diff --git a/packages/api/src/oauth/csrf.spec.ts b/packages/api/src/oauth/csrf.spec.ts
index 143dda61c8..592861d4ed 100644
--- a/packages/api/src/oauth/csrf.spec.ts
+++ b/packages/api/src/oauth/csrf.spec.ts
@@ -241,4 +241,40 @@ describe('setOpenIDMarkerCookies', () => {
       expect.objectContaining({ expires }),
     );
   });
+
+  it('uses integer seconds for fractional refresh expiry durations', () => {
+    const res = { cookie: jest.fn() } as unknown as import('express').Response;
+    const expires = new Date(Date.now() + 604800999);
+
+    setOpenIDMarkerCookies(res, {
+      userId: 'user-123',
+      expires,
+      refreshExpiryMs: 604800999,
+    });
+
+    const signedUserId = (res.cookie as jest.Mock).mock.calls.find(
+      ([name]) => name === OPENID_USER_ID_COOKIE,
+    )?.[1];
+    const payload = jwt.verify(signedUserId, 'marker-secret') as jwt.JwtPayload;
+    if (typeof payload.exp !== 'number' || typeof payload.iat !== 'number') {
+      throw new Error('Expected signed marker JWT to include numeric exp and iat');
+    }
+    expect(payload.exp - payload.iat).toBe(604800);
+  });
+
+  it.each([0, -1000, 999, Number.NaN, Number.POSITIVE_INFINITY])(
+    'throws when the refresh expiry duration is invalid: %p',
+    (refreshExpiryMs) => {
+      const res = { cookie: jest.fn() } as unknown as import('express').Response;
+      const expires = new Date(Date.now() + 999);
+
+      expect(() =>
+        setOpenIDMarkerCookies(res, {
+          userId: 'user-123',
+          expires,
+          refreshExpiryMs,
+        }),
+      ).toThrow('refreshExpiryMs must be a positive duration for OpenID marker cookies');
+    },
+  );
 });
diff --git a/packages/api/src/oauth/csrf.ts b/packages/api/src/oauth/csrf.ts
index ce61882496..e21e587b51 100644
--- a/packages/api/src/oauth/csrf.ts
+++ b/packages/api/src/oauth/csrf.ts
@@ -104,8 +104,13 @@ export function setOpenIDMarkerCookies(
     throw new Error('JWT_REFRESH_SECRET is required for OpenID marker cookies');
   }
 
+  const refreshExpirySeconds = Math.floor(refreshExpiryMs / 1000);
+  if (!Number.isFinite(refreshExpirySeconds) || refreshExpirySeconds <= 0) {
+    throw new Error('refreshExpiryMs must be a positive duration for OpenID marker cookies');
+  }
+
   const signedUserId = jwt.sign({ id: userId }, secret, {
-    expiresIn: refreshExpiryMs / 1000,
+    expiresIn: refreshExpirySeconds,
   });
   res.cookie(OPENID_USER_ID_COOKIE, signedUserId, cookieOptions);
 }
diff --git a/packages/data-schemas/src/methods/refreshTokenBridge.ts b/packages/data-schemas/src/methods/refreshTokenBridge.ts
index 04e1251f6b..b9fbab992a 100644
--- a/packages/data-schemas/src/methods/refreshTokenBridge.ts
+++ b/packages/data-schemas/src/methods/refreshTokenBridge.ts
@@ -1,4 +1,4 @@
-import type { Model } from 'mongoose';
+import type { FilterQuery, Model, UpdateQuery } from 'mongoose';
 import type {
   IRefreshTokenBridge,
   RefreshTokenBridgeCreateData,
@@ -10,7 +10,7 @@ function bridgeFilter({
   oldRefreshTokenHash,
   userId,
   tenantId,
-}: RefreshTokenBridgeQuery): Record<string, unknown> {
+}: RefreshTokenBridgeQuery): FilterQuery<IRefreshTokenBridge> {
   return {
     oldRefreshTokenHash,
     userId,
@@ -30,14 +30,11 @@ export function createRefreshTokenBridgeMethods(mongoose: typeof import('mongoos
     try {
       const RefreshTokenBridge = mongoose.models.RefreshTokenBridge as Model<IRefreshTokenBridge>;
       const filter = bridgeFilter(bridgeData);
-      const update: {
-        $set: Record<string, unknown>;
-        $setOnInsert: Record<string, unknown>;
-        $unset?: Record<string, string>;
-      } = {
+      const update: UpdateQuery<IRefreshTokenBridge> = {
         $set: {
           encryptedNewRefreshToken: bridgeData.encryptedNewRefreshToken,
           expiresAt: bridgeData.expiresAt,
+          ...(bridgeData.openidIssuer != null && { openidIssuer: bridgeData.openidIssuer }),
         },
         $setOnInsert: {
           oldRefreshTokenHash: bridgeData.oldRefreshTokenHash,
@@ -45,12 +42,8 @@ export function createRefreshTokenBridgeMethods(mongoose: typeof import('mongoos
           ...(bridgeData.tenantId != null && { tenantId: bridgeData.tenantId }),
           createdAt: new Date(),
         },
+        ...(bridgeData.openidIssuer == null && { $unset: { openidIssuer: '' } }),
       };
-      if (bridgeData.openidIssuer != null) {
-        update.$set.openidIssuer = bridgeData.openidIssuer;
-      } else {
-        update.$unset = { openidIssuer: '' };
-      }
       return await RefreshTokenBridge.findOneAndUpdate(filter, update, {
         upsert: true,
         new: true,