Constant NON_GIT_TREE_CACHE_SKIP_HINT 

pub const NON_GIT_TREE_CACHE_SKIP_HINT: &str = "skipping cache — source tree is not a git repository so dirty \
     state cannot be detected; put the source under git, or replace the \
     `--kernel <path>` source with one of the content-keyed fetch modes \
     that does not need dirty-state detection — `kernel build --kernel \
     <version>` (downloads the tarball from kernel.org) or `kernel build \
     --kernel git+URL#branch=NAME` (shallow-clones the given ref) — to \
     enable caching";

Hint shown in place of DIRTY_TREE_CACHE_SKIP_HINT when the source tree is not a git repository at all. commit / stash are not actionable remediations in that case — the operator’s only path to caching is to put the source under git (or use a kernel-source fetch mode that produces a git-tracked tree). Pinned by non_git_tree_cache_skip_hint_shape below so a wording drift is caught in unit tests.