fix: leave out core files the core refuses by size

A core extra resolved by name shipped on existence platforms even when
the core's own size check turns the copy away. The RetroPie pack carried
the 128 KB Apple IIGS ROM as Basilisk II's ROM (min 512 KB). The builder,
the manifest and verify now read validation.core_size_refusal, which
accepts a copy any version of the same profile slot takes.

scripts/validation.py

@@ -9,7 +9,7 @@ from __future__ import annotations
 
 import os
 import zipfile
-from collections.abc import Callable, Iterator, Mapping
+from collections.abc import Callable, Iterator, Mapping, Sequence
 
 from common import (
     adler32_of,
@@ -961,3 +961,53 @@ def existence_discrepancy(file_entry: dict, local_path: str, platform_display: s
         f"packed per {platform_display} existence check: declared hash {declared}, "
         f"file md5 {actual['md5']} sha1 {actual['sha1']}"
     )
+
+
+def same_slot_entries(files: list, name: str, path: str) -> list[dict]:
+    """The entries of one profile that name the same file at the same path.
+
+    A profile lists every version its code takes under one name (each GRP
+    of Raze's table, eduke32's demo and retail NWINTER.GRP): any of them
+    fills the slot.
+    """
+    return [
+        entry for entry in files or []
+        if isinstance(entry, dict) and entry.get("name") == name
+        and (entry.get("path") or name) == path
+    ]
+
+
+def extra_alternatives(fe: dict, profiles: Mapping | None) -> list[dict]:
+    """The versions the extra's own profile accepts at the extra's slot."""
+    if not profiles:
+        return []
+    profile = profiles.get(fe.get("source_profile") or "", {})
+    name = fe.get("source_name") or fe.get("name", "")
+    return same_slot_entries(
+        profile.get("files") or [], name, fe.get("source_path") or name
+    )
+
+
+def core_size_refusal(
+    file_entry: dict, local_path: str | None, alternatives: Sequence[dict] = (),
+) -> str | None:
+    """Why the core refuses this copy by the size its own code checks, or None.
+
+    The one rule the builder, the install manifest and verify read for a
+    core's file. An existence platform never opens the bytes, so a copy whose
+    hash disagrees still ships to it, but a core that measures the file turns
+    one of the wrong size away: Basilisk II stops on the Apple IIGS' 128 KB
+    ROM (main_unix.cpp:692), so packing that file for it serves nothing.
+    ``alternatives`` are the other versions the profile accepts at the same
+    slot: a copy any of them takes is not refused.
+    """
+    if not local_path or not os.path.isfile(local_path):
+        return None
+    size = os.path.getsize(local_path)
+    if any(name_match_size_ok(entry, size) for entry in (file_entry, *alternatives)):
+        return None
+    bounds = (
+        f"{file_entry['size']}" if file_entry.get("size") is not None
+        else f"{file_entry.get('min_size', 0)} to {file_entry.get('max_size', 'any')}"
+    )
+    return f"{size} bytes, the core checks for {bounds}"