rust-i18n's i18n! macro embeds all ~31k translations (9 locales) into one generated backend-init function. In debug builds the compiler does not reuse stack slots, so that single frame is ~1.5 MB, and coverage instrumentation inflates it several times over. The first t!() call triggers the init on a libtest worker thread, whose default 2 MB stack overflows under coverage (Linux) or the smaller effective stack (Windows), aborting the run. Release builds optimize the frame away, so only the test harness is affected. Set RUST_MIN_STACK=16 MiB via .cargo/config.toml [env] so every cargo/nextest test process (and rustc) gets ample stack regardless of platform or coverage.