Adds Discord direct messages as a notification channel. Users link their
Discord account via OAuth2 (identify scope only, one-time server-side
state rows); a bot delivers their inbox notifications as DMs.
- Extract the email channel's watermark sweep into a generic
account-channel engine; email and Discord are now thin adapters, so
the SKIP LOCKED claim / watermark-after-send durability logic exists
once.
- New internal/discord REST client (token exchange, identity, open DM,
send message) — no Gateway connection, no new dependencies.
- Opt-in master switch (notifications.discord_enabled, default off)
gates delivery, linking, capability, and the admin settings reveal.
- Admin UI: credentials (secret + bot token encrypted at rest), dev
portal setup checklist, bot invite link buttons, and a test button
that bypasses the settings read cache and is disabled while
credential edits are unsaved.
- DM failures from missing shared guild (Discord 50007) surface as link
health in user settings and self-heal via capped backoff.
- New combined mode (per_episode_and_digest) for email and Discord:
instant sends all day plus a daily digest recapping the whole window
since the previous digest.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
