/%s", syncer.prefix, o.targetOrg, dstRepo)
 		destUrl, err := url.Parse(destUrlRaw)
 		if err != nil {
@@ -726,8 +726,27 @@ func main() {
 			destUrl.User = url.User(syncer.token)
 		}
 
-		dstHeads, err := getRemoteBranchHeads(repoLogger, syncer.git, gitDir, destUrl.String())
-		if err != nil {
+		srcRemote := fmt.Sprintf("%s-%s", key.org, key.repo)
+
+		type lsRemoteResult struct {
+			heads RemoteBranchHeads
+			err   error
+		}
+		dstResult := make(chan lsRemoteResult, 1)
+		srcResult := make(chan lsRemoteResult, 1)
+		go func() {
+			heads, err := getRemoteBranchHeads(repoLogger, syncer.git, gitDir, destUrl.String())
+			dstResult <- lsRemoteResult{heads, err}
+		}()
+		go func() {
+			heads, err := getRemoteBranchHeads(repoLogger, withRetryOnNonzero(syncer.git, 5), gitDir, srcRemote)
+			srcResult <- lsRemoteResult{heads, err}
+		}()
+
+		dst := <-dstResult
+		src := <-srcResult
+
+		if dst.err != nil {
 			message := "destination repository does not exist or we cannot access it"
 			if syncer.failOnNonexistentDst {
 				repoLogger.Errorf("%s", message)
@@ -740,17 +759,17 @@ func main() {
 			continue
 		}
 
-		// ls-remote source once per repo
-		srcRemote := fmt.Sprintf("%s-%s", key.org, key.repo)
-		srcHeads, err := getRemoteBranchHeads(repoLogger, withRetryOnNonzero(syncer.git, 5), gitDir, srcRemote)
-		if err != nil {
-			repoLogger.WithError(err).Error("Failed to determine branch HEADs in source")
+		if src.err != nil {
+			repoLogger.WithError(src.err).Error("Failed to determine branch HEADs in source")
 			for _, source := range branches {
 				errs = append(errs, fmt.Errorf("%s: failed to determine branch HEADs in source", source.String()))
 			}
 			continue
 		}
 
+		dstHeads := dst.heads
+		srcHeads := src.heads
+
 		for _, source := range branches {
 			syncer.logger = config.LoggerForInfo(config.Info{
 				Metadata: api.Metadata{