fix(chat-ui): fix MCPEvent layering, batch localStorage writes, module-level test imports

- Move MCPEvent interface definition into chat/types.ts (single source of truth)
- MCPEventsDisplay.tsx now imports MCPEvent from types.ts instead of defining it locally
- Batch MCP event localStorage writes: accumulate during stream, persist once in finally
- Move test imports to module level per PEP 8 convention

tests/test_litellm/test_chat_ui_responses_session.py

@@ -6,11 +6,15 @@ Verifies that:
 2. Absence of previous_response_id does not break the call
 3. The aresponses function signature exposes the expected parameters
 """
+import inspect
+import json
 import os
 import sys
+import unittest.mock as mock
 
 sys.path.insert(0, os.path.abspath("../.."))
 
+import httpx
 import pytest
 
 import litellm
@@ -21,8 +25,6 @@ class TestResponsesSessionChaining:
 
     def test_responses_api_signature_accepts_previous_response_id(self):
         """aresponses must accept previous_response_id and onResponseId-like params."""
-        import inspect
-
         sig = inspect.signature(litellm.aresponses)
         assert "previous_response_id" in sig.parameters, (
             "aresponses must accept previous_response_id for multi-turn session chaining"
@@ -33,13 +35,9 @@ class TestResponsesSessionChaining:
     @pytest.mark.asyncio
     async def test_previous_response_id_included_in_request_body(self):
         """previous_response_id must appear in the outgoing HTTP request body."""
-        import httpx
-
         captured_body: dict = {}
 
         async def mock_send(self_transport, request: httpx.Request, **kwargs):
-            import json
-
             try:
                 captured_body.update(json.loads(request.content))
             except Exception:
@@ -68,8 +66,6 @@ class TestResponsesSessionChaining:
                 request=request,
             )
 
-        import unittest.mock as mock
-
         with mock.patch("httpx.AsyncClient.send", mock_send):
             try:
                 await litellm.aresponses(
@@ -88,13 +84,9 @@ class TestResponsesSessionChaining:
     @pytest.mark.asyncio
     async def test_no_previous_response_id_omitted_from_request(self):
         """When previous_response_id is None, it must not appear in the request body."""
-        import httpx
-
         captured_body: dict = {}
 
         async def mock_send(self_transport, request: httpx.Request, **kwargs):
-            import json
-
             try:
                 captured_body.update(json.loads(request.content))
             except Exception:
@@ -118,8 +110,6 @@ class TestResponsesSessionChaining:
             }
             return httpx.Response(200, json=response_json, request=request)
 
-        import unittest.mock as mock
-
         with mock.patch("httpx.AsyncClient.send", mock_send):
             try:
                 await litellm.aresponses(

ui/litellm-dashboard/src/components/chat/ChatPage.tsx

@@ -304,10 +304,9 @@ const ChatPage: React.FC<ChatPageProps> = ({ accessToken, userRole, userId, user
           previousResponseId,
           (id: string) => setResponsesSessionId(id),
           (event: MCPEvent) => {
+            // Accumulate locally only — persisted once in finally to avoid
+            // one full localStorage write per MCP event during streaming.
             accumulatedMCPEvents.push(event);
-            // Persist a snapshot to the assistant message so events survive
-            // across turns instead of disappearing when the next send starts.
-            updateLastAssistantMessage(convId!, { mcpEvents: [...accumulatedMCPEvents] });
           },
         );
       } catch (err: unknown) {
@@ -321,6 +320,10 @@ const ChatPage: React.FC<ChatPageProps> = ({ accessToken, userRole, userId, user
           });
         }
       } finally {
+        // Persist MCP events once after the turn ends (single localStorage write).
+        if (accumulatedMCPEvents.length > 0) {
+          updateLastAssistantMessage(convId!, { mcpEvents: accumulatedMCPEvents });
+        }
         setIsStreaming(false);
         abortControllerRef.current = null;
       }

ui/litellm-dashboard/src/components/chat/types.ts

@@ -1,6 +1,29 @@
-import type { MCPEvent } from "../playground/chat_ui/MCPEventsDisplay";
-
-export type { MCPEvent };
+/** Represents a single MCP tool event emitted during an assistant turn. */
+export interface MCPEvent {
+  type: string;
+  sequence_number?: number;
+  output_index?: number;
+  item_id?: string;
+  item?: {
+    id?: string;
+    type?: string;
+    server_label?: string;
+    tools?: Array<{
+      name: string;
+      description: string;
+      annotations?: {
+        read_only?: boolean;
+      };
+      input_schema?: unknown;
+    }>;
+    name?: string;
+    arguments?: string;
+    output?: string;
+  };
+  delta?: string;
+  arguments?: string;
+  timestamp?: number;
+}
 
 export interface ChatMessage {
   id: string;

ui/litellm-dashboard/src/components/playground/chat_ui/MCPEventsDisplay.tsx

@@ -1,35 +1,12 @@
 import React from "react";
 import { Typography, Collapse } from "antd";
+import type { MCPEvent } from "../../chat/types";
+
+export type { MCPEvent };
 
 const { Text } = Typography;
 const { Panel } = Collapse;
 
-export interface MCPEvent {
-  type: string;
-  sequence_number?: number;
-  output_index?: number;
-  item_id?: string;
-  item?: {
-    id?: string;
-    type?: string;
-    server_label?: string;
-    tools?: Array<{
-      name: string;
-      description: string;
-      annotations?: {
-        read_only?: boolean;
-      };
-      input_schema?: any;
-    }>;
-    name?: string;
-    arguments?: string;
-    output?: string;
-  };
-  delta?: string;
-  arguments?: string;
-  timestamp?: number;
-}
-
 interface MCPEventsDisplayProps {
   events: MCPEvent[];
   className?: string;