## Summary
- Make typed slash commands become text elements when the user hits
space, including paste‑burst spaces.
- Enable `/plan` to accept inline args and submit them in plan mode,
mirroring `/review` behavior and blocking submission while a task is
running.
- Preserve text elements/attachments for slash commands that take args.
<img width="1510" height="500" alt="image"
src="https://github.com/user-attachments/assets/446024df-b69a-4249-85db-1a85110e07f1"
/>
## Changes
- Add safe helper to insert element ranges in the textarea.
- Extend command‑with‑args pipeline to carry text elements and reuse
submission prep.
- Update `/plan` dispatch to switch to plan mode then submit prompt +
elements.
- Document new composer behavior and add tests.
## Notes
- `/plan` is blocked during active tasks (same as `/review`).
- Slash‑command elementization recognizes built‑ins and `/prompts:`
custom commands only.
## Codex author
`codex fork 019c16d3-4520-7bb0-9b9d-48720d40a8ab`
3392c5af24