Voice (PTT): typing during the finalize window drops the dictated transcript

### Summary

When using **push-to-talk (PTT) voice dictation** (hold the trigger key, speak, release), if I start typing before the final transcript lands, my **entire dictation is lost**. The grey "preview" text disappears and is replaced by whatever I type.

### Steps to reproduce

1. Place the cursor in the prompt input.
2. Hold the voice push-to-talk trigger, speak a sentence (the live transcription appears as **grey/dim preview text**), then release the key.
3. Immediately — before the text turns solid/committed (white) — type any character.

### Expected

The pending dictation should be committed first (the grey preview becomes real text), and my typed character should be appended after it. I should not lose what I dictated.

### Actual

The grey preview text is cleared and the finalized transcript is **dropped entirely**. Only the character I typed remains. The whole dictation is lost.

### Root cause (from inspecting the bundled `app.js`, v1.0.63)

The voice reactor hook (`ycr`) drives a small state machine: `idle → recording → finalizing → idle`.

- During recording, streaming partial transcripts are shown via the input controller's `setPreview(...)` — this is the **grey/dim preview** text.
- Releasing the PTT key calls `finishSession({ commit: true })` and moves to the `finalizing` state, while the speech engine **asynchronously** drains audio and returns the final transcript.
- The keyboard handler only intercepts/commits a keystroke when `mode === "dictation" && state === "recording"`:

```js
if (Fe && Fe.mode === "dictation" && x.current === "recording" && (he.length > 0 || ...))
return fe(), true; // commit + swallow the key
```

In **PTT mode**, and during the **`finalizing`** window, this guard is false, so the keystroke is **not** intercepted — it falls through into the input box and mutates the buffer.
- When `finishSession` resolves, the result handler (`ae`) clears the preview and, **for PTT specifically**, performs a strict snapshot check against the recording anchor:

```js
if (he.mode === "ptt") {
if (Ge.text !== he.anchor.before + he.anchor.after || Ge.cursorPosition !== he.anchor.pos) {
// logs: "ptt: snapshot diverged after release; dropped transcript"
return; // <-- DROPS the transcript
}
Ge.insertInput(...);
} else {
// dictation (toggle) mode: on divergence it still inserts at the current cursor (does NOT drop)
}
```

Because the user typed during the `finalizing` window, the input no longer matches the anchor, so the PTT branch hits the divergence guard and **drops the transcript**. Dictation (toggle) mode does **not** drop on divergence — it recovers by inserting at the current cursor. This asymmetry is the bug: PTT loses the dictation, toggle mode does not.

### Suggested fixes (either would resolve it)

1. **Queue keystrokes during `finalizing`**: while a session is finalizing, hold incoming keystrokes until the transcript is inserted (mirrors how dictation-while-recording already swallows the first keystroke to commit), then apply them. This commits the grey preview before the typed text.
2. **Make PTT recover like dictation**: on snapshot divergence, insert the committed transcript at the current cursor position instead of dropping it. This is the smaller change and preserves the dictation in every case.

### Environment

- GitHub Copilot CLI `v1.0.63`
- Platform: Linux
- Voice mode: push-to-talk (hold-to-talk)

先在 CLI 中重現 PTT 序列，接著檢查打包後的 app.js v1.0.63 中 voice reactor hook ycr、finishSession、keyboard handler 和 result handler ae 附近的程式碼。驗證在 finalizing 期間輸入內容時，待處理的 transcript 會被保留，並附加輸入的字元，而不是觸發因 snapshot divergence 導致的捨棄。

由索引模型根據 Issue 內容生成。