[BUG] AskUserQuestion: partial submit discards all already-provided answers

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When AskUserQuestion bundles multiple questions in a single call and the user answers some but not all of them, all answers are discarded — the tool result returns is_error: true with no answers payload. The model proceeds as if the user never responded, and any free-text content the user typed into the answered question is silently lost.

Same root-cause as #33511 (closed as not planned), different trigger: there it's the "Chat about this" button; here it's simply not interacting with one of the bundled questions before submitting.

What Should Happen?

Submit should return the partial answer set; unanswered questions are flagged explicitly (e.g. answers: {Q1: "..."}, unanswered: ["Q2"]), not erased. is_error: true should be reserved for genuine cancellation (Esc-Esc with zero interaction).

Error Messages/Logs

Steps to Reproduce

1. Model calls AskUserQuestion with two questions:

• Q1: "Which background-job library — Celery, ARQ, or APScheduler?" (Other → free-text)
• Q2: "Redis or RabbitMQ as the broker?" → Redis / RabbitMQ

1. User picks "Other" on Q1 and types a detailed paragraph explaining that the service doesn't need a queue at all — FastAPI BackgroundTasks covers the current load. Q2 is now moot, so user submits without picking either option.
2. Tool result returned to the model: is_error: true, no answers. The Q1 paragraph is gone — neither the model nor the user can recover it.

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

v2.1.119

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PyCharm terminal

Additional Information

_No response_