Add configurable notifications via Slack

[dividing-by-zaro]

Overview

Add a notification system that alerts users when significant changes occur in their tracked repositories. Notifications should be real-time for major/breaking changes and digest-style for minor updates.

Goals

• Keep users informed about important repo changes without requiring them to check the feed
• Provide flexibility in how and when users receive notifications
• Support both email and Slack (webhook) as notification channels

Features

Notification Triggers

• Immediate notifications for:
  • Major/breaking changes (significance: major)
  • Security updates
  • New releases
• Digest notifications (daily/weekly configurable) for:
  • Minor and patch updates
  • Feature additions and enhancements
  • Bug fixes

Email Notifications

• Beautiful HTML email templates matching the app's neo-brutalist design
• Configurable frequency: immediate (for major), daily digest, weekly digest, or off
• Unsubscribe link in every email
• Email verification before enabling

Slack Integration (Webhook)

• Users provide a Slack webhook URL
• Posts formatted messages to the configured channel
• Rich message formatting with:
  • Repo name and update summary
  • Significance level indicator
  • Link back to the update in the app
  • Category badges

User Settings

• Global notification preferences (default for all repos)
• Per-repo overrides (e.g., turn off notifications for a specific repo)
• Channel selection (email, Slack, or both)
• Quiet hours / timezone awareness

Technical Considerations

• Queue-based notification processing (avoid blocking the main app)
• Rate limiting for external API calls (Slack, email provider)
• Batch digest emails efficiently
• Store notification preferences in User and UserRepo tables
• Track notification history for debugging/user reference

Out of Scope (for now)

• Full Slack app with interactive commands
• Mobile push notifications
• In-app notification center

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Implementation Plan: Slack Integration (Phase 1)

Slack webhooks are simpler to implement than email (no deliverability concerns, no third-party service setup, no HTML email formatting). Recommended as the first notification channel.

1. Database Changes

• Add slackWebhookUrl to User table
• Add notifyOnMajor, notifyOnRelease boolean fields
• Prisma migration

2. API Endpoints

• PUT /api/user/notifications - save preferences
• POST /api/user/notifications/test - send test message to verify webhook

3. Slack Service (server/src/services/slack.ts)

• sendUpdate(webhookUrl, update) - format and POST
• sendRelease(webhookUrl, release) - format and POST
• Block Kit message formatting for rich messages

4. Notification Triggers

• Hook into existing classification pipeline
• After new major update indexed → queue notification
• After new release indexed → queue notification

5. Settings UI

• Webhook URL input field
• Toggle switches for notification types
• "Send test" button to verify configuration

6. Rate Limiting / Error Handling

• Don't spam on bulk indexing (initial repo add, sweeps)
• Handle webhook URL invalidation gracefully
• Batch notifications during sweep runs

Complexity Notes

The Slack service itself is straightforward. The main complexity is deciding when to trigger notifications:

• Avoid spam during initial repo indexing
• Batch during daily sweep runs
• Handle invalid/revoked webhook URLs