This is why unit tests before e2e tests.
It's higher risk to build on components without unit tests test coverage, even if the paltry smoke/e2e tests say it's fine per the customer's input examples.
Is it better to fuzz low-level components or high-level user-facing interfaces first?
IIUC in relation to Formal Methods, tests and test coverage are not sufficient but are advisable.
Competency Story: The customer and product owner can write BDD tests in order to validate the app against the requirements
Prompt: Write playwright tests for #token_reference, that run a named factored-out login sequence, and then test as human user would that: when you click on Home that it navigates to / (given browser MCP and recently the Gemini 2.5 Computer Operator model)