diff --git a/frontend/js/views/device-detail.js b/frontend/js/views/device-detail.js
index fa2a917..8ee9b96 100644
--- a/frontend/js/views/device-detail.js
+++ b/frontend/js/views/device-detail.js
@@ -89,9 +89,8 @@ function renderDeviceClock(device) {
 // covers panels paired before that existed, which registered as "Chrome 120" with a BrightSign UA.
 function isBrightSignDevice(device) {
   if (!device) return false;
-  const platform = String(device.platform || '').toLowerCase();
-  if (platform.includes('brightsign')) return true;
-  return String(device.user_agent || '').toLowerCase().includes('brightsign');
+  // platform only: `devices` has no user_agent column, so a fallback on it could never fire.
+  return String(device.platform || '').toLowerCase().includes('brightsign');
 }
 
 export function render(container, deviceId) {
diff --git a/server/lib/sync-backend.js b/server/lib/sync-backend.js
index e77336b..e4858fd 100644
--- a/server/lib/sync-backend.js
+++ b/server/lib/sync-backend.js
@@ -24,16 +24,22 @@
 const BACKENDS = ['auto', 'screentinker', 'brightsign'];
 
 /*
- * A device is a BrightSign if it said so. The player sends ?platform=brightsign (autorun.brs
- * puts it there), which lands in devices.platform. The UA fallback covers players paired before
- * the port existed — those registered a platform of "Chrome 120" with a BrightSign UA.
+ * A device is a BrightSign if it said so: the player sends ?platform=brightsign (autorun.brs puts
+ * it there), which lands in devices.platform.
+ *
+ * There is deliberately NO user-agent fallback. An earlier version had one, to catch panels paired
+ * before this port existed — which registered as "Chrome 120" with a BrightSign user agent. It
+ * could never fire: `devices` has no user_agent column, so the field is always undefined on a row
+ * read from the database. It read as defensive and was dead code.
+ *
+ * Those pre-port panels are identified the moment they re-register on a build that carries the
+ * host, which every one of them gets on its next update. Recognising them earlier would mean
+ * persisting the user agent, and a column added solely to identify a population that disappears on
+ * its own is not worth carrying.
  */
 function isBrightSignDevice(device) {
   if (!device) return false;
-  const platform = String(device.platform || '').toLowerCase();
-  if (platform.includes('brightsign')) return true;
-  const ua = String(device.user_agent || '').toLowerCase();
-  return ua.includes('brightsign');
+  return String(device.platform || '').toLowerCase().includes('brightsign');
 }
 
 /*
diff --git a/server/test/sync-backend.test.js b/server/test/sync-backend.test.js
index 8e12216..d171596 100644
--- a/server/test/sync-backend.test.js
+++ b/server/test/sync-backend.test.js
@@ -66,11 +66,15 @@ test('unknown or missing settings read as auto rather than throwing', () => {
   assert.equal(resolveSyncBackend('auto', null).backend, 'screentinker');
 });
 
-test('a player paired before the port is still recognised by its user agent', () => {
-  // Both of giyokun's devices registered platform "Chrome 120" with a BrightSign UA.
+test('a pre-port panel is NOT recognised until it re-registers — no phantom user-agent match', () => {
+  // Panels paired before this port registered as "Chrome 120" with a BrightSign user agent, and an
+  // earlier version tried to catch them that way. It could never work: `devices` has no user_agent
+  // column, so the field is always undefined on a row read from the database — the check passed
+  // only in tests that fabricated it, which is exactly how dead code survives.
   const legacy = { id: 'old', platform: 'Chrome 120', user_agent: 'BrightSign/9.1.92.2 (HD1026) Chrome/120' };
-  assert.equal(isBrightSignDevice(legacy), true);
-  assert.equal(resolveSyncBackend('auto', [legacy, bs(2)]).backend, 'brightsign');
+  assert.equal(isBrightSignDevice(legacy), false, 'a fabricated user_agent must not create a match');
+  assert.equal(resolveSyncBackend('auto', [legacy, bs(2)]).backend, 'screentinker',
+    'so a group containing one reads as mixed until that panel re-registers as brightsign');
 });
 
 test('a non-BrightSign device is never mistaken for one', () => {