Feature request

Add Up/Down replay for prior user inputs in the desktop composer.

This is a new composer convenience feature. The original product does not currently provide user input history replay through the Up/Down keys.

Expected behavior

• Up recalls older user-visible inputs from the composer history.
• Down moves forward through recalled inputs and eventually restores the saved draft.
• Prompt history uses persisted user-visible session content, not runtime-expanded model prompts.
• The active session is searched first in its own time order.
• Cross-session history follows the sidebar/session sidecar order instead of globally interleaving prompts from parallel sessions by event timestamp.
• Session traversal is lazy: initialize from lightweight session order, then parse a session JSONL only when navigation reaches it.

Implementation direction

Use a tape-style cursor:

1. Start with the active session.
2. Walk the remaining sessions by sidebar/sidecar activity order.
3. Parse and cache prompt entries per session only when needed.
4. Page older prompts with a cursor so users can keep scrolling without up-front full-history scans.