The prune step's profile path $HOME/.cache/rdbms-ci/toolchain had no
parent dir, so `nix develop --profile` errored ("cannot read directory")
and — swallowed by `|| true` — never created the profile/gc-root. With
nothing rooting the toolchain, nix-collect-garbage deleted the whole
closure every run (~3.8 GiB re-downloaded each dispatch; confirmed in the
run-74 log). Add `mkdir -p` for the parent and drop the `|| true` on the
profile realization so a future breakage fails loudly. The VM stays
bounded as before, but the toolchain now persists across runs.
release-macos.yaml is workflow_dispatch (runs from main's definition), so
this takes effect on the next dispatch — the already-published v0.2.0
macOS binaries are unaffected.
claude@clouddev1
3c87dbb391