feat: Add Bluesky support

[andrewgazelka]

Summary

Add support for posting to Bluesky via the AT Protocol.

API Research

Official API available - Bluesky is built on the AT Protocol which has a public, well-documented API.

Authentication

• App Passwords: Create in Settings → App Passwords (recommended for CLI tools)
• OAuth2 also supported
• Endpoint: com.atproto.server.createSession returns access/refresh tokens

Creating Posts

Endpoint: com.atproto.repo.createRecord
Collection: app.bsky.feed.post

Rate Limits

• 5,000 points per 5 minutes (sliding window)
• Post creation: 3 points per request
• Reads: 1 point per request
• Headers: RateLimit-Limit, RateLimit-Remaining, RateLimit-Reset

Rust Libraries

atrium-api (v0.24.6) - Primary/official option

• Type-safe AT Protocol bindings
• Handles auth, posts, rich text (mentions, links, hashtags)
• Active development

Proposed CLI

# Authenticate (app password)
post bsky auth --handle user.bsky.social --app-password xxxx-xxxx-xxxx

# Post
post bsky post "Hello Bluesky!"

# Reply to a post
post bsky reply <post-uri> "Your reply"

# Check status
post bsky status

Implementation Notes

• No character limit (unlike X)
• Rich text via facets (mentions, links, hashtags)
• Decentralized - can work with any PDS
• Growing X alternative with developer-friendly approach

References

• AT Protocol Documentation
• Bluesky API Docs
• atrium-api crate