coder · ibetitsmike · Aug 24, 2026 · Aug 24, 2026 · Aug 24, 2026 · Aug 24, 2026
diff --git a/coderd/apidoc/docs.go b/coderd/apidoc/docs.go
diff --git a/coderd/apidoc/swagger.json b/coderd/apidoc/swagger.json
diff --git a/coderd/exp_chats.go b/coderd/exp_chats.go
@@ -1102,6 +1102,42 @@ func validateChatMCPServerIDs(
 	return unique, invalid, nil
 }
 
+// normalizeRequestedChatMCPServerIDs validates a request's MCP server
+// selection for an existing chat. When requested is nil there is no
+// change to make. IDs already persisted on the chat are exempt from the
+// enabled-in-organization check: a server that is disabled or revoked
+// after selection must not block sends. The generation path skips
+// servers the chat can no longer use, and keeping the ID preserves the
+// selection if the server is re-enabled. A non-nil response indicates
+// the caller must write it with the returned status and stop.
+func (api *API) normalizeRequestedChatMCPServerIDs(ctx context.Context, chat database.Chat, requested *[]uuid.UUID) (*[]uuid.UUID, int, *codersdk.Response) {
+	if requested == nil {
+		return nil, 0, nil
+	}
+	normalized, invalid, err := validateChatMCPServerIDs(ctx, api.Database, chat.OrganizationID, *requested)
+	if err != nil {
+		return nil, http.StatusInternalServerError, &codersdk.Response{
+			Message: "Failed to validate MCP server IDs.",
+			Detail:  err.Error(),
+		}
+	}
+	persisted := make(map[uuid.UUID]struct{}, len(chat.MCPServerIDs))
+	for _, id := range chat.MCPServerIDs {
+		persisted[id] = struct{}{}
+	}
+	newlyInvalid := make([]uuid.UUID, 0, len(invalid))
+	for _, id := range invalid {
+		if _, ok := persisted[id]; !ok {
+			newlyInvalid = append(newlyInvalid, id)
+		}
+	}
+	if len(newlyInvalid) > 0 {
+		resp := invalidChatMCPServerIDsResponse(newlyInvalid)
+		return nil, http.StatusBadRequest, &resp
+	}
+	return &normalized, 0, nil
+}
+
 func invalidChatMCPServerIDsResponse(ids []uuid.UUID) codersdk.Response {
 	invalid := make([]string, 0, len(ids))
 	for _, id := range ids {
@@ -2555,36 +2591,12 @@ func (api *API) postChatMessages(rw http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if req.MCPServerIDs != nil {
-		normalizedMCPServerIDs, invalidMCPServerIDs, err := validateChatMCPServerIDs(ctx, api.Database, chat.OrganizationID, *req.MCPServerIDs)
-		if err != nil {
-			httpapi.Write(ctx, rw, http.StatusInternalServerError, codersdk.Response{
-				Message: "Failed to validate MCP server IDs.",
-				Detail:  err.Error(),
-			})
-			return
-		}
-		req.MCPServerIDs = &normalizedMCPServerIDs
-		// IDs already persisted on the chat are exempt: a server that
-		// is disabled or revoked after selection must not block sends.
-		// The generation path skips servers the chat can no longer use,
-		// and keeping the ID preserves the selection if the server is
-		// re-enabled.
-		persisted := make(map[uuid.UUID]struct{}, len(chat.MCPServerIDs))
-		for _, id := range chat.MCPServerIDs {
-			persisted[id] = struct{}{}
-		}
-		newlyInvalid := make([]uuid.UUID, 0, len(invalidMCPServerIDs))
-		for _, id := range invalidMCPServerIDs {
-			if _, ok := persisted[id]; !ok {
-				newlyInvalid = append(newlyInvalid, id)
-			}
-		}
-		if len(newlyInvalid) > 0 {
-			httpapi.Write(ctx, rw, http.StatusBadRequest, invalidChatMCPServerIDsResponse(newlyInvalid))
-			return
-		}
+	normalizedMCPServerIDs, status, mcpResp := api.normalizeRequestedChatMCPServerIDs(ctx, chat, req.MCPServerIDs)
+	if mcpResp != nil {
+		httpapi.Write(ctx, rw, status, *mcpResp)
+		return
 	}
+	req.MCPServerIDs = normalizedMCPServerIDs
 
