fix(tests): serialize all env-touching tests on the crate-wide mutex - #12
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`cargo test --lib` failed reliably on a 14-core machine: 20 of 352 tests failed, all cascading from a single race. Three modules opted out of the crate-wide lock in [lib.rs](src/lib.rs#L21). `client` and `secrets` each declared their own module-private `ENV_MUTEX`, so their guards serialized only against tests in the same module. The 17 `client` tests that set `HOME` therefore ran concurrently with the `config`, `run` and `sandbox` tests that the crate-wide mutex serializes; `config::tests::agent_filesystem_paths_resolved` read another test's `HOME`, panicked while holding the crate-wide mutex, and poisoned it for the 19 further tests that `unwrap()` that lock. Four `exec` tests took no lock at all. They compare `build_env()`'s snapshot of the environment against a second `std::env::var` read of the same variable, and `ESSENTIAL_VARS` covers `HOME`, `LANG`, `LC_ALL` and `TZ` — all mutated by `run` tests, so the value could change between the two reads. With every env-touching test on one mutex, 40 consecutive parallel runs pass, so the Nix package no longer needs `dontUseCargoParallelTests`. Claude-Session: https://claude.ai/code/session_01E3R8fS7y8zYjoEzjorYTBJ
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cargo test --libfailed reliably on a 14-core machine: 20 of 352 tests failed, all cascading from a single race. Three modules opted out of the crate-wide lock in lib.rs.clientandsecretseach declared their own module-privateENV_MUTEX, so their guards serialized only against tests in the same module. The 17clienttests that setHOMEtherefore ran concurrently with theconfig,runandsandboxtests that the crate-wide mutex serializes;config::tests::agent_filesystem_paths_resolvedread another test'sHOME, panicked while holding the crate-wide mutex, and poisoned it for the 19 further tests thatunwrap()that lock.Four
exectests took no lock at all. They comparebuild_env()'s snapshot of the environment against a secondstd::env::varread of the same variable, andESSENTIAL_VARScoversHOME,LANG,LC_ALLandTZ— all mutated byruntests, so the value could change between the two reads.With every env-touching test on one mutex, 40 consecutive parallel runs pass, so the Nix package no longer needs
dontUseCargoParallelTests.Claude-Session: https://claude.ai/code/session_01E3R8fS7y8zYjoEzjorYTBJ