diff --git a/.gitea/workflows/release-macos.yaml b/.gitea/workflows/release-macos.yaml
index 8f75829..628f29e 100644
--- a/.gitea/workflows/release-macos.yaml
+++ b/.gitea/workflows/release-macos.yaml
@@ -84,12 +84,21 @@ jobs:
         # The runner wipes the workspace each run, so cargo target/ never
         # accumulates. Bound the persistent nix store by generation: record the
         # current devShell as a generation of a persistent profile (in $HOME),
-        # keep the 2 newest, reclaim what older ones referenced.
+        # keep the 2 newest, reclaim what older ones referenced — so the
+        # toolchain stays *warm* across runs and only stale generations are GC'd.
+        #
+        # The profile's parent dir MUST exist first, or `nix develop --profile`
+        # errors ("cannot read directory …") and the profile/gc-root is never
+        # created — which made `nix-collect-garbage` delete the whole toolchain
+        # closure every run (re-downloaded ~3.8 GiB each time; the retention was
+        # silently broken by the swallowed `|| true`). No `|| true` on the
+        # profile realization now: a future breakage should fail loudly.
         if: always()
         run: |
           echo "--- disk before ---"; df -h / | tail -1
           P="$HOME/.cache/rdbms-ci/toolchain"
-          nix develop --profile "$P" -c true || true
+          mkdir -p "$(dirname "$P")"
+          nix develop --profile "$P" -c true
           nix-env -p "$P" --delete-generations +2 || true
           nix-collect-garbage || true
           echo "--- disk after ---"; df -h / | tail -1