[FEATURE]: simpler history interaction and management #16355

Feature hasn't been suggested before.

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Describe the enhancement you want to request

The behaviour of history is "complex". Ctrl-X U undoes in the visible history, Ctrl-X R redoes in the visible history, up-arrow navigates to previous historical entries, but in the current entry box. Some combinations of undo/redo via Ctrl-X seem to create bugs where the lines are duplicated. I think there is unclear interaction between git snapshots / worktrees going on in the background as you undo and redo. Behavior seems to get even more complex if multiple instances of opencode are being used in the same directory tree at different levels at the same time.

I'd propose a simple Ctrl-UpArrow to actually visually navigate through (i.e., highlight) past message history, include the agent's side of the conversation, with a midnight-commander style command bar of common options for that item type displayed below it: regenerate, copy to input editor, copy, save to file, etc.

This has the advantage of becoming more capable over time: options like spawn in text editor, delete, revert code to this point, fork in a new instance with a new worktree, spawn a new agent from this point with a different task, etc. all become possible with this message history navigation approach.

Other tickets are proposing Ctrl-R to do a reverse history search, matching GNU Readline and other tools. This would fit naturally here as the forward/reverse history searches could visibly select the match in the history, were you'd see the surrounding context too.