fix(core): retain ask_user question text in the tool result display - #29677

Summary

After answering an ask_user dialog, the completed tool block in the chat
history showed only the short header chip and the answer
(e.g. Retry Subagent → Yes). The question itself — which for yesno prompts
often carries the entire explanation — disappeared, leaving the human with no
context for the recorded decision, both in the live session and after
/resume.

This PR keeps the full question text in the Ask User result display, with the
answer nested beneath it.

Before

✓  Ask User

User answered:
  Retry Subagent → Yes

After

✓  Ask User

User answered:
  Retry Subagent: The subagent failed because the build step timed out. Would you like to retry it?
    → Yes

Details

Root cause — two independent decisions combine to drop the information:

1. ToolInfo (packages/cli/src/ui/components/messages/ToolShared.tsx)
   deliberately hides the tool description (Asking user: …) once an Ask User
   call reaches a terminal status, on the assumption that "the result display
   speaks for itself" (feat: wire up AskUserTool with dialog #17411).
2. AskUserInvocation.execute() (packages/core/src/tools/ask-user.ts) built
   returnDisplay from only question.header (a ≤16-char chip label) plus the
   answer; question.question was never emitted.

Once the modal closes, no rendered surface contains the question text.

Fix — a formatting-only change in AskUserInvocation.execute():

• Each answered question is rendered as <header>: <question> followed by
  → <answer>. Multi-line questions/answers keep their continuation lines
  aligned, and multiple questions are unambiguously paired with their answers.
• The defensive fallback for an answer index without a matching question
  (Q<index>) is preserved.
• llmContent (what the model receives) and the telemetry data payload are
  unchanged, so there is no impact on model behaviour or metrics.
• Because /resume rebuilds tool blocks from the persisted resultDisplay,
  resumed sessions retain the question as well.

Design decision — this intentionally does not add a settings toggle
(unlike the earlier attempt in #29022, which touched 10 files to plumb a
ui.keepAskUserQuestionsInHistory flag through Config). There is no scenario
in which hiding the question benefits the person reading the scrollback, and the
cost is one extra line per answered question. Default-on keeps the change
surgical and avoids settings-schema/docs churn.

The lines are rendered through the existing Markdown path; the leading spaces and
→ prefix are plain text (not list markers), verified by rendering through
ToolGroupMessage with Ink.

Related Issues

Fixes #29021
Related to #29022 (previous attempt, closed as stale)

How to Validate

1. Unit tests (includes a regression test mirroring the reporter's scenario,
   plus coverage for multi-question pairing, multi-line answers, multi-line
   questions, and the positional fallback):

   npm test -w @google/gemini-cli-core -- src/tools/ask-user.test.ts

   Expected: 35 tests pass. On main, the regression test
   should retain the question text in returnDisplay after answering (#29021)
   fails with expected '**User answered:**\n Retry Subagent …' to contain 'The subagent failed because the build…'.

2. Manual check:

   npm run build && npm start

   Prompt: Use the ask_user tool to ask me a yes/no question whose text explains that a build timed out and asks whether to retry. Answer the
   dialog. The completed Ask User block should now show
   Retry: <full question text> followed by → Yes. Run /resume on the
   session afterwards and confirm the question is still visible.

3. Edge cases covered by tests: multiple questions (each paired with its answer,
   in order), multi-line text answers (continuation lines aligned under the
   answer), multi-line questions (continuation lines indented), and an answer
   whose index has no matching question (Q<index> fallback).

Local CI parity: npm run preflight (clean, install, format, build, all
linters, typecheck, test:ci) passes.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed) — not needed:
  docs/tools/ask-user.md documents parameters and llmContent, neither of
  which changed.
• Added/updated tests (if needed)
• Noted breaking changes (if any) — none; display string only.
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker