[FEATURE]: Truncate output of long scripts/diffs by default

[dansanduleac]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Claude's vscode extension, as well as Cursor's agent mode, have this nice feature where long diffs, or outputs, are truncated to only a few lines by default. This would also be nice in opencode, as it will make skimming past messages a lot easier.

Currently, scrolling through past messages requires wading through sometimes 50+ lines of diffs, or shell outputs. Even if we can later trim those, e.g. via opencode-dcp, my chats still feel pretty verbose to scroll through.

We could make these expand to the full height (maybe in a modal) if the user clicks on them, or runs a Ctrl+P action while focused on the message in question.

Example from Claude VSCode extension:

Example from Cursor: