Update iso-prototype.py

src/iso-prototype.py

@@ -507,11 +507,6 @@ def rebuild_windows_eltorito(iso, tree: Path) -> None:
     print(f"  BIOS: {bios_source} ({bios_source.stat().st_size} bytes)")
     print(f"  UEFI: {uefi_source} ({uefi_source.stat().st_size} bytes)")
 
-    # Remove the imported catalog before touching any inode referenced by it.
-    # This also releases PyCdlib's incomplete hidden boot-image records.
-    if getattr(iso, "eltorito_boot_catalog", None) is not None:
-        iso.rm_eltorito()
-
     # These private root-level records avoid depending on the source ISO's very
     # small ISO9660 tree.  The original Microsoft files remain available via UDF.
     for iso_path in (bios_iso_path, uefi_iso_path):
@@ -567,6 +562,15 @@ def build_pycdlib(args: argparse.Namespace) -> None:
     try:
         print(f"Opening source ISO: {source}")
         iso.open(str(source))
+
+        # PyCdlib stores directory-child indexes on imported hidden El Torito
+        # records. Any file removal/addition can make those indexes stale, which
+        # makes a later rm_eltorito() fail with "Invalid child index to remove".
+        # Remove the imported catalog immediately, before mutating the ISO tree.
+        if getattr(iso, "eltorito_boot_catalog", None) is not None:
+            print("Removing imported El Torito catalog before filesystem changes...")
+            iso.rm_eltorito()
+
         for value in args.replace:
             logical = PurePosixPath("/") / value.lstrip("/")
             print(f"Replacing: {logical}")