Fix toolchain

tmp/default.do

@@ -3,15 +3,17 @@
 
 exec >&2
 
+pfx=${2%.rw}
+
 redo-ifchange ../flake.nix ../flake.lock || true
 
 resolve_flake() {
-    STORE_PATH=$(nix flake info --json --inputs-from .. "$2" | jq -r .path)
+    STORE_PATH=$(nix flake info --json --inputs-from .. "$pfx" | jq -r .path)
 
     # Do this after 'info' to avoid unnecessary network activity. nix flake
     # archive may try to download a flake although the store path is available.
     if [ ! -d "$STORE_PATH" ]; then
-        nix flake archive --inputs-from .. "$2"
+        nix flake archive --inputs-from .. "$pfx"
     fi
 }