diff --git a/scripts/truth.py b/scripts/truth.py
index 4cced3f7..b2ce7a75 100644
--- a/scripts/truth.py
+++ b/scripts/truth.py
@@ -8,7 +8,7 @@ from __future__ import annotations
 
 import sys
 
-from common import _norm_system_id, resolve_platform_cores
+from common import _norm_system_id, resolve_platform_cores, runs_standalone
 from validation import filter_files_by_mode
 
 
@@ -22,28 +22,6 @@ def _serialize_source_ref(sr: object) -> str:
     return str(sr)
 
 
-def _determine_core_mode(
-    emu_name: str,
-    profile: dict,
-    cores_config: str | list | None,
-    standalone_set: set[str] | None,
-) -> str:
-    """Determine effective mode (libretro/standalone) for a resolved core."""
-    if cores_config == "all_libretro":
-        return "libretro"
-    if standalone_set is not None:
-        profile_names = {emu_name} | {str(c) for c in profile.get("cores", [])}
-        if profile_names & standalone_set:
-            return "standalone"
-        return "libretro"
-    ptype = profile.get("type", "libretro")
-    if "standalone" in ptype and "libretro" in ptype:
-        return "both"
-    if "standalone" in ptype:
-        return "standalone"
-    return "libretro"
-
-
 def _enrich_hashes(entry: dict, db: dict) -> None:
     """Fill missing sibling hashes from the database, ground-truth preserving.
 
@@ -288,13 +266,10 @@ def generate_platform_truth(
     Returns a dict with platform metadata, systems, and per-file details
     including which cores reference each file.
     """
-    cores_config = config.get("cores")
-
-    # Resolve standalone set for mode determination
-    standalone_set: set[str] | None = None
-    standalone_cores = config.get("standalone_cores")
-    if isinstance(standalone_cores, list):
-        standalone_set = {str(c) for c in standalone_cores}
+    # The layout rule verify and the pack builder apply: truth guessed its
+    # own from the profile type where the platform names no standalone
+    # emulator, and kept files the pack never carries.
+    standalone_set = {str(c) for c in config.get("standalone_cores") or []}
 
     resolved = resolve_platform_cores(config, profiles, target_cores)
 
@@ -347,14 +322,10 @@ def generate_platform_truth(
             continue
         cores_profiled.add(emu_name)
 
-        mode = _determine_core_mode(emu_name, profile, cores_config, standalone_set)
-        raw_files = profile.get("files", [])
-        if mode == "both":
-            filtered = raw_files
-        else:
-            filtered = filter_files_by_mode(
-                raw_files, standalone=(mode == "standalone")
-            )
+        filtered = filter_files_by_mode(
+            profile.get("files", []),
+            standalone=runs_standalone(emu_name, profile, standalone_set),
+        )
 
         for fe in filtered:
             profile_sid = fe.get("system", "")
diff --git a/tests/test_truth_layout.py b/tests/test_truth_layout.py
new file mode 100644
index 00000000..b87d3e89
--- /dev/null
+++ b/tests/test_truth_layout.py
@@ -0,0 +1,55 @@
+"""Truth lays a core out the way verify and the pack builder do.
+
+truth.py kept its own rule: with no standalone_cores it read the profile
+type, called a dual profile "both" and a standalone one "standalone", and
+kept `mode: standalone` files that runs_standalone, and so the pack, leave
+out on RetroBat, EmuDeck and RetroDECK.
+"""
+
+from __future__ import annotations
+
+import sys
+import unittest
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(REPO_ROOT / "scripts"))
+
+from truth import generate_platform_truth  # noqa: E402
+
+
+def _names(truth: dict) -> set[str]:
+    return {
+        f["name"]
+        for system in truth.get("systems", {}).values()
+        for f in system.get("files", [])
+    }
+
+
+class TruthFollowsRunsStandalone(unittest.TestCase):
+    PROFILE = {
+        "emulator": "Dual",
+        "type": "standalone + libretro",
+        "systems": ["sony-playstation"],
+        "files": [
+            {"name": "both.bin", "system": "sony-playstation", "md5": "a" * 32},
+            {"name": "only_sa.bin", "system": "sony-playstation", "md5": "b" * 32,
+             "mode": "standalone"},
+            {"name": "only_lr.bin", "system": "sony-playstation", "md5": "c" * 32,
+             "mode": "libretro"},
+        ],
+    }
+
+    def test_no_standalone_cores_means_libretro_layout(self):
+        config = {"cores": ["dual"], "systems": {}}
+        truth = generate_platform_truth("p", config, {}, {"dual": self.PROFILE})
+        self.assertEqual(_names(truth), {"both.bin", "only_lr.bin"})
+
+    def test_named_standalone_core_gets_its_files(self):
+        config = {"cores": ["dual"], "standalone_cores": ["dual"], "systems": {}}
+        truth = generate_platform_truth("p", config, {}, {"dual": self.PROFILE})
+        self.assertEqual(_names(truth), {"both.bin", "only_sa.bin"})
+
+
+if __name__ == "__main__":
+    unittest.main()