update skill

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

@@ -13,11 +13,11 @@ from Zig, copy the Zig structure into C.
 
 ## Key files
 
-- `astgen.c` — C implementation (modify this)
-- `astgen_test.zig` — corpus tests (enable/skip tests here)
-- `~/code/zig/lib/std/zig/AstGen.zig` — upstream reference (~14k lines)
-- `~/code/zig/lib/std/zig/Ast.zig` — AST node accessors
-- `~/code/zig/lib/std/zig/Zir.zig` — ZIR instruction definitions
+- `stage0/astgen.c` — C implementation (modify this)
+- `stage0/astgen_test.zig` — corpus tests (enable/skip tests here)
+- `lib/std/zig/AstGen.zig` — upstream reference (~14k lines)
+- `lib/std/zig/Ast.zig` — AST node accessors
+- `lib/std/zig/Zir.zig` — ZIR instruction definitions
 
 ## Loop
 
@@ -39,7 +39,7 @@ Remove or comment out the `if (true) return error.SkipZigTest` line.
 ### Step 3: Run tests
 
 ```sh
-zig build test 2>&1
+zig build test-zig0 2>&1
 ```
 
 Record the output. If tests pass, go to Step 7.
@@ -75,7 +75,7 @@ mechanically.
 ### Step 6: Port the fix
 
 Apply the minimal mechanical change to `astgen.c` to match the upstream.
-Run `zig build test` after each change to check for progress.
+Run `zig build test-zig0` after each change to check for progress.
 
 **Progress** means any of:
 - `inst_len` diff decreased
@@ -92,7 +92,8 @@ 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 && zig build all` must exit 0 with no unexpected output.
+4. Verify: `zig build fmt-zig0 && zig build all-zig0 -Dvalgrind` must exit 0
+   with no unexpected output.
 5. Commit:
    ```sh
    git add astgen.c astgen_test.zig