PYTEST_BASETEMP was created at parse time via $(shell mktemp -d ...), so every make invocation — install, clean, doctor, tab completion — leaked an empty basetemp dir. Each make test also got its own unique basetemp, defeating pytest's built-in 3-run rotation and orphaning the contents. 1,109 dirs / 69GB had accumulated. Move creation into the recipe shell via PYTEST_BASETEMP_INIT (mktemp + trap) and prepend it to every recipe line that uses PYTEST_BASETEMP_FLAG. Trap removes the basetemp on EXIT/INT/TERM, so test runs no longer leak full dirs either.