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>

test/unit_test/common/test_file_utils.py

@@ -53,23 +53,24 @@ class TestGetProjectBaseDirectory:
     def test_uses_environment_variable_when_available(self):
         """Test that function uses RAG_PROJECT_BASE environment variable when set"""
         test_path = "/custom/project/path"
-
-        file_utils.PROJECT_BASE = test_path
-
-        result = get_project_base_directory()
+        with patch.dict(os.environ, {"RAG_PROJECT_BASE": test_path}, clear=False):
+            result = get_project_base_directory()
         assert result == test_path
 
     def test_calculates_default_path_when_no_env_vars(self):
         """Test that function calculates default path when no environment variables are set"""
         with patch.dict(os.environ, {}, clear=True):  # Clear all environment variables
-            # Reset the global variable to force re-initialization
+            original_base = file_utils.PROJECT_BASE
+            try:
+                file_utils.PROJECT_BASE = None
+                result = get_project_base_directory()
 
-            result = get_project_base_directory()
-
-            # Should return a valid absolute path
-            assert result is not None
-            assert os.path.isabs(result)
-            assert os.path.basename(result) != ""  # Should not be root directory
+                # Should return a valid absolute path
+                assert result is not None
+                assert os.path.isabs(result)
+                assert os.path.basename(result) != ""  # Should not be root directory
+            finally:
+                file_utils.PROJECT_BASE = original_base
 
     def test_caches_project_base_value(self):
         """Test that PROJECT_BASE is cached after first calculation"""