Pure functions for IMAP message parsing and filtering.
No I/O, no side effects.

Pure functions for SMTP email preparation and validation.
No I/O, no side effects.

Pure functions for Twilio API data transformation.
No I/O, no side effects.

Protocol definitions for external service adapters.

Defines three integration protocols:
- ISmtpProvider    — outbound email via SMTP
- IImapMailbox     — inbound email via IMAP
- ITwilioMessaging — Twilio SMS and WhatsApp messaging

Malli validation schemas for external service adapters.

IMAP mailbox adapter implementing IImapMailbox.

Uses javax.mail for IMAP access. Connections are opened per-call and closed
in a finally block. IMAP UIDs are accessed by casting the Folder to IMAPFolder.

Usage:
  (def mailbox (create-imap-mailbox
                 {:host "imap.gmail.com"
                  :port 993
                  :username "user@gmail.com"
                  :password "app-password"
                  :ssl? true}))
  (fetch-unread! mailbox)

SMTP transport adapter implementing ISmtpProvider.

Uses javax.mail for SMTP communication. This adapter is positioned as a
transport-level provider — independent of the email lib's higher-level
abstraction (templating, job queuing, etc.).

Usage:
  (def provider (create-smtp-provider
                  {:host "smtp.gmail.com"
                   :port 587
                   :username "user@gmail.com"
                   :password "app-password"
                   :tls? true
                   :from "no-reply@example.com"}))
  (send-email! provider {:to "recipient@example.com"
                         :subject "Hello"
                         :body "World"})

Twilio messaging adapter implementing ITwilioMessaging.

Uses clj-http with Basic auth (account-sid + auth-token).
SMS and WhatsApp share the same Messages endpoint; the only difference
is the whatsapp: prefix added by core/twilio.

Usage:
  (def twilio (create-twilio-adapter
                {:account-sid "ACxxx"
                 :auth-token  "token"
                 :from-number "+15005550006"}))
  (send-sms! twilio {:to "+31612345678" :body "Hello!"})

Integrant lifecycle wiring for the external service adapters.

Registers init-key and halt-key! multimethods for:
  :boundary.external/smtp   — SMTP transport provider
  :boundary.external/imap   — IMAP mailbox reader
  :boundary.external/twilio — Twilio SMS / WhatsApp

All three keys are opt-in: add them to :active in config.edn to enable.
They are shipped in :inactive by default.