Fix: UserFillUp interactive forms not working in agent explore mode (#14589)

## Summary

- **Backend**: `_iter_session_completion_events` in `agent_api.py` was
filtering out `user_inputs` and `workflow_finished` SSE events, causing
agents with UserFillUp components to silently fail in explore mode — the
interactive form never appeared, while the same agent worked correctly
in run (editor) mode.
- **Frontend**: `SessionChat` component in explore mode was missing
`DebugContent` children rendering inside `MessageItem`, so even if the
backend forwarded the events, the form UI would not render. Added
`DebugContent`, `MarkdownContent`, `useAwaitCompentData` hook, and
input-disabling logic to match the run mode's `chat/box.tsx` behavior.

## What was changed

### Backend (`api/apps/restful_apis/agent_api.py`)
- Line 266: Added `"user_inputs"` and `"workflow_finished"` to the
allowed event filter in `_iter_session_completion_events`

### Frontend (`web/src/pages/agent/explore/components/session-chat.tsx`)
- Added imports: `DebugContent`, `MarkdownContent`,
`useAwaitCompentData`, `useParams`
- Added `sendFormMessage` from `useSendSessionMessage()` hook
- Added `useAwaitCompentData` hook for form state management
- Added `DebugContent` as `MessageItem` children for the latest
assistant message (renders UserFillUp form)
- Added `MarkdownContent` + submitted values display for previous
assistant messages
- Updated `NextMessageInput` disabled states to respect `isWaitting`
(form submission in progress)

## Test plan

- [x] Agent with UserFillUp component (e.g., email draft with
send/edit/cancel options) shows interactive form in **explore mode**
- [x] Same agent continues to work correctly in **run (editor) mode**
- [x] Form submission sends data back to the agent and workflow
continues
- [x] Input field is disabled while waiting for form submission
- [ ] Agents without UserFillUp components are unaffected in explore
mode

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Zhichang Yu <yuzhichang@gmail.com>

api/apps/restful_apis/agent_api.py

@@ -575,7 +575,14 @@ async def _iter_session_completion_events(tenant_id, agent_id, req, return_trace
             yield ans
             continue
 
-        if event in ["message", "message_end"]:
+        if event in ["message", "message_end", "user_inputs", "workflow_finished"]:
+            if event in ["user_inputs", "workflow_finished"]:
+                logging.debug(
+                    "Forwarding session completion event: tenant_id=%s agent_id=%s event=%s",
+                    tenant_id,
+                    agent_id,
+                    event,
+                )
             yield ans
 
 
@@ -1564,7 +1571,10 @@ async def agent_chat_completion(tenant_id, agent_id=None):
                             "trace": [copy.deepcopy(data)],
                         }
                     )
-            final_ans = ans
+            if ans.get("event") == "message_end":
+                final_ans = ans
+            elif ans.get("event") == "user_inputs" and not final_ans:
+                final_ans = ans
         except Exception as exc:
             return get_result(data=f"**ERROR**: {str(exc)}")