For the 5 second undo. let `space` can pause it

[dacec354]

along with shortcut toggle last message's fold, it would be a nice experience .

[esengine]

Implemented the first half — `space` now pauses / resumes the 5-second undo countdown indefinitely. Bar freezes at the captured fraction, badge shows `Ns · paused`, press `space` again to resume. PR #356.

For the second half (shortcut to toggle last-message fold) — a couple of design questions before I can build it:

1. Which "last message" — the most recent assistant reply (the streaming card after it settles), the most recent tool output, or whichever card is currently last on screen?
2. What does "folded" look like — single-line summary (`▸ reply (1.2k tok · 42 t/s)`), or just hidden entirely with a placeholder?
3. Keystroke — `ctrl-f`? `f`? Shift+something? The ones that don't collide with existing bindings are mostly the ctrl- variants.

Could you split this into a separate issue with one of the answers above? It'll keep the PR scoped + the discussion in one place. Closing this one once #356 lands; the fold toggle can pick up its own number.

[esengine]

Both halves shipped: space pauses the undo countdown (PR #356), ctrl-o expands / re-collapses the live message (PR #359). The settled-message fold is constrained by Ink's <Static> already-flushed-to-scrollback semantics, but the live-card toggle covers the practical need.