Goal

Ship HITL (human-in-the-loop) requests to a Slack channel or DM the same way we ship them to Telegram today. Inline approve/decline buttons via Slack Block Kit.

Background

Notification channels are abstracted behind NotificationChannelAdapter (src/server/services/channels/types.ts). Telegram is the only implementation today. Each channel has:

• An adapter (send, isConfigured, optional webhook handler)
• Credential storage in notification_channels.credential_ciphertext (encrypted per-channel)
• A UI panel in Settings that enrolls + tests the channel

Where to start

• Read src/server/services/channels/telegram.ts and telegram-credentials.ts as your reference.
• Create src/server/services/channels/slack.ts with:
  • slackAdapter implementing NotificationChannelAdapter — formats the HITL proposal into Slack Block Kit with Approve / Decline buttons
  • Uses Slack's Incoming Webhooks for sending, or the Web API if a bot token is configured
• Webhook handler for interactive components (button presses) — POST to /api/v1/channels/slack/webhook with Slack signing-secret verification.
• Register "slack" in NotificationChannelKind (src/server/services/channels/types.ts) and the adapter registry (registry.ts).
• UI: build src/web/components/settings/SlackChannelPanel.tsx modeled on TelegramChannelPanel.tsx.

Acceptance criteria

• Admin can paste a Slack Incoming Webhook URL or Bot Token in Settings and "Test send" works.
• A HITL proposal delivered to Slack shows Approve / Decline buttons that resolve the proposal when tapped (same behavior as Telegram).
• Signing secret verification on the interactive-components webhook (don't trust Slack's body without it).
• Unit tests for signature verification + block kit formatting.