Constant KTSTR_KERNEL_COMMIT_ENV 

pub const KTSTR_KERNEL_COMMIT_ENV: &str = "KTSTR_KERNEL_COMMIT";

Name of the environment variable cargo-ktstr sets to a dir=commit;dir=commit;... map of each resolved SOURCE kernel’s short commit hash (with a -dirty suffix when the tree is dirty), keyed by the same directory string exported in KTSTR_KERNEL_ENV / KTSTR_KERNEL_LIST_ENV.

cargo-ktstr probes each kernel’s git HEAD ONCE in the orchestrator and records it here. The sidecar writer reads this map and looks itself up (by its own KTSTR_KERNEL dir) instead of re-running a gix HEAD read + dirty-walk over the kernel tree in every per-test nextest process. That walk is memoized per process but NOT across processes, so without this map each of N test processes re-pays the full dirty-walk (seconds on a large kernel checkout).

Optimization only: a missing entry, absent env, or decode failure falls back to the in-process resolve-and-walk, which is always correct. Kernels with no recoverable source tree (transient Range/Git specs, or a Version/CacheKey cache miss) are absent from the map, and the fallback yields the same None for them.