fix: choose regions among the files required-only keeps

scripts/generate_pack.py

@@ -520,6 +520,7 @@ def _select_variants(
     source: str,
     regions,
     one_per_slot: bool,
+    required_only: bool = False,
 ) -> tuple[set, list, list]:
     """Which regional and slot alternatives this pack leaves out.
 
@@ -545,6 +546,7 @@ def _select_variants(
             target_cores=target_cores,
             include_extras=(source != "platform"),
             include_all=(source == "truth"),
+            required_only=required_only,
         )
     if regions:
         region_index = region_mod.build_region_index(emu_profiles or {})
@@ -704,7 +706,7 @@ def generate_pack(
     # direction. Runs only when --region is given.
     region_drops, region_fallbacks, slot_undecidable = _select_variants(
         config, pack_systems, emulators_dir, db, base_dest, emu_profiles,
-        target_cores, source, regions, one_per_slot,
+        target_cores, source, regions, one_per_slot, required_only,
     )
 
     with zipfile.ZipFile(zip_path, "w", zipfile.ZIP_DEFLATED) as zf:
@@ -3077,6 +3079,7 @@ def generate_manifest(
             target_cores=target_cores,
             include_extras=(source != "platform"),
             include_all=(source == "truth"),
+            required_only=required_only,
         )
         region_drops = region_mod.resolve_region_drops(
             region_groups, region_index, regions

scripts/packextras.py

@@ -626,6 +626,7 @@ def platform_region_groups(
     target_cores: set[str] | None = None,
     include_extras: bool = True,
     include_all: bool = False,
+    required_only: bool = False,
 ) -> tuple[dict[str, list[tuple[str, str]]], dict[tuple[str, str, str], str]]:
     """Group a platform's pack candidates the way region filtering reads them.
 
@@ -639,6 +640,10 @@ def platform_region_groups(
     for sys_id, system in systems.items():
         members = groups.setdefault(sys_id, [])
         for file_entry in system.get("files", []):
+            if required_only and file_entry.get("required") is False:
+                # Decided over what the pack keeps: an optional winner
+                # removed afterwards left its slot empty.
+                continue
             dest = sanitize_pack_path(
                 file_entry.get("destination", file_entry.get("name", ""))
             )
@@ -659,6 +664,8 @@ def platform_region_groups(
         target_cores=target_cores,
         include_all=include_all,
     ):
+        if required_only and extra.get("required") is False:
+            continue
         dest = sanitize_pack_path(extra.get("destination", extra.get("name", "")))
         if not dest:
             continue