[BWS, BWC] TSS - add copayerReady event

[gabrielbazan7]

Description

Adds a copayerReady event to TssSign (BWC) so callers can track which copayers have joined a signing session in real time.

Changelog

• BWC — TssSign now emits a copayerReady event with the copayer's ID when a participant joins a signing session. Self is emitted immediately on start(); remote participants are emitted during subscribe() once round 0 is complete.
• BWS — GET /v1/tss/sign/:id/:round now includes a participants field (array of copayer IDs) in its response when a round is complete.
• Tests

Testing Notes

Add any helpful notes for reviewers to test your code here.

---

Checklist

• I have read CONTRIBUTING.md and verified that this PR follows the guidelines and requirements outlined in it.

[kajoseph]

Are you wanting the participants to be returned to the client in real time? Currently, this logic is only hit once all participants have joined (per line 300: if (otherPartyMsgs.length === session.m - 1)). If you want it to be real time, we should move this new logic to be between lines 299-300 and then return participants in the returned object on line 311 (after the if block) as well.

[kajoseph]

If we change it as noted above, then the client will just need to be aware that the copayerReady event will fire duplicates.

[gabrielbazan7]

Hey, yes thanks. I moved that logic outside of the if. I also added an emittedParticipants array to avoid duplicates on the client side. In any case, this shouldn’t cause any issues in the app, since it’s just used to show a checkmark next to the copayer’s name in the UI.

[kajoseph]

Good work!