refactor: name the gap filter's two kinds of skip

find_undeclared_files decided per entry whether a core requirement can
be a gap, through a chain that mixed two skips whose difference is easy
to lose. Some record the requirement as settled so no other profile
reconsiders it; the rest leave it open, because the same file can be
libretro-only in one profile and standalone-only in another and the key
carries no emulator.

The chain returns a named verdict now, complexity 60 to 45. Twelve tests
cover the verdicts and two more cover the distinction end to end: a
standalone-only entry seen first must not answer for the profile that
needs the file. Collapsing the two skips into one passes every other
test in the suite and fails that pair.

scripts/verify.py

@@ -338,6 +338,49 @@ def _name_in_index(
     return False
 
 
+def _candidate_verdict(
+    file_entry: dict,
+    fname: str,
+    is_standalone: bool,
+    include_all: bool,
+    declared_names: set,
+) -> str:
+    """Whether a profile entry can be a gap, and whether it is settled.
+
+    Three answers. "keep" means it is a candidate. "settled" means something
+    has answered for it -the platform declares it, or the profile documents
+    it as unsourceable -so the same requirement reached from another profile
+    must not be reconsidered. "skip" means it does not apply in this context,
+    which leaves it open for a profile where it does: the same file can be
+    libretro-only here and standalone-only there.
+    """
+    if file_entry.get("unsourceable"):
+        return "settled"
+    # Placeholders stand for a family of files, not a file.
+    if "<" in fname or ">" in fname or "*" in fname:
+        return "skip"
+    # An explicit null path means the user imports it through the UI.
+    if "path" in file_entry and file_entry["path"] is None:
+        return "skip"
+    file_mode = file_entry.get("mode")
+    if file_mode == "standalone" and not is_standalone:
+        return "skip"
+    if file_mode == "libretro" and is_standalone:
+        return "skip"
+    # Read from somewhere other than the system directory: not a BIOS gap.
+    load_from = file_entry.get("load_from", "")
+    if load_from and load_from != "system_dir":
+        return "skip"
+    # Filename-agnostic entries are answered by the builder's own scan.
+    if file_entry.get("agnostic"):
+        return "skip"
+    if not include_all:
+        archive = file_entry.get("archive")
+        if fname in declared_names or (archive and archive in declared_names):
+            return "settled"
+    return "keep"
+
+
 def find_undeclared_files(
     config: dict,
     emulators_dir: str,
@@ -425,42 +468,16 @@ def find_undeclared_files(
             )
             if not fname or seen_key in seen_files:
                 continue
-            # Skip unsourceable files (documented reason, not a gap)
-            if f.get("unsourceable"):
+            verdict = _candidate_verdict(
+                f, fname, is_standalone, include_all, declared_names
+            )
+            if verdict == "settled":
                 seen_files.add(seen_key)
                 continue
-            # Skip pattern placeholders (e.g., <user-selected>.bin)
-            if "<" in fname or ">" in fname or "*" in fname:
-                continue
-            # Skip UI-imported files with explicit path: null (not resolvable by pack)
-            if "path" in f and f["path"] is None:
-                continue
-            # Mode filtering: skip files incompatible with platform's usage
-            file_mode = f.get("mode")
-            if file_mode == "standalone" and not is_standalone:
-                continue
-            if file_mode == "libretro" and is_standalone:
-                continue
-            # Skip files loaded from non-system directories (save_dir, content_dir)
-            load_from = f.get("load_from", "")
-            if load_from and load_from != "system_dir":
-                continue
-
-            # Skip agnostic files (filename-agnostic, handled by agnostic scan)
-            if f.get("agnostic"):
+            if verdict == "skip":
                 continue
 
             archive = f.get("archive")
-
-            # Skip files declared by the platform (by name or archive)
-            if not include_all:
-                if fname in declared_names:
-                    seen_files.add(seen_key)
-                    continue
-                if archive and archive in declared_names:
-                    seen_files.add(seen_key)
-                    continue
-
             seen_files.add(seen_key)
 
             # Archived files are grouped by archive