ci: add virt stack etl traces to petri runs

Petri-based Test Diagnostics: Technical Summary & Next Steps

This summary captures the approach, technical feedback, and recommendations from PR #1656, which explored adding Windows WPR trace collection to petri-based tests in OpenVMM.

Approach

• Proposed automatic WPR trace collection during petri-based test runs.
• For each test, a WPR trace session was started/stopped, saving output to the test directory.
• Used an embedded WPR profile targeting OpenVMM/OpenHCL/Hyper-V.

Limitations & Feedback

• Process Isolation: Each test case ("trial" in libmimic) runs in its own process, with process spawning managed externally by cargo-nextest. This makes coordinated trace management challenging—there is no OpenVMM-specific code for process control.
• Test Runner Integration: Robust trace management should be handled by the test runner (flowey), which ought to start/stop trace sessions per test for reliability and isolation.
• Trace File Handling: Output management and clean-up introduce complexity, especially with parallel test execution.
• Profile Customization: The default WPR profile may not fit all scenarios; customization per test or suite is desirable.
• Platform Scope: Current solution is Windows-only.

Recommendations

• Delegate trace session lifecycle to the test runner (flowey).
• Make trace collection opt-in or configurable at the test/suite level.
• Support custom WPR profiles for targeted diagnostics.
• Consider platform-agnostic approaches if future needs arise.

This summary is intended for rapid onboarding and planning of diagnostic improvements for petri-based tests.

Start by reviewing PR #1656 and the trace-collection limitations described here, then read how flowey runs petri-based tests alongside libmimic and cargo-nextest. Define the trace-session lifecycle, configuration, profile handling, and output cleanup needed for isolated and parallel trials; done means the agreed flowey-based approach is implemented and validated for the supported Windows scenarios.