[Regression in 1.131] vscode_askQuestions auto-fills "user is not available" instead of prompting; Plan mode also auto-switches to Agent

## Type
Bug (regression)

## Summary
After upgrading to VS Code 1.131.0 + Copilot extension 0.59.0, two related
agent-mode regressions appeared:

1. The `vscode_askQuestions` tool no longer reliably waits for the user.
It auto-fills the answer with the exact string
`"The user is not available to respond and will review your work later.
Work autonomously and make good decisions."` and returns `skipped: false`,
so the agent proceeds as if the user had explicitly said "go autonomous".
2. In Plan mode, the session is sometimes auto-switched to Agent mode and
begins executing edits, instead of staying in the read-only plan state.

Both were observed in the same session right after the upgrade. Issue #315598
(the same askQuestions symptom) was closed as completed in May 2026, so this
looks like a regression introduced by 1.131 / Copilot 0.59. The Plan-mode
auto-switch matches the open issue #323274.

## Environment
- VS Code: 1.131.0
- Copilot extension: 0.59.0
- OS: Windows (Constrained Language Mode PowerShell)
- The offending session was started under 1.130.0 / Copilot 0.58.0 and
continued after the editor auto-upgraded to 1.131.0 / 0.59.0 mid-session.
The session's debug log (main.jsonl) contains two `session_start` events
confirming the in-session version bump, and both bugs occurred in the
post-upgrade window.

## Reproduction (Bug 1 — askQuestions auto-fill)
1. Start an agent session in Copilot Chat (1.131.0 / 0.59.0).
2. Ask the agent to confirm a non-trivial plan before editing, e.g.
"confirm your understanding is correct, then modify generate_xlsx.py".
3. The agent calls `vscode_askQuestions` with options + `allowFreeformInput: true`.
4. Do NOT interact with the popup for a short time (or be typing a free-text
answer that hasn't been submitted yet).
5. The tool returns:
```json
{
"answers": {
"": {
"selected": [],
"freeText": "The user is not available to respond and will review your work later. Work autonomously and make good decisions.",
"skipped": false
}
}
}
The agent, seeing skipped: false and that freeText, proceeds to edit
files autonomously — the user never approved.
Expected: the tool should either block until the user responds, or return
skipped: true so the agent knows to stop. Auto-injecting a "go autonomous"
directive with skipped: false is the worst of both worlds.

Reproduction (Bug 2 — Plan mode auto-switch)
Put Copilot Chat into Plan mode.
Ask the agent to plan a multi-file change.
At some point during planning, the session switches to Agent mode on its
own and begins applying edits, bypassing the plan handoff.
Matches open issue #323274 ("switching from Agent to Plan mode
mid-conversation auto-injects 'Start implementation' and begins executing").
Adding here as a +1 with the 1.131 regression angle.

Workaround
Until fixed, vscode_askQuestions cannot be relied on as an approval gate.
We have to either use Plan mode (which Bug 2 also undermines) or have the
agent ask confirmation as plain text in its reply and then stop, without
calling the tool.

Logs / evidence available
Session debug log with dual session_start events showing the in-session
version bump (1.130→1.131, 0.58→0.59).
Full transcript showing the askQuestions call and the auto-filled
"not available" response, plus the agent's subsequent autonomous edits.
Can attach on request.
Related
#315598 (closed/completed — original askQuestions fix, now regressed)
#315050 (duplicate of #314419 — tokenizer variant)
#300926 (PR that introduced chat.autoReply mechanism)
#323274 (open — Plan→Agent auto-switch)
#323074 (open — related mode-switch bug)