CI only checked macOS and Windows before merge, so Linux-only Rust paths could fail cargo check for the first time during release packaging. The matrix now includes an Ubuntu lane that runs the same frontend build and backend cargo check, with only the Linux libraries needed for checking Tauri dependencies and no bundle step.
Constraint: Issue #300 asks for PR-time Linux validation while skipping Tauri bundle work.\nRejected: Add Linux release bundle to CI | too slow and duplicates release-tauri.yml.\nConfidence: high\nScope-risk: narrow\nTested: python ci.yml textual assertions; git diff --check; cd openless-all/app && npm run build; cd openless-all/app && cargo check --manifest-path src-tauri/Cargo.toml\nNot-tested: Full GitHub Actions ubuntu-latest runner execution before PR.\nRelated: https://github.com/appergb/openless/issues/300
H-Chris233
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