fix(responses-api): use server_name for MCP URL routing, fix test path

- Use server_name (not alias) as the URL path segment for MCP server_url;
  alias is a display name that may differ from the registered proxy route.
  URL-encode the path to handle names with spaces/special characters.
- Fix sys.path.insert in tests to use __file__-relative path so tests pass
  regardless of which directory pytest is invoked from.

tests/test_litellm/test_chat_ui_responses_session.py

@@ -12,7 +12,8 @@ import os
 import sys
 import unittest.mock as mock
 
-sys.path.insert(0, os.path.abspath("../.."))
+# Use __file__ so the import path is correct regardless of the pytest working directory.
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", ".."))
 
 import httpx
 import pytest

ui/litellm-dashboard/src/components/playground/llm_calls/responses_api.tsx

@@ -105,13 +105,16 @@ export async function makeOpenAIResponsesRequest(
         // Individual servers selected - create one entry per server
         selectedMCPServers.forEach((serverId) => {
           const server = mcpServers?.find((s) => s.server_id === serverId);
-          const serverName = server?.alias || server?.server_name || serverId;
+          // Use server_name for URL routing (proxy registers by name, not alias).
+          const routeName = server?.server_name || serverId;
+          // Use alias as the human-readable label when available.
+          const serverLabel = server?.alias || routeName;
           const allowedTools = mcpServerToolRestrictions?.[serverId] || [];
 
           tools.push({
             type: "mcp",
-            server_label: serverName, // unique label per server so tool calls route correctly
-            server_url: `${proxyBaseUrl}/mcp/${serverName}`,
+            server_label: serverLabel, // unique human-readable label per server
+            server_url: `${proxyBaseUrl}/mcp/${encodeURIComponent(routeName)}`,
             require_approval: "never",
             ...(allowedTools.length > 0 ? { allowed_tools: allowedTools } : {}),
           });