Note about checkpointing

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

@@ -88,6 +88,8 @@ continue to Step 7 (commit progress, re-skip).
 
 ### Step 7: Clean up and commit
 
+If progress was made (see Step 6), we need to checkpoint it by committing.
+
 1. If the corpus test still fails: re-add the `SkipZigTest` line with
    a TODO comment describing the remaining diff.
 2. Remove ALL `fprintf`/`printf` debug statements from `astgen.c`.