Counter-announce to non-leader peers to speed up connectivity

[rogersanick]

Faster discovery by counter-announcing

To prevent race conditions when exchanging WebRTC SDP offers, we compare peer IDs. The lower-ID peer always leads by creating the offer.

const shouldLeadOffer = selfId < peerId

...

if (!shouldLeadOffer && !announcePeerState.offerPeer) {
  return
}

This means that when a new lower ID peer joins and announces, the higher ID peer silently ignores. The new joining peer must then wait up to ~5.3 seconds for the higher ID peer's next re-announce before a negotiation for connectivity begins.

This change makes the higher ID peer immediately counter-announce to the lower ID peer's self topic, allowing the connection to begin right away.

Changes

• packages/core/src/signal-handler.ts — In the !shouldLeadOffer branch, reply with {peerId: selfId} to the announcing peer's self topic instead of returning silently.
• test/node/shared-room-peer-reuse.spec.ts — Two new test cases: higher-ID peer replies to lower-ID peer; lower-ID peer does not reply (it leads the offer instead).

[dmotz]

Thanks! Did some testing and saw this drop the connection time for peers coming later, which is something that's not measured in the existing tests. Will publish this in the next release.