Check the OpenVMM child's descriptors in the inheritance test

[Pedro Henrique Penna (ppenna)]

Summary

openvmm_inherits_no_descriptor_beyond_its_standard_streams could fail even though OpenVMM inherits nothing.

• Before: the test makes a pipe writer inheritable while it spawns a child, then waited up to 2 s for the pipe's reader to reach end-of-file. A plain child that a concurrent test spawned in that window also inherited the writer and kept the pipe open past the timeout. An example is the python3 child of a_process_runs_until_its_last_thread_exits.
• Now: the test reads the spawned child's own /proc/PID/fd and looks for the planted pipe. Command::spawn returns once the child has executed its program, which closes its close-on-exec copies, so any copy that remains was inherited. The result no longer depends on other processes or on a timeout, and the test takes milliseconds instead of more than 2 s.

Only the test changes. I found this while investigating flaky guest tool tests in #528, which had the same kind of descriptor race. This test was never seen failing on its own, because a long-lived plain child has to start within a window of about a millisecond.

Validation

• WSL Linux, on 4927f941: every check-nvx-rs and check-aci-edge-sandboxes command passed. That covers formatting, Clippy, tests with all and with default features, the bundled-artifact fixture, agent bundling, rustdoc, Rust 1.89, and the macOS cross-check.
• Repeated runs: the fixed test passed 200 consecutive runs, 527 ms in total. Its module, which includes the python3 test, passed 100 runs, 10 at a time.
• Reproduction: a scratch-only test started a bystander plain child while the writer was inheritable. The old check reported a leak after 3.0 s; the new one correctly reported none in 1.2 ms.

[Copilot]

🟢 Approval recommended

The focused test-only change removes the cross-test race without identified blocking issues.

0 open findings

What changed in this PR

Makes the Linux descriptor-inheritance test inspect the intended child directly, avoiding false failures caused by concurrent tests.

Changes:

• Replaces pipe EOF timeouts with /proc/PID/fd inspection.
• Preserves leak detection checks and child cleanup.

File	Description
nvx-rs/​src/​host/​process.rs	Updates the test helper and callers to check child descriptors directly.

🧠 Review effort: Balanced

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[Copilot]

🟢 Approval recommended

The focused test-only change removes cross-process interference while preserving leak detection and cleanup, with no unresolved findings.

0 open findings

🧠 Review effort: Balanced