diff --git a/src/resources/extensions/gsd/tests/find-missing-summaries-closed.test.ts b/src/resources/extensions/gsd/tests/find-missing-summaries-closed.test.ts
new file mode 100644
index 000000000..a0d0d70b0
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/find-missing-summaries-closed.test.ts
@@ -0,0 +1,48 @@
+/**
+ * Regression test for #3669 — findMissingSummaries skips closed slices
+ *
+ * When a slice has status "skipped", "complete", or "done", it should be
+ * excluded from the missing-summary check because closed slices intentionally
+ * lack SUMMARY files (or their DB status is authoritative).
+ *
+ * This is a structural verification test — it reads the source to confirm the
+ * CLOSED_STATUSES guard exists at the filter site.
+ */
+
+import { describe, test } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+const source = readFileSync(join(__dirname, '..', 'auto-dispatch.ts'), 'utf-8');
+
+describe('findMissingSummaries closed-status exclusion (#3669)', () => {
+  test('CLOSED_STATUSES set includes skipped, complete, and done', () => {
+    // The source must define a CLOSED_STATUSES set with all three statuses
+    assert.match(source, /CLOSED_STATUSES.*=.*new Set\(/,
+      'CLOSED_STATUSES set should be defined');
+    assert.match(source, /"skipped"/, 'CLOSED_STATUSES should include "skipped"');
+    assert.match(source, /"complete"/, 'CLOSED_STATUSES should include "complete"');
+    assert.match(source, /"done"/, 'CLOSED_STATUSES should include "done"');
+  });
+
+  test('filter uses CLOSED_STATUSES.has() to exclude closed slices', () => {
+    assert.match(source, /CLOSED_STATUSES\.has\(s\.status\)/,
+      'filter should call CLOSED_STATUSES.has(s.status)');
+  });
+
+  test('findMissingSummaries function exists', () => {
+    assert.match(source, /function findMissingSummaries\(/,
+      'findMissingSummaries function should be defined');
+  });
+
+  test('filter is negated (excludes closed, keeps open)', () => {
+    // The filter should use !CLOSED_STATUSES.has() to exclude closed slices
+    assert.match(source, /!CLOSED_STATUSES\.has\(s\.status\)/,
+      'filter should negate CLOSED_STATUSES.has() to exclude closed slices');
+  });
+});