🔌 fix: Shared MCP Server Connection Management (#9822)

- Fixed a bug in reinitMCPServer where a user connection was created for an app-level server whenever this server is reinitialized
- Made MCPManager.getUserConnection to return an error if the connection is app-level
- Add MCPManager.getConnection to return either an app connection or a user connection based on the serverName
- Made MCPManager.appConnections public to avoid unnecessary wrapper methods.

packages/api/src/mcp/UserConnectionManager.ts

@@ -4,6 +4,7 @@ import { MCPConnectionFactory } from '~/mcp/MCPConnectionFactory';
 import { MCPServersRegistry } from '~/mcp/MCPServersRegistry';
 import { MCPConnection } from './connection';
 import type * as t from './types';
+import { ConnectionsRepository } from '~/mcp/ConnectionsRepository';
 
 /**
  * Abstract base class for managing user-specific MCP connections with lifecycle management.
@@ -14,6 +15,9 @@ import type * as t from './types';
  */
 export abstract class UserConnectionManager {
   protected readonly serversRegistry: MCPServersRegistry;
+  // Connections shared by all users.
+  public appConnections: ConnectionsRepository | null = null;
+  // Connections per userId -> serverName -> connection
   protected userConnections: Map<string, Map<string, MCPConnection>> = new Map();
   /** Last activity timestamp for users (not per server) */
   protected userLastActivity: Map<string, number> = new Map();
@@ -60,6 +64,13 @@ export abstract class UserConnectionManager {
       throw new McpError(ErrorCode.InvalidRequest, `[MCP] User object missing id property`);
     }
 
+    if (this.appConnections!.has(serverName)) {
+      throw new McpError(
+        ErrorCode.InvalidRequest,
+        `[MCP][User: ${userId}] Trying to create user-specific connection for app-level server "${serverName}"`,
+      );
+    }
+
     const userServerMap = this.userConnections.get(userId);
     let connection = forceNew ? undefined : userServerMap?.get(serverName);
     const now = Date.now();