feat: Experimental Matrix Support + Configuration for Native Rocket.Chat Homeserver Integration

[ShigrafS]

Closes #1029

Description

This PR introduces experimental support for connecting EmbeddedChat directly to a Matrix homeserver, including the new Rocket.Chat native Matrix homeserver (see RocketChat/homeserver).

Key goals achieved:

• EmbeddedChat can now operate in two modes: classic direct Rocket.Chat access (default) or Matrix backend.
• When in Matrix mode, it connects to a configured Matrix homeserver (e.g. the Rocket.Chat native one or any standard homeserver like matrix.org), joins a single room, and supports core send/receive messaging + typing indicators.
• This enables federation benefits across the Matrix network without requiring a full Rocket.Chat backend in many embed scenarios.
• Maintains full backward compatibility with existing Rocket.Chat mode.

This is marked experimental due to partial feature parity (many Rocket.Chat-specific features like edits, deletes, threads, pinning, reactions, search, etc., are stubbed or return "not supported" in Matrix mode). Future iterations can close the gap.

Acceptance Criteria Fulfillment

• Checked out and referenced the Rocket.Chat native Matrix homeserver: https://github.com/RocketChat/homeserver
• Added a configuration option to choose between native Matrix homeserver and direct Rocket.Chat access → new mode prop ('rocketchat' | 'matrix')
• When configured for native Matrix homeserver / Matrix mode: EmbeddedChat can connect to a single configured room, join it (if needed), and send/receive messages successfully → implemented via new MatrixProvider using matrix-js-sdk
• Documentation added explaining how to configure for native Matrix homeserver and switch modes → updated README.md with example JSX + notes on experimental status

Changes Summary

• New mode prop on <EmbeddedChat /> (defaults to 'rocketchat')
  • When mode="matrix", requires host (Matrix homeserver URL) and roomId
• New MatrixProvider class implementing IChatProvider interface (590+ lines)
  • Uses matrix-js-sdk@^39.3.0-rc.0 for client creation, sync, room join, timeline listening, sending messages, typing
  • Maps Matrix events to Rocket.Chat-compatible message format for UI reuse
  • Handles basic login/token flow (reuses @embeddedchat/auth but passes token to Matrix client)
• Extracted IChatProvider interface for clean abstraction between Rocket.Chat and Matrix implementations
• Conditional instantiation in EmbeddedChatApi based on mode
• UI adjustments:
  • Skips optimistic message UI in ChatInput for Matrix mode (relies on real-time timeline events to avoid duplicates)
  • Graceful fallbacks / "not supported" errors for unsupported features (edit/delete/threads/etc.)
• New Storybook story for testing Matrix mode
• Dependency added: matrix-js-sdk@^39.3.0-rc.0
• Documentation: README updated with Matrix mode example + warnings

Limitations (Experimental Phase)

• No support yet for: message editing/deletion, threads, starring/pinning, reactions, file uploads, search, reporting, slash commands, full pagination, E2EE decryption (shows placeholder for encrypted messages)
• Authentication reuses Rocket.Chat-style token flow → best suited for bridged/custom setups or when using Rocket.Chat's native homeserver federation bundle
• Tested primarily with public rooms on matrix.org; Rocket.Chat native homeserver compatibility should be validated in follow-up

How to Test

1. Use the preview deployment after merge/approval: https://rocketchat.github.io/EmbeddedChat/pulls/pr-1030
2. Try classic mode (no mode prop or mode="rocketchat") → should work as before
3. Try Matrix mode:

   <EmbeddedChat
     mode="matrix"
     host="https://matrix.org"           // or your Rocket.Chat native homeserver URL
     roomId="!exampleRoomId:matrix.org"  // replace with real public room ID
     channelName="Matrix Test Room"
   />

[CLAassistant]

All committers have signed the CLA.

[Aryan-Verma-999]

Hi @ShigrafS,

Great to see work continuing on Matrix integration!

Quick question : I see this PR uses matrix-js-sdk@^39.3.0-rc.0. Are you authenticating with Rocket.Chat credentials or Matrix credentials?

The reason I ask is that when I was working on #1030, @Spiral-Memory mentioned we should use Rocket.Chat credentials and integrate with the Rocket.Chat-built homeserver rather than direct Matrix authentication (see #1030 (comment)).

I'm curious how you approached this, did you find a way to use the Matrix SDK while still authenticating through Rocket.Chat? That would be really helpful to understand!

[ShigrafS]

Hi @Aryan-Verma-999 !
Yes, that is exactly the approach I took.

I am authenticating with Rocket.Chat credentials, not Matrix credentials. I refactored the MatrixProvider to use the
RocketChatAuth class first.

The flow is:

• Log in to Rocket.Chat using the provided credentials.
• Retrieve the authToken and userId from the Rocket.Chat session.
• Initialize the matrix-js-sdk client by passing that Rocket.Chat authToken as the Matrix accessToken.

This allows us to keep the authentication native to Rocket.Chat while still leveraging the Matrix SDK for messaging.