Most developers test error messages visually. If the red border appears and the message shows up, the job's done. But WCAG 4.1.3 asks a different question: does this change reach assistive technology?
What is a status message
A status message is any change in content that isn't triggered by user focus — errors, confirmations, loading states. If it isn't announced, it doesn't exist for screen reader users.
The fix
The fix is not complicated. Adding role="alert" to the error container adds an implicit aria-live="assertive" to the element. Any content injected into it will be read immediately by screen readers.
Why most developers miss it
Because it works visually. The red border, the message — all visible. The disconnect only shows up when you turn on a screen reader.
This is why accessibility testing cannot be visual only.