fix(srv/stream): properly remove sessionTool to prevent memory leak (#365)

Author: cryo-zd

server/streamable_http.go

@@ -465,7 +465,7 @@ func (s *StreamableHTTPServer) handleDelete(w http.ResponseWriter, r *http.Reque
 	}
 
 	// remove the session relateddata from the sessionToolsStore
-	s.sessionTools.set(sessionID, nil)
+	s.sessionTools.delete(sessionID)
 
 	// remove current session's requstID information
 	s.sessionRequestIDs.Delete(sessionID)
@@ -533,6 +533,12 @@ func (s *sessionToolsStore) set(sessionID string, tools map[string]ServerTool) {
 	s.tools[sessionID] = tools
 }
 
+func (s *sessionToolsStore) delete(sessionID string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	delete(s.tools, sessionID)
+}
+
 // streamableHttpSession is a session for streamable-http transport
 // When in POST handlers(request/notification), it's ephemeral, and only exists in the life of the request handler.
 // When in GET handlers(listening), it's a real session, and will be registered in the MCP server.