fix(coderd/x/chatd): project memory extraction only creates memories

A question-only turn led the extractor to rewrite a correct memory with hallucinated content. Existing memories are now updated only by the main agent's tool or the UI; extraction proposals that collide with an existing name are dropped.
coder · f0ssel · Sep 11, 2026 · Sep 11, 2026 · Sep 11, 2026 · Sep 11, 2026
commit db834ae21a3a8f78f4706b364814520bef8c345c
diff --git a/coderd/x/chatd/projectmemory_extract.go b/coderd/x/chatd/projectmemory_extract.go
@@ -33,7 +33,7 @@ const projectMemoryExtractionPrompt = "You review a completed coding-chat turn a
 	chattool.ProjectMemoryGuidance + " " +
 	"Record only facts the user stated or explicitly confirmed in this turn. " +
 	"Never record that something is unknown, unspecified, undecided, or pending, and never record questions or the assistant's own guesses. " +
-	"Skip facts that already appear in the memory index unless the user changed them, and reuse the existing name when updating. " +
+	"Skip anything already covered by a memory in the index; existing memories are updated by the main agent, not by you. " +
 	"Most turns contain nothing new: return an empty list in that case."
 
 type projectMemoryExtraction struct {
@@ -141,21 +141,29 @@ func (p *Server) extractProjectMemories(ctx context.Context, logger slog.Logger,
 	}
 }
 
+// applyProjectMemoryUpsert records a memory the extractor proposed. It only
+// creates: dogfooding showed the extractor rewriting a correct memory with
+// hallucinated content after a question-only turn, so updates to existing
+// memories are reserved for the main agent's tool and the UI.
 func applyProjectMemoryUpsert(ctx context.Context, store database.Store, chat database.Chat, upsert projectMemoryExtractionUpsert) error {
 	normalized, err := normalizeProjectMemoryExtraction(upsert)
 	if err != nil {
 		return err
 	}
 	name, memoryType, description, body := normalized.Name, normalized.Type, normalized.Description, normalized.Body
 	_, existingErr := store.GetChatProjectMemoryByName(ctx, database.GetChatProjectMemoryByNameParams{ProjectID: chat.ProjectID.UUID, Name: name})
-	if existingErr != nil {
-		count, countErr := store.CountChatProjectMemoriesByProjectID(ctx, chat.ProjectID.UUID)
-		if countErr != nil {
-			return xerrors.Errorf("count project memories: %w", countErr)
-		}
-		if count >= chattool.MaxProjectMemories {
-			return xerrors.New("project memory limit reached")
-		}
+	if existingErr == nil {
+		return xerrors.Errorf("memory %q already exists", name)
+	}
+	if !errors.Is(existingErr, sql.ErrNoRows) {
+		return xerrors.Errorf("look up project memory: %w", existingErr)
+	}
+	count, countErr := store.CountChatProjectMemoriesByProjectID(ctx, chat.ProjectID.UUID)
+	if countErr != nil {
+		return xerrors.Errorf("count project memories: %w", countErr)
+	}
+	if count >= chattool.MaxProjectMemories {
+		return xerrors.New("project memory limit reached")
 	}
 	_, err = store.UpsertChatProjectMemoryByName(ctx, database.UpsertChatProjectMemoryByNameParams{
 		ProjectID: chat.ProjectID.UUID, OrganizationID: chat.OrganizationID, Type: memoryType,

diff --git a/coderd/x/chatd/projectmemory_extract_internal_test.go b/coderd/x/chatd/projectmemory_extract_internal_test.go
@@ -274,7 +274,8 @@ func TestExtractProjectMemories(t *testing.T) {
 			db.EXPECT().GetChatProjectMemoryByName(gomock.Any(), database.GetChatProjectMemoryByNameParams{
 				ProjectID: chat.ProjectID.UUID,
 				Name:      "release_notes",
-			}).Return(database.GetChatProjectMemoryByNameRow{}, nil),
+			}).Return(database.GetChatProjectMemoryByNameRow{}, sql.ErrNoRows),
+			db.EXPECT().CountChatProjectMemoriesByProjectID(gomock.Any(), chat.ProjectID.UUID).Return(int64(0), nil),
 			db.EXPECT().UpsertChatProjectMemoryByName(gomock.Any(), validUpsert).Return(database.ChatProjectMemory{}, nil),
 			db.EXPECT().UpsertChatProjectMemoryCursor(gomock.Any(), database.UpsertChatProjectMemoryCursorParams{
 				ChatID:         chat.ID,
@@ -290,6 +291,50 @@ func TestExtractProjectMemories(t *testing.T) {
 		require.NotContains(t, capturedPrompt, `"deletes"`)
 	})
 
+	t.Run("NeverOverwritesExistingMemory", func(t *testing.T) {
+		t.Parallel()
+
+		ctrl := gomock.NewController(t)
+		db := dbmock.NewMockStore(ctrl)
+		chat := newChat()
+		server := newServer(t, db, roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			response := objectResponse(t, map[string]any{
+				"upserts": []map[string]any{{
+					"name":        "release_notes",
+					"type":        database.ChatProjectMemoryTypeProject,
+					"description": "Hallucinated rewrite",
+					"body":        "Deploy day is Friday.",
+				}},
+			})
+			response.Request = req
+			return response, nil
+		}))
+		gomock.InOrder(
+			db.EXPECT().GetChatByID(gomock.Any(), chat.ID).Return(chat, nil),
+			db.EXPECT().GetChatProjectMemoryCursor(gomock.Any(), chat.ID).Return(
+				database.ChatProjectMemoryCursor{ChatID: chat.ID, HistoryVersion: 3}, nil,
+			),
+			db.EXPECT().GetChatMessagesForPromptByChatID(gomock.Any(), chat.ID).Return([]database.ChatMessage{
+				message(t, 1, database.ChatMessageRoleUser, "when do we deploy?", 5),
+			}, nil),
+			db.EXPECT().GetChatProjectMemoriesByProjectID(gomock.Any(), chat.ProjectID.UUID).Return(nil, nil),
+		)
+		expectModelResolution(db, chat)
+		gomock.InOrder(
+			db.EXPECT().GetChatProjectMemoryByName(gomock.Any(), database.GetChatProjectMemoryByNameParams{
+				ProjectID: chat.ProjectID.UUID,
+				Name:      "release_notes",
+			}).Return(database.GetChatProjectMemoryByNameRow{}, nil),
+			// No UpsertChatProjectMemoryByName: the existing memory is left alone.
+			db.EXPECT().UpsertChatProjectMemoryCursor(gomock.Any(), database.UpsertChatProjectMemoryCursorParams{
+				ChatID:         chat.ID,
+				HistoryVersion: chat.HistoryVersion,
+			}).Return(database.ChatProjectMemoryCursor{}, nil),
+		)
+
+		server.extractProjectMemories(t.Context(), slogtest.Make(t, nil), chat)
+	})
+
 	t.Run("RespectsCapForNewNames", func(t *testing.T) {
 		t.Parallel()