diff --git a/src/resources/extensions/gsd/tests/defer-milestone-stamp.test.ts b/src/resources/extensions/gsd/tests/defer-milestone-stamp.test.ts
new file mode 100644
index 000000000..d60cbafcc
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/defer-milestone-stamp.test.ts
@@ -0,0 +1,34 @@
+/**
+ * Regression test for #3542: defer and milestone captures must be stamped
+ * as executed after triage resolution, regardless of directory state.
+ */
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { mkdtempSync, mkdirSync, writeFileSync, readFileSync, rmSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { executeTriageResolutions } from "../triage-resolution.ts";
+import { appendCapture, markCaptureResolved, loadAllCaptures } from "../captures.ts";
+
+test("defer captures without milestone ID are stamped as executed (#3542)", async () => {
+  const base = mkdtempSync(join(tmpdir(), "gsd-stamp-"));
+  mkdirSync(join(base, ".gsd", "milestones", "M001"), { recursive: true });
+  try {
+    appendCapture(base, "Improve error messages");
+    const captures = loadAllCaptures(base);
+    const id = captures[0].id;
+    markCaptureResolved(base, id, {
+      classification: "defer",
+      resolution: "Deferred to a future UX-polish milestone",
+      reason: "Not urgent",
+    });
+
+    executeTriageResolutions(base, "M001", "S01");
+
+    const after = loadAllCaptures(base);
+    const cap = after.find(c => c.id === id);
+    assert.ok(cap?.executed, "Defer capture should be stamped as executed");
+  } finally {
+    rmSync(base, { recursive: true, force: true });
+  }
+});