fix: use corepack yarn directly in _pick_yarn_cmd

npm_install.py

@@ -2003,23 +2003,22 @@ def _build_frontend(src_frontend: Path, dest_frontend: Path):
                 if DEBUG:
                     print(f"    debug pick: yarn_bin={yarn_bin} HANGS, skipping")
             
-        # Use npm exec directly (bypasses broken corepack proxy)
+        # Use corepack yarn directly (bypasses broken corepack proxy)
-        if shutil.which("npm"):
+        if shutil.which("corepack") and shutil.which("npm"):
             try:
                 result = subprocess.run(
-                    ["npm", "exec", "--yes", "yarn@stable", "--", "--version"],
+                    ["corepack", "yarn", "--version"],
-                    capture_output=True, text=True, timeout=30,
+                    capture_output=True, text=True, timeout=15,
                 )
                 if DEBUG:
-                    print(f"    debug pick: npm exec version={result.stdout.strip()} rc={result.returncode}")
+                    print(f"    debug pick: corepack yarn version={result.stdout.strip()} rc={result.returncode}")
-                major = _get_yarn_major_version(["npm", "exec", "--yes", "yarn@stable", "--"])
+                if result.returncode == 0:
-                if major and major >= 4:
+                    match = re.match(r'^(\d+)', result.stdout.strip())
-                    if DEBUG:
+                    if match and int(match.group(1)) >= 4:
-                        print(f"    debug pick: using npm exec for yarn")
+                        return ["corepack", "yarn"]
-                    return ["npm", "exec", "--yes", "yarn@stable", "--"]
             except Exception as e:
                 if DEBUG:
-                    print(f"    debug pick: npm exec failed: {e}")
+                    print(f"    debug pick: corepack yarn failed: {e}")
                 pass
         return None