Fix tmux statusline color leaking into alt screen

[MeteorSkyOne]

Description

Fixes a tmux rendering issue where transient status line background colors could leak into the alternate screen and Warp footer background inference while shell initialization is still settling.

The change does two things:

• Clears a fresh DECSET 1049 alternate screen with the terminal default background instead of the current cursor template background.
• Samples empty ligature-rendered rows as transparent/default background so tmux statusline colors do not become the inferred alternate-screen background.

Linked Issue

No matching upstream issue found for this focused bug fix.

Screenshots / Videos

The agent tooltip bar becomes green when ligature is enabled.

Testing

• cargo fmt -p warp
• cargo test -p warp test_enter_alt_screen_clears_with_default_background
• cargo test -p warp tmux_
• cargo test -p warp alt_reset
• cargo clippy -p warp --all-targets --tests -- -D warnings
• cargo clippy --locked --workspace --exclude warp_completer --all-targets --tests -- -D warnings
• cargo clippy --locked -p warp_completer --all-targets --tests -- -D warnings

Also attempted cargo clippy --workspace --all-targets --all-features --tests -- -D warnings, but in this local external setup it enables release_bundle without an installed private warp-channel-config binary, so the warp build script does not generate local/dev/preview/stable_config.json and the app bins fail at include_str!. The current script/presubmit and CI lint workflow use the --workspace --exclude warp_completer --all-targets --tests clippy command above instead, with a repo TODO to re-enable --all-features later.

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

Changelog Entries for Stable

CHANGELOG-BUG-FIX: Fixed tmux status line colors leaking into alternate screen background rendering.

Co-Authored-By: Warp agent@warp.dev

[cla-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have the users @MeteorSkyOne on file. In order for us to review and merge your code, each contributor must visit https://cla.warp.dev to read and agree to our CLA. Once you have done so, please comment @cla-bot check to trigger another check.

[oz-for-oss]

@MeteorSkyOne

I'm starting a first review of this pull request.

You can view the conversation on Warp.

I reviewed this pull request and requested human review from: @warpdotdev/oss-maintainers.

Comment /oz-review on this pull request to retrigger a review (up to 3 times on the same pull request).

Powered by Oz

[MeteorSkyOne]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[oz-for-oss]

Overview

This PR adjusts alternate-screen clearing and ligature-rendered empty-row background sampling so transient tmux status-line backgrounds do not seed the alternate-screen/footer background inference.

Concerns

• No blocking correctness, security, or performance concerns identified in the changed lines.

Verdict

Found: 0 critical, 0 important, 0 suggestions

Approve

Comment /oz-review on this pull request to retrigger a review (up to 3 times on the same pull request).

Powered by Oz