fix: resolve UE5 audio test race condition

[AndrewAltimit]

Summary

• Fix flaky unload_track_fires_callback test that broke main CI by adding a Mutex to serialize tests sharing global callback atomics (LAST_EVENT/LAST_TRACK/LAST_VALUE)
• Fix unused variable warning (port -> _port) in oasis-app test
• Main CI and PR validation pipelines already run identical test suites -- the root cause was the race condition itself, not a pipeline gap

Root Cause

The UE5 audio tests use static AtomicU32 globals written by an extern "C" callback. When Rust runs tests in parallel, one test's reset_globals() can overwrite another's callback values between the action and the assertion. The failing assertion saw u32::MAX (reset sentinel) instead of 6 (TrackUnloaded).

Fix

init_backend() now acquires a Mutex guard that serializes all callback-dependent tests. The guard lives for the test's lifetime via destructuring: let (_guard, mut b) = init_backend();. Tests that don't use callbacks (e.g. default_state, has_audio_*) are unaffected.

Test plan

• cargo test -p oasis-backend-ue5 -- audio -- all 22 tests pass
• cargo test --workspace -- full suite passes
• cargo clippy --workspace -- -D warnings -- clean
• cargo fmt --all -- --check -- clean

Generated with Claude Code

[github-actions]

Gemini AI Code Review

Issues (if any)

(none)

Previous Issues (for incremental reviews)

(none)

Suggestions (if any)

(none)

Notes

• The unused variable warning fix in oasis-app/src/commands.rs is correct.
• Lock poisoning is properly handled via unwrap_or_else(|e| e.into_inner()), which correctly prevents one panicking test from cascading failures to other tests.
• The let (_guard, mut b) binding correctly ensures the MutexGuard lives until the end of the test scope (unlike let _ = ... which would drop immediately), successfully preventing the race condition on the shared atomic variables.

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Generated by Gemini AI (gemini-3.1-pro-preview). Supplementary to human reviews.

[github-actions]

Codex AI Code Review

Issues (if any)

(none)

Previous Issues (for incremental reviews)

(none)

Suggestions (if any)

• crates/oasis-app/src/commands.rs:599 - Remove let _port = 0; entirely since it is no longer used and the simulation is already represented by state.listener = Some(...).

Notes

• Verified both changed files and line references in the provided diff; no actionable bugs or security issues were identified.
• The mutex-guard lifetime pattern in crates/oasis-backend-ue5/src/audio.rs correctly serializes callback-atomic tests and addresses the stated race condition.

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Generated by Codex AI (gpt-5.3-codex). Supplementary to human reviews.

[AndrewAltimit]

Review Response Agent (Iteration 1)

Status: No changes needed

Fixed Issues

• Removed dead let _port = 0; variable in crates/oasis-app/src/commands.rs:599 per Codex suggestion - the binding was entirely unused and should be deleted rather than suppressed with an underscore prefix

Ignored Issues

• (none - both Gemini and Codex found no bugs or security issues)

Deferred to Human

• (none)

Notes

• Both Gemini and Codex gave the PR a clean review with no issues found
• Gemini explicitly validated the mutex-guard lifetime pattern and poison handling as correct
• The only actionable item was Codex's minor suggestion to remove the dead variable entirely, which has been applied and verified with clippy + test compilation

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The agent reviewed feedback but determined no code changes were required.

[github-actions]

Gemini AI Incremental Review

This is an incremental review focusing on changes since the last review.

Previous Issues

• [RESOLVED] crates/oasis-app/src/commands.rs:596 - Unused port variable removed entirely based on previous feedback.

Issues

(none)

Suggestions

(none)

Notes

• The Mutex in crates/oasis-backend-ue5/src/audio.rs serializes access to shared global callback atomics, effectively addressing the test race condition.
• Capturing the MutexGuard as _guard correctly holds the lock for the full duration of each test.
• Using unwrap_or_else(|e| e.into_inner()) to handle lock poisoning is good defensive practice — prevents a single failing test from deadlocking or cascading failures across the suite.

---

Generated by Gemini AI (gemini-3.1-pro-preview). Supplementary to human reviews.

[github-actions]

Codex AI Incremental Review

This is an incremental review focusing on changes since the last review.

Issues (if any)

(none)

Previous Issues (for incremental reviews)

• [RESOLVED] crates/oasis-app/src/commands.rs:596 - Unused port test variable was removed.

Suggestions (if any)

(none)

Notes

• Verified the two changed files in the diff; no new actionable bugs, security issues, or required fixes were identified.
• The test-lock change in crates/oasis-backend-ue5/src/audio.rs correctly serializes callback-global assertions and addresses the reported race condition pattern.

---

Generated by Codex AI (gpt-5.3-codex). Supplementary to human reviews.

[AndrewAltimit]

Review Response Agent (Iteration 2)

Status: No changes needed

Fixed Issues

• (none needed - all previous feedback was already addressed in iteration 1)

Ignored Issues

• (none - both Gemini and Codex incremental reviews found zero issues or suggestions)

Deferred to Human

• (none)

Notes

• Both Gemini (gemini-3.1-pro-preview) and Codex (gpt-5.3-codex) gave clean incremental reviews with no issues, no suggestions, and confirmed the previous Codex suggestion (remove dead port variable) as resolved
• The mutex-guard pattern and poison handling in crates/oasis-backend-ue5/src/audio.rs were validated as correct by both reviewers
• No code changes required for this iteration

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The agent reviewed feedback but determined no code changes were required.