 	if req.PlanMode != nil {
 		if !validateChatPlanMode(*req.PlanMode) {
@@ -2803,13 +2815,20 @@ func (api *API) patchChatMessage(rw http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	editMCPServerIDs, status, mcpResp := api.normalizeRequestedChatMCPServerIDs(ctx, chat, req.MCPServerIDs)
+	if mcpResp != nil {
+		httpapi.Write(ctx, rw, status, *mcpResp)
+		return
+	}
+
 	editResult, editErr := api.chatDaemon.EditMessage(ctx, chatd.EditMessageOptions{
 		ChatID:          chat.ID,
 		CreatedBy:       apiKey.UserID,
 		EditedMessageID: messageID,
 		Content:         contentBlocks,
 		ModelConfigID:   editModelConfigID,
 		ReasoningEffort: editReasoningEffort,
+		MCPServerIDs:    editMCPServerIDs,
 	})
 	if editErr != nil {
 		if writeChatHookErr(ctx, rw, editErr, "Chat message denied by lifecycle hook.") {

diff --git a/coderd/exp_chats_test.go b/coderd/exp_chats_test.go
@@ -9942,6 +9942,98 @@ func TestPatchChatMessage(t *testing.T) {
 		require.False(t, foundOriginalInChat)
 	})
 
+	t.Run("MCPServerIDsApplied", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+		client, db := newChatClientWithDatabase(t)
+		firstUser := coderdtest.CreateFirstUser(t, client.Client)
+		_ = createChatModel(t, client)
+
+		orgConfig := dbgen.MCPServerConfig(t, db, database.MCPServerConfig{
+			OrganizationID: firstUser.OrganizationID,
+			Enabled:        true,
+		})
+
+		chat, err := client.CreateChat(ctx, codersdk.CreateChatRequest{
+			OrganizationID: firstUser.OrganizationID,
+			Content: []codersdk.ChatInputPart{{
+				Type: codersdk.ChatInputPartTypeText,
+				Text: "before mcp edit",
+			}},
+		})
+		require.NoError(t, err)
+		require.Empty(t, chat.MCPServerIDs)
+
+		messagesResult, err := client.GetChatMessages(ctx, chat.ID, nil)
+		require.NoError(t, err)
+		userMessageID := messagesResult.Messages[0].ID
+
+		edited, err := client.EditChatMessage(ctx, chat.ID, userMessageID, codersdk.EditChatMessageRequest{
+			Content: []codersdk.ChatInputPart{{
+				Type: codersdk.ChatInputPartTypeText,
+				Text: "edit enabling the mcp server",
+			}},
+			MCPServerIDs: &[]uuid.UUID{orgConfig.ID},
+		})
+		require.NoError(t, err)
+
+		storedChat, err := db.GetChatByID(dbauthz.AsSystemRestricted(ctx), chat.ID)
+		require.NoError(t, err)
+		require.Equal(t, []uuid.UUID{orgConfig.ID}, storedChat.MCPServerIDs)
+
+		// Omitting the field preserves the persisted selection.
+		_, err = client.EditChatMessage(ctx, chat.ID, edited.Message.ID, codersdk.EditChatMessageRequest{
+			Content: []codersdk.ChatInputPart{{
+				Type: codersdk.ChatInputPartTypeText,
+				Text: "edit without an mcp selection",
+			}},
+		})
+		require.NoError(t, err)
+
+		storedChat, err = db.GetChatByID(dbauthz.AsSystemRestricted(ctx), chat.ID)
+		require.NoError(t, err)
+		require.Equal(t, []uuid.UUID{orgConfig.ID}, storedChat.MCPServerIDs)
+	})
+
+	t.Run("MCPServerIDsInvalidRejected", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+		client, db := newChatClientWithDatabase(t)
+		firstUser := coderdtest.CreateFirstUser(t, client.Client)
+		_ = createChatModel(t, client)
+
+		chat, err := client.CreateChat(ctx, codersdk.CreateChatRequest{
+			OrganizationID: firstUser.OrganizationID,
+			Content: []codersdk.ChatInputPart{{
+				Type: codersdk.ChatInputPartTypeText,
+				Text: "before invalid mcp edit",
+			}},
+		})
+		require.NoError(t, err)
+
+		messagesResult, err := client.GetChatMessages(ctx, chat.ID, nil)
+		require.NoError(t, err)
+		userMessageID := messagesResult.Messages[0].ID
+
+		unknownID := uuid.New()
+		_, err = client.EditChatMessage(ctx, chat.ID, userMessageID, codersdk.EditChatMessageRequest{
+			Content: []codersdk.ChatInputPart{{
+				Type: codersdk.ChatInputPartTypeText,
+				Text: "edit selecting an unknown mcp server",
+			}},
+			MCPServerIDs: &[]uuid.UUID{unknownID},
+		})
+		sdkErr := requireSDKError(t, err, http.StatusBadRequest)
+		require.Equal(t, "One or more MCP server IDs are invalid or disabled.", sdkErr.Message)
+		require.Equal(t, "Invalid IDs: "+unknownID.String(), sdkErr.Detail)
+
+		storedChat, err := db.GetChatByID(dbauthz.AsSystemRestricted(ctx), chat.ID)
+		require.NoError(t, err)
+		require.Empty(t, storedChat.MCPServerIDs)
+	})
+
 	t.Run("CrossOrgModelConfigRejected", func(t *testing.T) {
 		t.Parallel()
 

