[Bug]: Integrated terminal advertises only 256 colors, so TUIs downsample truecolor #7648

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Open the integrated terminal.
2. Run a TUI that renders colored subprocess output. lazygit with delta as its diff pager is a good example. Open a commit diff.
3. Compare the same view in a native terminal like Ghostty or iTerm2.
4. Confirm the cause: run COLORTERM=truecolor lazygit in the same T3 terminal. The colors render correctly.

Expected behavior

24-bit colors render like a native terminal. delta's dim diff backgrounds show as dim red and green.

Actual behavior

lazygit downsamples delta's 24-bit colors to the 256-color palette, so the dim diff backgrounds land on the grey ramp and show grey instead of dim red and green.

Running the same delta output straight from the shell (git show | delta) looks correct, because that writes truecolor directly to the terminal and the embedded Ghostty VT renders it. The problem is limited to TUIs that render colored output through their own color layer: they see a 256-color terminal and downsample.

Screenshots in the T3 Code terminal: lazygit diff view (left) and lazygit launched with COLORTERM=truecolor lazygit (right) -- notice on the left screenshot the background color of the diffs is grey instead of red/green

Impact

Cosmetic issue

Version or commit

main @ 3b72d17 (v0.0.33 tag)

Environment

macOS 26.5.2, Desktop App

Logs or stack traces

Screenshots, recordings, or supporting files

See "Actual behavior" section

Workaround

The pty is spawned as xterm-256color with no COLORTERM set (echo $COLORTERM prints nothing), so TUIs detect a 256-color terminal and downsample truecolor output. Prefixing COLORTERM=truecolor fixes it. T3 embeds Ghostty, which advertises COLORTERM=truecolor natively, so it may be best to align on this as well.

Current workaround is to export COLORTERM=truecolor in your shell rc, or prefix the TUI.

I am running a build with a one-line fix on my fork (default COLORTERM=truecolor when spawning the pty). Not sure if this should need discussion before a PR: kyleawayan@0d973ce