diff --git a/routes.py b/routes.py
index b93306a9..509c1630 100644
--- a/routes.py
+++ b/routes.py
@@ -2361,8 +2361,10 @@ def _pick_installed_primary_vst(rs_gear: str, known_lookup: dict) -> dict | None
     for cand in candidates:
         if not isinstance(cand, dict):
             continue
-        if cand.get("bundled"):
-            continue
+        # Thin packaged builds download Rig Builder VSTs into the writable
+        # config root instead of _plugin_dir. _build_known_vst_lookup() scans
+        # both roots, so a missing read-only bundle must still fall back to its
+        # detected plugin name here.
         if not cand.get("name") or not known_lookup:
             continue
         installed = known_lookup.get(cand["name"].lower())
diff --git a/tests/test_vst_primary_resolution.py b/tests/test_vst_primary_resolution.py
new file mode 100644
index 00000000..b4ce9ccd
--- /dev/null
+++ b/tests/test_vst_primary_resolution.py
@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def _routes_module():
+    spec = importlib.util.spec_from_file_location(
+        "rig_builder_routes_for_vst_primary_test", ROOT / "routes.py"
+    )
+    assert spec and spec.loader
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def _candidate():
+    return {
+        "name": "Chorus",
+        "format": "VST3",
+        "bundled": "vst/pedals/CH-2.vst3",
+    }
+
+
+def test_primary_prefers_plugin_directory_bundle(tmp_path):
+    routes = _routes_module()
+    routes._plugin_dir = tmp_path / "read-only-plugin"
+    bundle = routes._plugin_dir / "vst" / "pedals" / "CH-2.vst3"
+    bundle.mkdir(parents=True)
+    routes._load_vst_seed_catalog = lambda: {"Pedal_Chorus": [_candidate()]}
+
+    downloaded = tmp_path / "writable-pack" / "pedals" / "Chorus.vst3"
+    known = {
+        "chorus": [
+            {"path": str(downloaded), "format": "VST3", "name": "Chorus"}
+        ]
+    }
+
+    assert routes._pick_installed_primary_vst("Pedal_Chorus", known) == {
+        "vst_path": str(bundle),
+        "vst_format": "VST3",
+    }
+
+
+def test_primary_falls_back_to_downloaded_pack_for_bundled_candidate(tmp_path):
+    routes = _routes_module()
+    routes._plugin_dir = tmp_path / "read-only-plugin"
+    routes._load_vst_seed_catalog = lambda: {"Pedal_Chorus": [_candidate()]}
+
+    downloaded = tmp_path / "writable-pack" / "pedals" / "Chorus.vst3"
+    known = {
+        "chorus": [
+            {"path": str(downloaded), "format": "VST3", "name": "Chorus"}
+        ]
+    }
+
+    assert routes._pick_installed_primary_vst("Pedal_Chorus", known) == {
+        "vst_path": str(downloaded),
+        "vst_format": "VST3",
+    }