Add skill command env patching

checks/skill-build.nix

@@ -11,6 +11,30 @@ let
   discovered = discoverSkills ./fixtures/valid;
   built = map (skill: mkSkill { inherit pkgs; inherit (skill) name src; }) discovered;
 
+  commandSrc = pkgs.runCommandLocal "command-skill-src" { } ''
+    mkdir -p "$out"
+    printf '%s\n' '---' 'name: command-skill' 'description: Fixture skill with a command.' '---' \
+      > "$out/SKILL.md"
+    cat > "$out/run-command" <<'EOF'
+#!/usr/bin/env sh
+: "''${TOOL:=tool}" # mkSkill:TOOL
+exec "$TOOL" "$@"
+EOF
+    chmod +x "$out/run-command"
+  '';
+
+  commandSkill = mkSkill {
+    inherit pkgs;
+    name = "command-skill";
+    src = commandSrc;
+    commands = [
+      {
+        path = "run-command";
+        env.TOOL = "${pkgs.coreutils}/bin/printf";
+      }
+    ];
+  };
+
   collision = builtins.tryEval (discoverSkills ./fixtures/collision);
 
   discoveredNames = lib.sort (a: b: a < b) (map (skill: skill.name) discovered);
@@ -24,6 +48,7 @@ pkgs.runCommandLocal "skill-build-check"
     pairs = lib.concatStringsSep " " (map (skill: "${skill.skillName}=${skill}") built);
     collisionSucceeded = if collision.success then "yes" else "no";
     expectedNames = lib.concatStringsSep " " discoveredNames;
+    inherit commandSkill;
   }
   ''
     fail() { echo "FAIL: $1" >&2; exit 1; }
@@ -52,5 +77,11 @@ pkgs.runCommandLocal "skill-build-check"
     test -f "$beta_path/tools/SKILL.md" \
       || fail "beta's asset subfolder did not ride along into \$out"
 
+    echo "command tier: declared command env defaults are patched"
+    test -x "$commandSkill/run-command" \
+      || fail "declared command is not executable"
+    grep -qx ': "''${TOOL:=${pkgs.coreutils}/bin/printf}" # mkSkill:TOOL' "$commandSkill/run-command" \
+      || fail "declared command env default was not patched"
+
     touch "$out"
   ''