we have a very unclear lifecycle for the chatwidget—this should only
have to be added in one place! but this fixes the "hanging commands"
issue where the active_exec_cell wasn't correctly cleared when commands
finished.
To repro w/o this PR:
1. prompt "run sleep 10"
2. once the command starts running, press <kbd>Esc</kbd>
3. prompt "run echo hi"
Expected:
```
✓ Completed
└ ⌨️ echo hi
codex
hi
```
Actual:
```
⚙︎ Working
└ ⌨️ echo hi
▌ Ask Codex to do anything
```
i.e. the "Working" never changes to "Completed".
The bug is fixed with this PR.
afc377bae5