* feat: shorten every recipient unsubscribe link from a 96-character signed token to a 22-character stored ticket carrying 128 bits from crypto/rand, minted once per recipient per campaign and reused by every step, so the address the text/plain half of a cold email prints in full fits on one line and cannot be guessed, keeping the signed form working for links already in inboxes and as the fallback when the store cannot be written, and answering a failed lookup with a retryable 'try again shortly' instead of telling the recipient their opt-out is invalid (issue #498)
* fix: restore the disabled-signer guard in URLOn, which factoring the URL builder moved behind a token mint that dereferences the signing key, so a nil or origin-less signer returns the empty string every caller reads as 'no link can be minted' instead of panicking (PR #525 review)
Matthew Meszaros