Redesign MRP kick: abort exchange and restart fresh

[Apollon77]

Summary

Replaces the MRP kick mechanism with a cleaner architectural approach:

• Old behavior: Kick short-circuited the MRP retransmission timer on the current exchange, which was fragile due to a race condition where kicks could arrive while a retransmission send was in-flight (timer stopped, isRunning === false).
• New behavior: Kick aborts the current CASE handshake exchange via a localAbort signal and lets connect() loop immediately to a fresh exchange with a clean MRP backoff (~2.25s first retry). DNS-SD address discovery or an explicit peer.kick() now takes effect within seconds instead of waiting out a potentially many-minute backoff.

Key changes

• MessageExchange: Removed exchange.kick() method and the #kick/#kickPending fields entirely — kick logic now lives at the PeerConnection layer
• PeerConnection: Added KickOrigin type ("discover" | "connect"), lastRestartAt shared state, and localAbort-based restart logic in attemptOnce()
• PeerTimingParameters: Added mrpKickRestartIntervalDiscover (30 min) and mrpKickRestartIntervalConnect (10 min) rate-limit thresholds
• Peer: Updated QuietObservable<[KickOrigin]> typing and ConnectionProcess interface to thread origin through

Rate limiting (two layers)

1. QuietObservable (3s debounce, skipSuppressedEmits: true): First-line defense against rapid-fire mDNS churn
2. Per-origin lastRestartAt threshold: Shared across all concurrent address attempts so at most one restart fires per kick

Design notes

• localAbort wraps addressAbort (not overallAbort) — firing it aborts only the current pair() call, not the entire address retry loop
• lastRestartAt is scoped to the PeerConnection call, shared across concurrent address attempts to prevent burst restarts
• If a kick fires just as pair() succeeds, overallAbort() has already fired, making localAbort() harmless

Test plan

• 21 new unit tests in PeerConnectionKickTest.ts covering:
  • PeerTimingParameters defaults and overrides
  • KickOrigin threading through QuietObservable
  • Rate-limiting logic (thresholds, shared state, cross-origin)
  • localAbort restart pattern (abort propagation, loop restart, double-abort safety)
  • Observable type contract (QuietObservable assignability, use() disposal)
• Full protocol test suite passes (607/607, ESM + CJS)
• Type-check clean, linter clean, formatter clean

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes a race in MRP retransmission “kick” handling within MessageExchange so that a kick arriving while a retransmission send is in-flight is not silently dropped, and instead forces the next resubmission to occur immediately.

Changes:

• Add #kickPending to remember kicks that arrive when the retransmission timer isn’t running (send in-flight).
• Clear #kickPending on message boundary (send() finally) and consume it in #initializeResubmission() to start the next timer with zero delay.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

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[lauckhart]

This is getting pretty esoteric :)

Trying to think how we could make these more comprehensible, maybe something like:

retryBackoffResetWindow: {
    connect?: Duration,
    addressChange?: Duration,
}

...but I acknowledge this is no more likely to be understood :)