My restored Cypress session was lying to me

Author's Note / Disclosure: 100% human-authored content based on real production engineering work. No AI was involved in writing the article, technical analysis, or code. cy.session() is the single biggest speed win available to an authenticated Cypress suite. You log in once, Cypress snapshots cookies, localStorage and sessionStorage , and every later spec restores that snapshot instead of walking through an identity provider. The safety net is validate() . Cypress runs it after restoring a cached session; if it throws, fails an assertion, or yields false , Cypress throws the snapshot away and runs setup again. That is the whole contract: a bad session gets detected and replaced. Mine could not fail. For weeks. And it cost me days of chasing "flaky" specs that were nothing of the kind. The code that looked fine Cypress . Commands . add ( ' login ' , ( user : User ) => { cy . session ( user . username , () => { cy . visit ( ' / ' ) cy . origin ( idpOrigin , { args : user }, ({ username , password }) => { cy . get ( ' #username ' ). type ( username ) cy . get ( ' #password ' ). type ( password , { log : false }) cy . get ( ' button[type="submit"] ' ). click () }) cy . get ( ' #app-shell ' ). should ( ' be.visible ' ) }, { cacheAcrossSpecs : true , validate () { cy . request ( ' /connect/userinfo ' ). its ( ' status ' ). should ( ' eq ' , 200 ) }, }, ) }) Reasonable, right? /connect/userinfo is the OIDC user info endpoint. If the session is dead it should 401, validate() fails, and we log in again. Why it always passes Two independent bugs stack up here, and either one alone is enough to make the check worthless. The URL is relative. cy.request('/connect/userinfo') resolves against baseUrl , which is the application, not the identity provider. So the request never touches the IdP. The application is a single-page app. Its host serves index.html for any path it does not recognise, because that is what history-API routing requires. A request for /connect/userinfo gets b