// Each cargo test run of this project spawns its own set of integration-test
// binaries, and each one of those binaries normally inherits the crate root as
// its cwd. The hegel library creates `.hegel/` in the process's cwd, so
// without this setup the test binaries would all share (and clobber) one
// `.hegel/` inside the crate root across concurrent and successive `cargo
// test` runs. This ctor chdir's every test binary into its own tempdir before
// main, so each binary's `.hegel/` lands in a fresh, private location.
//
// Note: this is purely a test-harness concern. The library's documented
// behaviour (`.hegel/` in the caller's cwd) is deliberate for real users.
static TEST_CWD: OnceLock = new;