UserPromptSubmit hook receives empty prompt when user_input is list[ContentPart]

What version of Kimi Code CLI is running?

kimi, version 1.41.0

Which open platform/subscription were you using?

kimi

Which model were you using?

kimi-k2.6

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

Bug: UserPromptSubmit hook receives empty prompt when user_input is list[ContentPart]
The UserPromptSubmit hook receives an empty prompt field when the user's input is formatted as a list of ContentPart o
bjects (which is the default for all messages).
Root cause in kimi_cli/soul/kimisoul.py line 601:
text_input_for_hook = user_input if isinstance(user_input, str) else ""
When user_input is list[ContentPart], it becomes "" and the hook receives empty prompt.
Expected: extract text from ContentPart list like it's done later:
user_message = Message(role="user", content=user_input)
text_input = user_message.extract_text(" ").strip()
Actual hook payload:
{
"hook_event_name": "UserPromptSubmit",
"session_id": "...",
"cwd": "...",
"prompt": ""
}

What steps can reproduce the bug?

1. Configure a UserPromptSubmit hook in ~/.kimi/config.toml
2. Start Kimi CLI and send any message
3. Check the hook's stdin — prompt field is always empty
   What is the expected behavior?
   The hook should receive the actual text content of the user's message, extracted from ContentPart objects.
   Additional information
   • Environment: kimi-cli v1.41.0, Windows 11, Python 3.13
   • This affects the Beta hooks system introduced in v1.28.0
   • The matcher_value parameter also receives empty string, making regex matching ineffective

What is the expected behavior?

No response

Additional information

No response

Start in kimi_cli/soul/kimisoul.py around line 601, where text_input_for_hook is prepared, and compare it with the later Message.extract_text(" ").strip() path. Ensure UserPromptSubmit receives the extracted text for list[ContentPart] input and that matcher_value uses the same text. Done means the hook payload contains the user's message instead of an empty prompt.