objectpool: Cast transaction vote when repository already linked

If a repository is already linked to the object pool, cast a vote to
ensure that repository state is consistent among replicas.

internal/git/objectpool/link.go

@@ -2,6 +2,7 @@ package objectpool
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -11,6 +12,7 @@ import (
 	"gitlab.com/gitlab-org/gitaly/v16/internal/git/localrepo"
 	"gitlab.com/gitlab-org/gitaly/v16/internal/gitaly/transaction"
 	"gitlab.com/gitlab-org/gitaly/v16/internal/safe"
+	"gitlab.com/gitlab-org/gitaly/v16/internal/transaction/voting"
 )
 
 // Link will link the given repository to the object pool. This is done by writing the object pool's
@@ -33,6 +35,12 @@ func (o *ObjectPool) Link(ctx context.Context, repo *localrepo.Repo) (returnedEr
 	}
 
 	if linked {
+		// When the repository is already linked to the repository, cast a vote to ensure the
+		// repository is consistent with the other replicas.
+		if err := transaction.VoteOnContext(ctx, o.txManager, voting.VoteFromData([]byte("repository linked")), voting.Committed); err != nil {
+			return fmt.Errorf("vote on linked repository: %w", err)
+		}
+
 		return nil
 	}
 
@@ -148,7 +156,7 @@ func (o *ObjectPool) LinkedToRepository(repo *localrepo.Repo) (bool, error) {
 
 	relPath, err := getAlternateObjectDir(repo)
 	if err != nil {
-		if err == ErrAlternateObjectDirNotExist {
+		if errors.Is(err, ErrAlternateObjectDirNotExist) {
 			return false, nil
 		}
 		return false, err

internal/git/objectpool/link_test.go

@@ -182,6 +182,32 @@ func TestLink(t *testing.T) {
 				}
 			},
 		},
+		{
+			desc: "transactional repository already linked",
+			setup: func(t *testing.T, ctx context.Context) setupData {
+				cfg, pool, repo := setupObjectPool(t, ctx)
+
+				// Inject transaction manager to record transactions.
+				txManager := transaction.NewTrackingManager()
+				pool.txManager = txManager
+
+				// When transactions are enabled, a vote is cast if the repository is already linked
+				// to the same object pool.
+				altPath, err := repo.InfoAlternatesPath()
+				require.NoError(t, err)
+				require.NoError(t, os.WriteFile(altPath, []byte(getRelAltPath(t, repo, pool.Repo)), perm.SharedFile))
+
+				return setupData{
+					cfg:       cfg,
+					repo:      repo,
+					pool:      pool,
+					txManager: txManager,
+					expectedVotes: []transaction.PhasedVote{
+						{Vote: voting.VoteFromData([]byte("repository linked")), Phase: voting.Committed},
+					},
+				}
+			},
+		},
 		{
 			desc: "repository link transaction fails",
 			setup: func(t *testing.T, ctx context.Context) setupData {