Add interruption_scope_id to ChannelMessage for thread-aware cancellation. Slack genuine thread replies and Matrix threads get scoped keys, preventing cross-thread cancellation. All other channels preserve existing behavior.
Supersedes #3900. Depends on #3891.
* feat(channels): add Reddit, Bluesky, and generic Webhook adapters
- Reddit: OAuth2 polling for mentions/DMs/replies, comment and DM sending
- Bluesky: AT Protocol session auth, notification polling, post replies
- Webhook: Axum HTTP server for inbound, configurable outbound POST/PUT
- All three follow existing channel patterns with tests
* fix(channels): use neutral test fixtures and improve test naming in webhook
Argenis
Giulio V