fix: keep one active email OTP per account

frontend/db/migrations/20260810024500_unique_verification_identifiers.sql

@@ -0,0 +1,18 @@
+lock table identity.verifications in share row exclusive mode;
+
+with ranked as (
+  select
+    id,
+    row_number() over (
+      partition by identifier
+      order by created_at desc, id desc
+    ) as position
+  from identity.verifications
+)
+delete from identity.verifications verification
+using ranked
+where verification.id = ranked.id
+  and ranked.position > 1;
+
+create unique index if not exists identity_verifications_identifier_key
+  on identity.verifications (identifier);

frontend/tests/database-self-hosted-identity.test.ts

@@ -18,6 +18,12 @@ const identityMigration = fileURLToPath(
     import.meta.url,
   ),
 );
+const uniqueVerificationMigration = fileURLToPath(
+  new URL(
+    "../db/migrations/20260810024500_unique_verification_identifiers.sql",
+    import.meta.url,
+  ),
+);
 
 test("self-hosted identity migration creates Better Auth tables with least privilege", () => {
   const migrationSource = readFileSync(identityMigration, "utf8");
@@ -225,6 +231,29 @@ test("self-hosted identity migration creates Better Auth tables with least privi
       ),
       "1",
     );
+
+    fixture.psql("drop index identity.identity_verifications_identifier_key");
+    fixture.psql(`
+      insert into identity.verifications (identifier, value, expires_at, created_at)
+      values
+        ('sign-in-otp-owner@example.com', 'older', now() + interval '5 minutes', now() - interval '1 second'),
+        ('sign-in-otp-owner@example.com', 'newer', now() + interval '5 minutes', now())
+    `);
+    fixture.psql(readFileSync(uniqueVerificationMigration, "utf8"));
+    assert.equal(
+      fixture.psql(`
+        select value
+        from identity.verifications
+        where identifier = 'sign-in-otp-owner@example.com'
+      `),
+      "newer",
+    );
+    assert.throws(() =>
+      fixture.psql(`
+        insert into identity.verifications (identifier, value, expires_at)
+        values ('sign-in-otp-owner@example.com', 'duplicate', now() + interval '5 minutes')
+      `),
+    );
   } finally {
     fixture.stop();
   }

frontend/tests/identity-auth-integration.test.ts

@@ -204,6 +204,37 @@ test("Better Auth supports shared user OTP/password sessions for admins", async
     );
     assert.equal(unauthenticatedSet.status, 401);
 
+    const rotatedEmail = "rotated-otp@example.com";
+    for (let attempt = 0; attempt < 2; attempt += 1) {
+      const send = await handlers.POST(
+        request(userHost, "/api/auth/email-otp/send-verification-otp", {
+          email: rotatedEmail,
+          type: "sign-in",
+        }),
+      );
+      assert.equal(send.status, 200);
+    }
+    const rotatedMessage = sender.messages.at(-1);
+    assert.equal(
+      fixture.psql(`
+        select count(*)
+        from identity.verifications
+        where identifier = 'sign-in-otp-${rotatedEmail}'
+      `),
+      "1",
+    );
+    assert.equal(
+      (
+        await handlers.POST(
+          request(userHost, "/api/auth/sign-in/email-otp", {
+            email: rotatedEmail,
+            otp: rotatedMessage?.otp,
+          }),
+        )
+      ).status,
+      200,
+    );
+
     const newEmail = "new-user@example.com";
     const firstPassword = "first-password";
     const resetPassword = "reset-password";