ACP: AskUserQuestion/QuestionRequest resolves empty — structured questions unusable over ACP

Summary

In ACP server mode (kimi acp), AskUserQuestion cannot work: the ACP session resolves every QuestionRequest with an empty answer dict, so the model always receives {"answers": {}, "note": "User dismissed the question without answering."} — even when the user is present and willing to answer. ACP clients (Paseo, Zed, JetBrains AI Chat, …) therefore can never render the question's options or return a selection.

Observed downstream effect (kimi-code 0.23.6 driven by Paseo over ACP): the tool call surfaces as a generic permission card containing the raw {"questions": [...]} JSON with only Reject/Accept buttons — the user has no way to pick an option, and if the card is ignored the agent turn hangs indefinitely.

Current behavior

src/kimi_cli/acp/session.py (~line 211):

case QuestionRequest():
    logger.warning("QuestionRequest is unsupported in ACP session; resolving empty answer.")
    msg.resolve({})

The empty resolve is indistinguishable from a genuine user dismissal, so the model gets no signal that the client was the problem and may retry the tool.

Why this matters

• AskUserQuestion is the documented way for the agent to collect decisions mid-task; over ACP it is silently broken.
• The Wire protocol already solves this (QuestionRequest + supports_question capability negotiation in initialize); ACP has no equivalent path at all.
• The ask_user tool already contains a graceful fallback for unsupported clients (except QuestionNotSupported → ToolError: "Do NOT call this tool again. Ask the user directly in your text response instead."), but the ACP layer never raises it.

Proposals

Short-term (one line, helps every ACP client immediately):

case QuestionRequest():
    msg.set_exception(QuestionNotSupported())

This routes into the existing ToolError fallback, so the model asks its question in plain text — far better than a phantom dismissal or a hang.

Full support (either or both):

1. Map QuestionRequest to session/request_permission, encoding each question option as a permission option (option id = label, kind allow_once), and translate the selected option id back into answers. Covers the common single-question case; multi-question could be sequential requests. Multi-select has no clean mapping.
2. Add an ACP extension method (e.g. _kimi/questionRequest) carrying the full QuestionItem[] payload with a structured response, so capable clients can render multi-question / multi-select panels; clients advertise support via an extension capability.

References

• ACP session handling: https://github.com/MoonshotAI/kimi-cli/blob/main/src/kimi_cli/acp/session.py
• ask_user tool (empty-answer and QuestionNotSupported paths): https://github.com/MoonshotAI/kimi-cli/blob/main/src/kimi_cli/tools/ask_user/__init__.py
• QuestionRequest / QuestionNotSupported definitions (resolve / set_exception): https://github.com/MoonshotAI/kimi-cli/blob/main/src/kimi_cli/wire/types.py
• Downstream client-side companion issue (Paseo rendering of ACP questions): https://github.com/getpaseo/paseo/issues/2048

Start in src/kimi_cli/acp/session.py around the QuestionRequest case, then read the QuestionNotSupported fallback in src/kimi_cli/tools/ask_user/init.py and its definition in src/kimi_cli/wire/types.py. Determine which supported behavior the issue should use: the short-term fallback or a full ACP question mapping. Done means ACP no longer resolves an unanswered question as an empty answer and the model receives the intended fallback or structured response.