diff --git a/coderd/x/chatd/chatd.go b/coderd/x/chatd/chatd.go
@@ -1173,6 +1173,10 @@ type EditMessageOptions struct {
 	// original message's model is preserved.
 	ModelConfigID   uuid.UUID
 	ReasoningEffort *string
+	// MCPServerIDs, when non-nil, replaces the chat's MCP server
+	// selection before the replacement turn runs. When nil the
+	// current selection is preserved.
+	MCPServerIDs *[]uuid.UUID
 }
 
 // EditMessageResult contains the replacement user message and chat status.
@@ -1243,6 +1247,36 @@ func enforceForcedMCPServerIDs(ctx context.Context, store database.Store, organi
 	return merged, nil
 }
 
+// applyRequestedMCPServerIDs replaces the chat's MCP server selection
+// inside the state-machine transaction when a request provides one.
+// Explore child chats keep the spawn-time snapshot immutable. Force On
+// MCP servers are enforced server-side so a caller cannot remove them
+// by tampering with the update (Cure53 CDM-02-010).
+func (p *Server) applyRequestedMCPServerIDs(ctx context.Context, store database.Store, lockedChat database.Chat, requested *[]uuid.UUID) (database.Chat, error) {
+	if requested == nil {
+		return lockedChat, nil
+	}
+	if isExploreSubagentMode(lockedChat.Mode) {
+		p.logger.Warn(ctx,
+			"ignoring explore subagent mcp server ids update, snapshot is immutable after spawn",
+			slog.F("chat_id", lockedChat.ID),
+		)
+		return lockedChat, nil
+	}
+	enforcedIDs, err := enforceForcedMCPServerIDs(ctx, store, lockedChat.OrganizationID, lockedChat.OwnerID, *requested)
+	if err != nil {
+		return database.Chat{}, err
+	}
+	updated, err := store.UpdateChatMCPServerIDs(ctx, database.UpdateChatMCPServerIDsParams{
+		ID:           lockedChat.ID,
+		MCPServerIDs: enforcedIDs,
+	})
+	if err != nil {
+		return database.Chat{}, xerrors.Errorf("update chat mcp server ids: %w", err)
+	}
+	return updated, nil
+}
+
 // CreateChat creates a chat with its initial history through
 // chatstate.CreateChat. The new chat starts in `running` status per
 // the chat execution state model. Ownership hints wake chat workers.
@@ -1514,30 +1548,9 @@ func (p *Server) SendMessage(
 			return err
 		}
 
-		// Update MCP server IDs on the chat when explicitly provided.
-		// Explore child chats keep the spawn-time snapshot immutable.
-		if requestedMCPServerIDs != nil {
-			if isExploreSubagentMode(lockedChat.Mode) {
-				p.logger.Warn(ctx,
-					"ignoring explore subagent mcp server ids update, snapshot is immutable after spawn",
-					slog.F("chat_id", opts.ChatID),
-				)
-			} else {
-				// Force On MCP servers are enforced server-side so a
-				// caller cannot remove them by tampering with the
-				// update (Cure53 CDM-02-010).
-				enforcedIDs, enforceErr := enforceForcedMCPServerIDs(ctx, store, lockedChat.OrganizationID, lockedChat.OwnerID, *requestedMCPServerIDs)
-				if enforceErr != nil {
-					return enforceErr
-				}
-				lockedChat, err = store.UpdateChatMCPServerIDs(ctx, database.UpdateChatMCPServerIDsParams{
-					ID:           opts.ChatID,
-					MCPServerIDs: enforcedIDs,
-				})
-				if err != nil {
-					return xerrors.Errorf("update chat mcp server ids: %w", err)
-				}
-			}
+		lockedChat, err = p.applyRequestedMCPServerIDs(ctx, store, lockedChat, requestedMCPServerIDs)
+		if err != nil {
+			return err
 		}
 
 		messageCreatedBy := opts.CreatedBy
@@ -1885,6 +1898,11 @@ func (p *Server) EditMessage(
 		}
 		editedMsg = target
 
+		lockedChat, err = p.applyRequestedMCPServerIDs(ctx, store, lockedChat, opts.MCPServerIDs)
+		if err != nil {
+			return err
+		}
+
 		modelOverride, err := validateModelConfigOverride(ctx, store, lockedChat.OrganizationID, opts.ModelConfigID)
 		if err != nil {
 			return err