fix: count a core file only where it is packed

verify kept its own copy of the placement rule and missed the flat RomM folder, so the report still counted 543 unreachable files as packed. It now asks the builder's ExtraPlacement. The README fraction counted every held core file, including those a platform cannot place or that a same-named packed file hides. It now counts what the pack holds.

scripts/packextras.py

@@ -224,27 +224,41 @@ def hidden_extras(
     return hidden
 
 
-def unplaceable_extras(config: dict, undeclared: list[dict], profiles: dict) -> set:
-    """Keys of the report entries a slug-based platform cannot place.
+def _extra_dest(u: dict) -> str:
+    """Where a report entry lands before any platform prefix.
+
+    An archive entry goes by the archive's name, and a directory path takes
+    the file's name after it ("cafeLibs/" + "snd_user.rpl").
+    """
+    archive = u.get("archive")
+    raw = archive if archive else (u.get("path") or u["name"])
+    return f"{raw}{u['name']}" if raw.endswith("/") else raw
+
+
+def unplaceable_extras(
+    config: dict, undeclared: list[dict], profiles: dict
+) -> dict[tuple[str, str, str], str]:
+    """The report entries a slug-based platform cannot place, with the reason.
 
     RomM files every BIOS under the slug of its system and knows no slug
-    for DOS or for the arcade sets MAME 2003 reads. The builder skipped
-    those entries and the report counted them in the pack.
+    for DOS or for the arcade sets MAME 2003 reads, and it lists each folder
+    flat. The builder skipped those entries and the report counted them in
+    the pack. The answer comes from the builder's own placement.
     """
-    from common import _norm_system_id
-
-    is_slug_based, sys_to_slug = _detect_slug_structure(config)
-    if not is_slug_based:
-        return set()
-    platform_systems = set(config.get("systems", {}).keys())
-    norm_map = {_norm_system_id(sid): sid for sid in platform_systems}
-    native = native_slug_systems(config)
-    return {
-        (u.get("emulator", ""), u.get("name", ""), u.get("path") or "")
-        for u in undeclared
-        if u.get("in_repo")
-        and not _slug_for(u, profiles, platform_systems, norm_map, sys_to_slug, native)
-    }
+    placement = ExtraPlacement(config, "", profiles)
+    if not placement.slug_based:
+        return {}
+    unplaced: dict[tuple[str, str, str], str] = {}
+    for u in undeclared:
+        if not u.get("in_repo"):
+            continue
+        dest = _extra_dest(u)
+        if placement.place(u, dest) is None:
+            key = (u.get("emulator", ""), u.get("name", ""), u.get("path") or "")
+            unplaced[key] = (
+                "below_platform_folder" if placement.nested(dest) else "no_platform_slug"
+            )
+    return unplaced
 
 
 def _agnostic_scan_extras(
@@ -795,9 +809,7 @@ def _collect_emulator_extras(
         # For archive entries, use the archive name for resolution
         archive = u.get("archive")
         name = archive if archive else u["name"]
-        raw_dest = archive if archive else (u.get("path") or u["name"])
-        # Directory path: append filename (e.g. "cafeLibs/" + "snd_user.rpl")
-        dest = f"{raw_dest}{u['name']}" if raw_dest.endswith("/") else raw_dest
+        dest = _extra_dest(u)
 
         # Slug-based platforms: prefix dest with system slug
         placed = placement.place(u, dest)