Voice message send button intermittently missing when recording in a thread

## Steps to reproduce

1. Open the desktop app and navigate to a room with threads
2. Open a thread
3. Press the voice message button in the thread composer and start recording
4. Observe the composer send button

## Outcome

**What did you expect?**
The send button appears in the composer while recording.

**What happened instead?**
The send button does not appear. The waveform and stop button are visible, but the composer send button is missing. The only way out is to cancel the recording. Occurs intermittently.

## Environment

- **OS**: macOS
- **Application version**: Element 1.12.15
- **Installed from**: https://element.io/get-started
- **Homeserver**: Private homeserver
- **Rageshake**: No

Start by reproducing the intermittent behavior in the desktop app's thread composer while recording a voice message. Trace the thread composer, voice-message controls, and send-button state, then verify that the send button consistently appears during recording without preventing cancellation.

Written by the indexing model from the issue text.