fix: isolate Linux SteamCMD user configuration

[be-student]

Change

Run Linux workshop downloads with HOME, XDG_CONFIG_HOME, and XDG_DATA_HOME under a dedicated home directory inside the configured SteamCMD prefix. SteamCMD no longer inherits the desktop Steam client's user-configuration paths. Refs #2419.

The first download, queued batches, and manual restart retain these overrides. Other inherited variables, including PATH, remain available. Windows and macOS retain their existing environment. Relative prefixes resolve to absolute isolation paths before launch. User documentation describes the dedicated directory.

Validation

Regression tests cover process wiring, absolute paths, relative prefixes, inherited variables, queued batches, restart, and non-Linux behavior.

• Final tests against base source: 6 failed, 14 passed.
• Same targeted files with the fix: 20 passed.
• uv run pytest --doctest-modules --no-qt-log -q: 1369 passed, 1 skipped.
• Full mypy: no issues in 282 source files; pyright: 0 errors/warnings.
• Changed-file Ruff and formatting, markdownlint, duplicate-code scan, deferred-import guard and git diff --check: passed.
• Whole-tree Ruff still reports an unrelated EXE001 on untouched app/__main__.py (its tracked file mode is not executable).

These checks ran on macOS. They verify environment construction and QProcess wiring; no real Linux SteamCMD run or desktop-library preservation trial was performed. Directory-creation errors fail before the subprocess starts rather than falling back to the desktop environment.

Agent disclosure

Generated and independently reviewed by OpenAI Codex for be-student. No human review has occurred before submission; maintainer review and Linux runtime verification are requested.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
app/utils/steam/steamcmd/wrapper.py	26.93% <100.00%> (+2.79%)	⬆️
app/windows/runner_panel.py	64.45% <100.00%> (+25.33%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[LionelColaso]

Nice catch looks Good Thanks