Makes external email actually leave the building (was sandbox-only). SmtpProvider
implements CapabilityProvider; env-activated (accounts@ primary, ceo@ fallback);
transporter injected for tests.
- send() maps target+payload -> {from,to,subject,html,text,inReplyTo,references};
providerRef = nodemailer's real Message-ID (so replies thread via In-Reply-To).
- Fallback ONLY on pre-acceptance failures (connect/auth/timeout) — a post-acceptance
error is terminal, so a message the server already took can't be double-delivered.
- Never throws — transport failure -> FAILED, per the adapter doctrine.
- Registry precedence via registration order: SMTP > HTTP relay > sandbox for EMAIL.
Verified: 13 unit tests (config/envelope/fallback/precedence) + a REAL SMTP round-trip
against nodemailer Ethereal (SENT, genuine Message-ID). Full suite 281/281, boundary+build clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
maaz519
74cca2d534