fix(master): remember the tag's deployed digest after any tag job (#9)

Renames last_auto_digest to last_tag_digest. FinishJob sets it to the pinned
digest after any successful job whose to_ref had no digest, so a rollback
holds however the update was started.

internal/e2e/agent_master_test.go

@@ -91,14 +91,14 @@ func (m *memStore) SetPollError(_ context.Context, ids []int64, msg string) erro
 	return nil
 }
 
-func (m *memStore) SetLastAutoDigest(_ context.Context, id int64, digest string) error {
+func (m *memStore) SetLastTagDigest(_ context.Context, id int64, digest string) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	svc, ok := m.svcRows[id]
 	if !ok {
 		return model.ErrNotFound
 	}
-	svc.LastAutoDigest = digest
+	svc.LastTagDigest = digest
 	m.svcRows[id] = svc
 	return nil
 }
@@ -241,6 +241,9 @@ func (m *memStore) FinishJob(_ context.Context, agentID, jobID int64, f model.Jo
 	if f.Status == model.JobSucceeded {
 		svc := m.svcRows[j.ServiceID]
 		svc.DesiredRef = f.Ref
+		if _, d, _ := strings.Cut(f.Ref, "@"); !strings.Contains(requestedRef, "@") && d != "" {
+			svc.LastTagDigest = d
+		}
 		// Same rule as the SQL: the job was created for the suggested ref after it was reported.
 		requested, digest, _ := strings.Cut(requestedRef, "@")
 		if svc.AvailableAt != nil && svc.AvailableRef == requested && !svc.AvailableAt.After(j.CreatedAt) &&