address review feedback on cache and session store

management/server/auth/session.go

@@ -42,7 +42,7 @@ func (s *SessionStore) RegisterToken(ctx context.Context, token string, expiresA
 	key := usedTokenKeyPrefix + hashToken(token)
 	created, err := s.cache.SetNX(ctx, key, usedTokenMarker, ttl)
 	if err != nil {
-		return fmt.Errorf("failed to store used token entry: %w", err)
+		return fmt.Errorf("store used token entry: %w", err)
 	}
 	if !created {
 		return ErrTokenAlreadyUsed

management/server/auth/session_test.go

@@ -64,12 +64,12 @@ func TestSessionStore_ConcurrentRegistrationAllowsOneCaller(t *testing.T) {
 		case errors.Is(err, ErrTokenAlreadyUsed):
 			alreadyUsed++
 		default:
-			require.NoError(t, err)
+			require.NoError(t, err, "concurrent registration returned an unexpected error")
 		}
 	}
 
-	assert.Equal(t, 1, succeeded)
-	assert.Equal(t, attempts-1, alreadyUsed)
+	assert.Equal(t, 1, succeeded, "exactly one concurrent caller should register the token")
+	assert.Equal(t, attempts-1, alreadyUsed, "every other caller should be rejected as already used")
 }
 
 func TestSessionStore_RegisterDifferentTokensAreIndependent(t *testing.T) {
@@ -119,8 +119,8 @@ func TestSessionStore_CacheErrorIsReturned(t *testing.T) {
 	s := NewSessionStore(failingTokenCache{err: cacheErr})
 
 	err := s.RegisterToken(context.Background(), "token", time.Now().Add(time.Hour))
-	require.Error(t, err)
-	assert.ErrorIs(t, err, cacheErr)
+	require.Error(t, err, "cache failure should be surfaced to the caller")
+	assert.ErrorIs(t, err, cacheErr, "cache error should be wrapped, not replaced")
 }
 
 func TestHashToken_StableAndDoesNotLeak(t *testing.T) {

management/server/cache/memory.go

@@ -33,6 +33,12 @@ func (s *goCacheStore) SetNX(_ context.Context, key, value string, ttl time.Dura
 	return true, nil
 }
 
+// GetDel reads the value under key and removes it. go-cache has no native read-and-delete
+// and releases its own lock between the two calls, so mu holds the pair together and no
+// value is consumed twice.
+//
+// Writes do not take mu: a Set landing mid-pair is lost, since GetDel returns the prior
+// value and deletes the new one. Callers must write a consumed key only once.
 func (s *goCacheStore) GetDel(_ context.Context, key string) (string, bool, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()