Gate r2 finding 2 (same class as the webhook blank-secret fix):
TWILIO_AUTH_TOKEN was read unstripped, so a whitespace-only token
passed check_sms_requirements and keyed the X-Twilio-Signature HMAC
with blanks, letting anyone forge inbound SMS. Strip the token at
every read (adapter init, standalone send, requirements check).
Stripping alone would leave an empty key, and HMAC with an empty key
is equally public (verified by probe: a signature forged with b''
was accepted). So _check_signature now refuses outright when no
auth token is set. This goes one line past the reviewer's FIX, which
only asked for the strip.
84cb790e64