refactor: one place decides which profiles answer

The verifier and the builder each resolved the profiles a run names, in
thirty-five lines that differed only in how they failed: one exits, the
other returns empty-handed. An alias is the same binary under another
name and a launcher only starts an emulator, so neither has requirements
of its own, and both refusals have to say the same thing.

common raises now and each caller chooses its own ending. Six tests hold
the refusals, one of them reading both sources so a copy cannot grow
back. The manifest's core-complement phase comes out of generate_manifest
in the same pass, 60 to 34.

Verified inert: manifests identical entry for entry, and the Handy pack
rebuilds to the same bytes.

scripts/verify.py

@@ -48,8 +48,10 @@ from common import (
     md5sum,
     require_yaml,
     resolve_local_file,
+    ProfileSelectionError,
     resolve_platform_cores,
     sanitize_pack_path,
+    select_emulator_profiles,
 )
 
 yaml = require_yaml()
@@ -1254,51 +1256,12 @@ def _select_profiles(
     all_profiles: dict,
     standalone: bool,
 ) -> list[tuple[str, dict]]:
-    """Resolve the named profiles, refusing the ones that answer for others.
-
-    An alias is the same binary under another name and a launcher only
-    starts an emulator, so neither has requirements of its own: naming
-    one is a question about the wrong profile, and the answer says which
-    one to ask instead.
-    """
-    # Resolve profile names, reject alias/launcher
-    selected: list[tuple[str, dict]] = []
-    for name in profile_names:
-        if name not in all_profiles:
-            available = sorted(
-                k
-                for k, v in all_profiles.items()
-                if v.get("type") not in ("alias", "test")
-            )
-            print(f"Error: emulator '{name}' not found", file=sys.stderr)
-            print(f"Available: {', '.join(available[:10])}...", file=sys.stderr)
-            sys.exit(1)
-        p = all_profiles[name]
-        if p.get("type") == "alias":
-            alias_of = p.get("alias_of", "?")
-            print(
-                f"Error: {name} is an alias of {alias_of} -use --emulator {alias_of}",
-                file=sys.stderr,
-            )
-            sys.exit(1)
-        if p.get("type") == "launcher":
-            print(
-                f"Error: {name} is a launcher -use the emulator it launches",
-                file=sys.stderr,
-            )
-            sys.exit(1)
-        # Check standalone capability
-        ptype = p.get("type", "libretro")
-        if standalone and "standalone" not in ptype:
-            print(
-                f"Error: {name} ({ptype}) does not support --standalone",
-                file=sys.stderr,
-            )
-            sys.exit(1)
-        selected.append((name, p))
-
-    return selected
-
+    """Resolve the named profiles, stopping the run on a bad name."""
+    try:
+        return select_emulator_profiles(profile_names, all_profiles, standalone)
+    except ProfileSelectionError as exc:
+        print(f"Error: {exc}", file=sys.stderr)
+        sys.exit(1)
 
 def verify_emulator(
     profile_names: list[str],