diff --git a/test/core/bundled-sets.test.js b/test/core/bundled-sets.test.js
new file mode 100644
index 00000000..8f84761e
--- /dev/null
+++ b/test/core/bundled-sets.test.js
@@ -0,0 +1,26 @@
+// @ts-check
+
+import test from 'node:test'
+import assert from 'node:assert/strict'
+
+import { V1_BUNDLED_PLUGIN_ALLOWLIST, V1_EXCLUDED_FROM_DEFAULT } from '../../src/core/runtime/bundled.js'
+
+// The two sets are read by different code paths that must never disagree
+// about a name: `discoverBundledPlugins` checks the allowlist before the
+// exclude set, so a name in both lands in `loaded`, while
+// `ridersInDefaultSet` (src/core/cli/walkthrough.js) drops anything in
+// `V1_EXCLUDED_FROM_DEFAULT`. Coverage (the union spanning the bundled
+// workspace) does no work here; only disjointness keeps those two reads in
+// agreement (issue #761, follow-up to PR #757's round-2 review).
+test('the default-activation allowlist and the excluded set are disjoint', () => {
+  const overlap = [...V1_BUNDLED_PLUGIN_ALLOWLIST].filter((name) => V1_EXCLUDED_FROM_DEFAULT.has(name))
+  assert.deepEqual(
+    overlap,
+    [],
+    `plugin(s) ${overlap.join(', ')} appear in both V1_BUNDLED_PLUGIN_ALLOWLIST and `
+    + 'V1_EXCLUDED_FROM_DEFAULT: discoverBundledPlugins checks the allowlist first, so '
+    + 'these land in its `loaded` bucket while ridersInDefaultSet treats them as excluded. '
+    + 'Remove the name from whichever set does not match its intended default-activation '
+    + 'boundary.'
+  )
+})