Add LitePub relay implementation

[sij411]

Summary

This PR adds a LitePub-compatible ActivityPub relay implementation to the
@fedify/relay package, complementing the existing Mastodon relay implementation.

Related Issue

#359

Changes

• Added LitePubRelay class in packages/relay/src/relay.ts:321-585 that implements
  the LitePub relay protocol
• Implemented LitePub-specific activity handling:
  • Wraps incoming Create, Update, Move, and Delete activities in Announce
    activities before forwarding
  • Uses Application actor type instead of Mastodon's Service type
  • Sends announcements to PUBLIC_COLLECTION for broader visibility
• Added comprehensive test suite for LitePubRelay in
  packages/relay/src/relay.test.ts:455-832 covering:
  • Relay initialization and configuration
  • Actor endpoint behavior (Application type)
  • Followers collection management
  • Subscription handler integration
  • Follow/Undo activity processing
  • Multiple follower support

Benefits

• Protocol compatibility: Enables Fedify relay instances to work with
  LitePub-compatible fediverse software, which expects activities to be wrapped in
  Announce rather than directly forwarded
• Broader reach: Using PUBLIC_COLLECTION as the audience for announces ensures
  better visibility across the fediverse
• Developer choice: Developers can now choose between Mastodon-style
  (MastodonRelay) and LitePub-style (LitePubRelay) relay implementations based on
  their target ecosystem
• Consistent API: Both relay implementations share the same Relay interface, making
  it easy to switch between protocols

Checklist

• Did you add a changelog entry to the CHANGES.md?
• Did you write some relevant docs about this change (if it's a new feature)?
• Did you write a regression test to reproduce the bug (if it's a bug fix)?
• Did you write some tests for this change (if it's a new feature)?
• Did you run deno task test-all on your machine?

Additional Notes

Key differences between LitePub and Mastodon relay protocols:

1. Actor type: LitePub uses Application, Mastodon uses Service
2. Activity forwarding:
   - LitePub wraps activities in Announce objects with relay as actor
   - Mastodon forwards activities directly using ctx.forwardActivity()
3. Audience: LitePub sends to PUBLIC_COLLECTION for maximum visibility

The implementation follows the same subscription management and key pair handling
as MastodonRelay, ensuring consistent behavior for core relay functionality like
follower management and subscription approvals.

[codecov]

Codecov Report

❌ Patch coverage is 47.09898% with 155 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
packages/relay/src/relay.ts	47.09%	155 Missing ⚠️

Files with missing lines	Coverage Δ
packages/relay/src/relay.ts	54.28% <47.09%> (-8.79%)	⬇️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[dahlia]

@sij411 Could you rebase your commits on the latest next branch?

[dahlia]

@sij411 I fixed several packaging issues for @fedify/relay in the last commit (c31cc63) of the next branch. Could you rebase your commits on it once again?

[dahlia]

It looks like there's quite a bit of duplicate code between MastodonRelay and LitePubRelay. How about we create an abstract base class, let's call it BaseRelay for now, move the shared code into it, and then have MastodonRelay and LitePubRelay inherit from BaseRelay?

[github-actions]

The docs for this pull request have been published:

https://7c0acbfa.fedify.pages.dev

[sij411]

It looks like there's quite a bit of duplicate code between MastodonRelay and LitePubRelay. How about we create an abstract base class, let's call it BaseRelay for now, move the shared code into it, and then have MastodonRelay and LitePubRelay inherit from BaseRelay?

That was my original plan, yes it is supposed be like that eventually. Do you think that should be done in this PR?

[dahlia]

@sij411 Fair enough. Please refactor it in the next PR!

[dahlia]

By the way, LitePubRelay should be tested with actual Pleroma/Akkoma instances.

[sij411]

By the way, LitePubRelay should be tested with actual Pleroma/Akkoma instances.

I'll let you know test result when it's done. maybe in few days.

[sij411]

As you know, we tested LitePub relay and checked 1) the relay server can be subscribed by two Akkoma instances (deployed with DigitalOcean Droplet), 2) the posts of relay subscribers are showed up on "Known Hosts" tab for each instance.

I think we could wrap up the LitePub relay protocol implementations, and refactor module structures and etc in another PR.

[github-actions]

The latest push to this pull request has been published to JSR and npm as a pre-release:

Package	Version	JSR	npm
@fedify/fedify	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/cli	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/amqp	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/cfworkers	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/denokv	2.0.0-pr.471.1924+020b6605	JSR
@fedify/elysia	2.0.0-pr.471.1924+020b6605		npm
@fedify/express	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/h3	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/hono	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/koa	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/nestjs	2.0.0-pr.471.1924+020b6605		npm
@fedify/next	2.0.0-pr.471.1924+020b6605		npm
@fedify/postgres	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/redis	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/sqlite	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/sveltekit	2.0.0-pr.471.1924+020b6605	JSR	npm
@fedify/testing	2.0.0-pr.471.1924+020b6605	JSR	npm