[Bug] Space key conflict in agent view reply box prevents text input for new agent line

**Bug Description**
agent view "space for reply" is very confusing and frustrating.

before I used to press space to know I was in the box and then start typing because then the cursor moved.

Can we have the option of different key please? Space is used for typing

And I guess sometimes for voice within this thing. But yeah, opening the reply box with a different letter would probably be a little bit better.

Took me about 15 minutes to work out that I needed to press the letter keys to fill in the box and that the space key wouldn't fill in the box anymore. That was really, really, really annoying.

**Environment Info**
- Platform: linux
- Terminal: xterm-256color
- Version: 2.1.271
- Feedback ID: e746bb4b-f25a-400d-ae0d-d06d6b28a801

**Errors**
```json
[]
```

No files or tests are named. Start by reproducing the conflict in the agent view reply box on Linux with xterm-256color, then trace the key handling for opening and typing in the box. Done means the reply box opens without consuming space as a text character, and space can be entered normally while composing a new agent line.

Written by the indexing model from the issue text.