A cache forwards a POST to a URI it holds a stored response for, and the origin answers 303 (See Other). What must the cache do with the stored response for the target URI?
Invalidate it only if the response also carries Cache-Control: no-cache
Nothing, because POST responses are not cacheable in the first place
Invalidate it, because 3xx counts as a non-error response to an unsafe method✓Bonne réponse
Nothing; only 2xx responses trigger invalidation
Explication
Invalidation is keyed on an unsafe method plus a non-error status, and the caching spec defines non-error as 2xx or 3xx, so a redirect invalidates just as a 200 would. Whether the POST response itself was cacheable is a separate question from whether it invalidates the stored entry.