navigator.cookieEnabled agrees with whether a cookie can actually be stored

navigator.cookieEnabled is a claim; writing a cookie and reading it back is a measurement. They are supposed to be two views of one fact, which makes the disagreement a free coherence check requiring no reference value and no knowledge of the host. The reason it earns a row of its own is that the failure has a consequence far beyond fingerprinting.

A de-Googled or privacy-hardened Chromium base can ship cookie restrictions the boolean does not reflect, and a stealth browser built on such a base traced a total, unexplained failure of reCAPTCHA v3 tokens to exactly this: the reputation cookie those challenges depend on could never be stored, so every token scored as a stranger. Nothing in a fingerprint report points at that.

The browser looks coherent, the identity looks plausible, and the challenge fails anyway — which is the most expensive class of bug in this field, because it sends people hunting through canvas noise for a problem that lives in the cookie jar. The probe writes a first-party cookie and removes it immediately, so it leaves no state behind.