- SessionSchedulerService now backs off for 15 minutes after any
handler failure (confirmation, one-hour reminder, join link),
preventing infinite retry loops on Discord 403 Missing Access.
- Added per-session ConcurrentDictionary backoff tracking with
automatic cleanup on success.
- Enhanced DiscordPlatformMessenger logging for SendConfirmation
and SendJoinLink to aid permission diagnostics.
- Added 3 regression tests for backoff behavior.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Toutsu