fix(master): seed the tag digest from running services and hide registry error text (#9)

internal/master/store/services.go

@@ -261,12 +261,13 @@ func (s *Store) SetPollError(ctx context.Context, ids []int64, msg string) error
 	return nil
 }
 
-// SetLastTagDigest records the digest of the followed tag that the poller
-// started an update for; see model.Service.LastTagDigest. Inventory writes never change it.
+// SetLastTagDigest sets last_tag_digest; see model.Service.LastTagDigest. The
+// poller calls it, and FinishJob sets the same column after a tag job.
+// Inventory writes never change it.
 func (s *Store) SetLastTagDigest(ctx context.Context, id int64, digest string) error {
 	if _, err := s.pool.Exec(ctx,
 		`UPDATE services SET last_tag_digest = $2 WHERE id = $1`, id, digest); err != nil {
-		return fmt.Errorf("set last auto digest: %w", err)
+		return fmt.Errorf("set last tag digest: %w", err)
 	}
 	return nil
 }