Feature Request: Add unified diff view + configurable default (and optional auto mode)

[nordrune]

Hi :)

Please add a unified (inline) diff view. Split view is hard to read for me, especially with small changes and limited horizontal space (terminal/tiled splits, even on big monitors). In tools like Cloud Code, unified works much better for quick reviews. (IMO)

Proposal

Implement unified diff view alongside split.

Make the default diff view configurable in opencode.json.

Optional Auto mode: use unified for small diffs, switch to split when changes exceed a configurable threshold.

Why

Unified is more compact and easier to scan for small edits.

Split consumes too much horizontal space in my setup and slows me down.

Defaults

Consider unified as the default (subject to team validation), with easy toggle to Split/Auto.

[benvinegar]

Adding a +1, opencode often looks like this for me – I almost always have to switch to my editor to see what's happening.

[rekram1-node]

Yeah I think once opentui migration is complete things like better diffs will be prioritized

[duguyue100]

This would be very much needed, another user who cannot stand the split view here.

[jdanbrown]

+1, here's what split diffs look like for me with 154 columns (using opencode 1.0.23). I find it too visually jumbled to make much sense of it at a glance.

(Also, background highlights are missing in 1.0, tracked here: https://github.com/sst/opencode/issues/3687)