diff --git a/DEFERRED_SECURITY.md b/DEFERRED_SECURITY.md
index 0321d1a..a933937 100644
--- a/DEFERRED_SECURITY.md
+++ b/DEFERRED_SECURITY.md
@@ -11,7 +11,19 @@ These items were identified during a security review on 2026-05-02 and conscious
 
 `sessionId` and `sessionKey` are currently read from query parameters, which means they appear in server access logs, browser history, proxy logs, and `Referer` headers.
 
-**Fix:** Move to request headers (`X-Session-Id` / `X-Session-Key`) or the request body. Requires a corresponding frontend update.
+**Fix (updated 2026-09-06):** Move the calendar onto the shared admin identity -
+`requireAppAccess('calendar')` against the better-auth session cookie, per
+`docs/calendar-auth-migration.md`. That closes this item outright rather than moving the
+credential to a safer place, and it is now the cheaper of the two: the feedback and tickets
+modules made the same move on 2026-09-06 for one line each.
+
+~~Move to request headers (`X-Session-Id` / `X-Session-Key`) or the request body.~~ No longer
+the recommendation. Nothing on the server reads those two headers any more - the calendar's
+query parameters are the last legacy credential path in the API - so this would build a second
+mechanism just as the first is being retired. They survive only in the CORS `allowedHeaders`
+list, and only until both frontends are redeployed.
+
+Either fix requires a corresponding frontend update.
 
 > Note: the shared calendar `password` parameter in query params is intentional (iCal clients don't support headers) and is acceptable for the current setup.
 
diff --git a/test/admin/auth-binding.ts b/test/admin/auth-binding.ts
index 21b00b2..d50a0c9 100644
--- a/test/admin/auth-binding.ts
+++ b/test/admin/auth-binding.ts
@@ -102,6 +102,11 @@ export const describeAdminBinding = (
 			expect(res.locals.admin).toMatchObject({id: 'u1', email: 'a@nachklang.art', displayName: 'Anna Admin'});
 		});
 
+		// Weaker than it looks and kept deliberately: neither module imports
+		// checkSession any more, so this cannot fail today. It is a tripwire for
+		// the change that would matter - someone reintroducing a header-session
+		// fallback "just for the calendar users who have not been invited yet",
+		// which is exactly the shortcut the cutover exists to close.
 		it('never falls back to a calendar header session', async () => {
 			m.getSession.mockResolvedValue(null);