fix: agree on missing files in system packs

The emulator pack recorded only loose files as a path's occupant, so a
path an archive or data tree had filled was reported missing even with
the same bytes in the ZIP, and an archive several profiles ask for was
counted once per profile. verify registered neither, and credited one
profile's file at a path holding another's. Both now record archives
and tree members in pack order; --system snk-neogeo-mvs went from 113
missing in the pack and 51 in verify to 59 on both sides.

scripts/generate_pack.py

@@ -1176,11 +1176,14 @@ def _pack_data_tree(
     seen_destinations: set[str],
     seen_parents: set[str],
     seen_lower: set[str],
+    packed_at: dict[str, str] | None = None,
 ) -> int:
     """Write one data directory into an emulator pack, under its shared lock.
 
     A refresh swaps the tree by rename; without the lock a walk half done
-    read the old tree and wrote files of the new one.
+    read the old tree and wrote files of the new one. ``packed_at`` records
+    each member, so a later profile asking for the same bytes there is
+    served rather than reported missing.
     """
     added = 0
     with cache_lock(local_cache, shared=True):
@@ -1197,6 +1200,8 @@ def _pack_data_tree(
                 _register_path(full, seen_destinations, seen_parents)
                 seen_lower.add(full.lower())
                 _add_pack_member(zf, src, full)
+                if packed_at is not None:
+                    packed_at[full.lower()] = src
                 added += 1
     return added
 
@@ -1294,6 +1299,15 @@ def generate_emulator_pack(
     # Loose file packed at each folded destination, to tell a profile asking
     # for the same file there from one asking for other bytes.
     packed_at: dict[str, str] = {}
+    # A destination is missing once, however many profiles ask for it:
+    # verify --emulator counts by destination.
+    missing_at: set[str] = set()
+
+    def report_missing(name: str, destination: str) -> None:
+        if destination not in missing_at:
+            missing_at.add(destination)
+            missing_files.append(name)
+
     data_dir_notices: list[str] = []
     data_registry = load_data_dir_registry(
         platforms_dir or os.path.join(os.path.dirname(__file__), "..", "platforms")
@@ -1348,9 +1362,10 @@ def generate_emulator_pack(
                     seen_destinations.add(archive_dest)
                     _register_path(archive_dest, seen_destinations, seen_parents)
                     seen_lower.add(archive_dest.lower())
+                    packed_at[archive_dest.lower()] = local_path
                     total_files += 1
                 else:
-                    missing_files.append(archive_name)
+                    report_missing(archive_name, archive_dest)
 
             # Pack individual files (skip archived ones). The entries of one
             # profile on one destination are the releases the code accepts
@@ -1456,7 +1471,7 @@ def generate_emulator_pack(
                         ):
                             # The file already at this path, asked for twice.
                             continue
-                        missing_files.append(alternatives[0]["name"])
+                        report_missing(alternatives[0]["name"], dest)
                         continue
 
                 if chosen is None:
@@ -1465,7 +1480,7 @@ def generate_emulator_pack(
                     elif all(fe.get("unsourceable") for fe in alternatives):
                         unsourceable_files.append(alternatives[0]["name"])
                     else:
-                        missing_files.append(alternatives[0]["name"])
+                        report_missing(alternatives[0]["name"], dest)
                     continue
 
                 fe, local_path, how = chosen
@@ -1535,7 +1550,8 @@ def generate_emulator_pack(
                     if prefix:
                         dd_dest = f"{prefix}/{dd_dest}" if dd_dest else prefix
                 total_files += _pack_data_tree(
-                    zf, local_cache, dd_dest, seen_destinations, seen_parents, seen_lower
+                    zf, local_cache, dd_dest, seen_destinations, seen_parents, seen_lower,
+                    packed_at,
                 )
 
     # Remove empty ZIP (no files packed and no missing = nothing to ship)