diff --git a/crates/manager-core/migrations/0038_email_realtime_secret_check.sql b/crates/manager-core/migrations/0038_email_realtime_secret_check.sql
new file mode 100644
index 0000000..7d0096f
--- /dev/null
+++ b/crates/manager-core/migrations/0038_email_realtime_secret_check.sql
@@ -0,0 +1,19 @@
+-- F-M-002 (audit 2026-06-07): coupled-nullness CHECK constraints on
+-- (encrypted, nonce) pairs.
+--
+-- The current schema has each column nullable independently:
+--   email_trigger_details.inbound_secret_encrypted / _nonce
+--   app_secrets.realtime_signing_key_encrypted / _nonce
+--
+-- A bug or partial write could leave one populated and the other NULL
+-- — silently bypassing signature verification (receiver decrypts only
+-- if the encrypted column is set). Defend with a coupled-nullness
+-- CHECK on each pair so a partial state is rejected at the DB
+-- boundary.
+ALTER TABLE email_trigger_details
+    ADD CONSTRAINT email_trigger_details_inbound_secret_pair
+    CHECK ((inbound_secret_encrypted IS NULL) = (inbound_secret_nonce IS NULL));
+
+ALTER TABLE app_secrets
+    ADD CONSTRAINT app_secrets_realtime_signing_key_pair
+    CHECK ((realtime_signing_key_encrypted IS NULL) = (realtime_signing_key_nonce IS NULL));