The relay can charge a few seconds of arithmetic before an account
exists — cheap for one person, expensive for a farm, and unlike a
CAPTCHA it hands nothing to a third party. This is the Android half,
matching the iPhone app.
Asked for only when the relay refuses without one, so a relay with the
feature off — every relay running today — still sees exactly one
request. Rethrown rather than swallowed when this app cannot answer: a
difficulty above the cap leaves it genuinely unable to sign up here, and
"update the app" is then the true sentence.
Two refusals get their own sentences. challenge_required means the app
is behind its server; challenge_failed is nearly always a challenge that
expired while somebody was typing. Sharing one message would send half
these people to the Play Store for nothing. Decided by the relay's code,
never the status, because a 400 is also a bad email.
The bit counting is pinned to exact vectors. A byte-counting
implementation still SATISFIES a 9-bit difficulty — it overshoots to 16
and does 230x the work — so an assertion about "at least 9 leading
zeros" cannot see the bug.
Refs flamenet-relay#39
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
