Understands and extends the sane.mk GNU Make framework
for shared deps, check, build, test, dist, debug, and system workflows.
Detect a sane.mk repo by `include $(SANE_MK_ROOT)/...` in the Makefile or a
generated `Makefile.lazy` with `SANE_*` variables.
Use when:
* editing this repo
* adding Make targets/includes
* wiring behavior through `SANE_*` variables
* adopting sane.mk in another project
* debugging why a target is not reachable
* validating, linting, formatting, or testing in a sane.mk repo
(the entrypoint is `make check` / `make test`, never direct tool calls)
* editing any non-Make file in a sane.mk repo when you need to validate it
2026-07-10