fix: bound the peer relay connection cache with LRU eviction - #207
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RemoteManager cached one connection per (url, addr) peer and only ever dropped an entry when that connection died, so a relay that talks to many peers over its lifetime accumulated pooled QUIC connections without limit — each with its own keep-alive — for the life of the process. Give the pool a configurable capacity (RelayTuning::max_remote_connections, default 256, 0 disables) with least-recently-used eviction. Recency is refreshed on cache hits as well as insertion, and eviction only reclaims entries nothing is using: a subscriber holds a use guard for as long as its upstream subscription lives, and an entry with a live guard — or whose slot lock is held by an in-flight connect or teardown — is skipped rather than closed, so the pool may sit over capacity instead of cutting off a live subscription. Candidate slots are probed with try_lock while the pool lock is held, so the existing pool/slot lock order is unchanged and no lock is held across an await.
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Backport of #202 to draft-14. On this branch the knob rides the existing
RelayTuning, so no public signature changes.RemoteManagerkeeps one cached connection per(url, addr)peer and only drops an entry when that connection dies, so a relay that talks to many peers over its lifetime accumulates pooled QUIC connections without limit, each with its own keep-alive, for the life of the process. This adds a configurable capacity (default 256,0disables) with least-recently-used eviction, refreshing recency on cache hits as well as insertions. Eviction only reclaims connections that nothing is using — every caller holds a use guard while it is subscribed, publishing or forwarding over a connection, and an entry with a live guard (or a slot lock held by an in-flight connect) is skipped rather than closed, so a full pool of busy peers stays over capacity instead of cutting off a live subscription. No new dependencies; the LRU is a linear scan over a few hundred entries, run only when a new connection is added.