Merge upstream/experimental into feat/citations

Resolved conflicts:
- backend/src/gateway/routers/artifacts.py: Keep citations block removal for markdown downloads
- frontend/src/components/workspace/messages/message-list-item.tsx: Keep improved citation handling with rehypePlugins, humanMessagePlugins, and CitationsLoadingIndicator

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/core/threads/hooks.ts

@@ -135,6 +135,7 @@ export function useSubmitThread({
           threadId: isNewThread ? threadId! : undefined,
           streamSubgraphs: true,
           streamResumable: true,
+          streamMode: ["values", "messages-tuple", "custom"],
           config: {
             recursion_limit: 1000,
           },

frontend/src/core/threads/types.ts

@@ -17,4 +17,5 @@ export interface AgentThreadContext extends Record<string, unknown> {
   model_name: string | undefined;
   thinking_enabled: boolean;
   is_plan_mode: boolean;
+  subagent_enabled: boolean;
 }