update skill

stage0/.claude/skills/port-astgen/SKILL.md

@@ -92,8 +92,11 @@ continue to Step 7 (commit progress, re-skip).
    a TODO comment describing the remaining diff.
 2. Remove ALL `fprintf`/`printf` debug statements from `astgen.c`.
 3. Remove `#include <stdio.h>` if it was added for debugging.
-4. Verify: `zig build fmt-zig0 && zig build all-zig0 -Dvalgrind` must exit 0
-   with no unexpected output.
+
+4. Verify this exits 0 with no unexpected output:
+
+    zig build fmt-zig0 && zig build all-zig0 -Dvalgrind |& grep -v Warning
+
 5. Commit:
    ```sh
    git add astgen.c astgen_test.zig