fix: group core files under their pack path

On a platform that writes bios/ in front of its destinations (RetroDECK, AmberELEC, EmuELEC), a core extra was grouped, dropped and held under its bare destination while the platform's declaration of the same file used bios/<name>. Beetle PSX's scph5501.bin was kept by the --region japan pack while the declaration was dropped and the installer dropped the path. extra_region_key keys every extra with the platform's declared root, in the builder, the manifest selection, verify's replay and the omissions. The same key gives the declared entries the systems of the core files at their path: every --system case of RetroDECK differed between pack and installer before, none does now.

scripts/packextras.py

@@ -62,6 +62,20 @@ def prefixed_destination(dest: str, prefix: str) -> str:
     return f"{prefix}/{dest}"
 
 
+def extra_region_key(fe: dict, prefix: str) -> str:
+    """The key a core extra is grouped, dropped and held under by --region.
+
+    Its destination with the BIOS directory the platform writes in front of
+    its own (declared_root): RetroDECK declares bios/scph5501.bin, and
+    Beetle PSX's scph5501.bin grouped bare was looked up under another key,
+    kept by the pack while the declaration of the same file was dropped,
+    and the installer, which records the path once, dropped it.
+    """
+    return prefixed_destination(
+        sanitize_pack_path(fe.get("destination", fe.get("name", ""))), prefix
+    )
+
+
 def save_entry_fields(fe: dict) -> dict:
     """What a manifest entry adds for a file read below the save directory.
 
@@ -364,6 +378,7 @@ def hidden_extras(
         content[dest.lower()] = sha1_by_path.get(local)
     lower = set(content) if case_insensitive else set()
     prefix = _detect_extras_prefix(config, base_dest)
+    region_prefix = declared_root(config)
     hidden: dict[tuple[str, str, str], str] = {}
     packed_keys: set[tuple[str, str, str]] = set()
     extras = _collect_emulator_extras(
@@ -377,7 +392,7 @@ def hidden_extras(
         if required_only and fe.get("required") is False:
             continue
         dest = sanitize_pack_path(fe.get("destination", fe.get("name", "")))
-        if not dest or (region_drops and dest in region_drops):
+        if not dest or (region_drops and extra_region_key(fe, region_prefix) in region_drops):
             continue
         full = extra_full_destination(fe, prefix)
         if not full:
@@ -1705,8 +1720,9 @@ def platform_region_groups(
     )
     held = {id(extra) for extra in extras}
     spellings = system_spellings(systems)
+    region_prefix = declared_root(config)
     for extra in _kept(extras + absent, required_only):
-        dest = sanitize_pack_path(extra.get("destination", extra.get("name", "")))
+        dest = extra_region_key(extra, region_prefix)
         if not dest:
             continue
         name = extra.get("name", "")