Restore relay work for draft-18 and port missing session layer - #211
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The draft-18 integration resolved moq-relay-ietf and its siblings in favour of the draft-18 side, which dropped the relay work main had accumulated: track lookup through the coordinator, the PUBLISH_NAMESPACE fan-out to peer relays, the namespace and track change broadcasts, the pull-through cache and the upstream namespace manager. Without those a relay cannot route between hosts at track granularity, which the draft-16 line has done for a while. That merge recorded the port as deferred rather than unwanted. The crates come back from main unchanged, and the commit that follows adapts the session layer they call to draft-18 rather than reinventing the relay on top of it. Restoring wholesale would have reverted draft-18's ALPN version negotiation, so that is reapplied: the server offers every supported version and rejects a client that offers none, instead of accepting with no protocol and failing later at SETUP. This commit does not build alone.
…raft-18 The restored relay calls session APIs that landed on main after the draft-18 fork, so draft-18 never had them: SUBSCRIBE_NAMESPACE and direct PUBLISH in both directions, and SessionConfig with its connect and accept constructors. Adapted rather than copied. Each request owns a bidirectional stream and its responses omit the Request ID, so responses go through the bidi response paths. SUBSCRIBE_NAMESPACE sits outside the generic response map because NAMESPACE carries no Request ID to route on. The object-sending loop is shared between SUBSCRIBE and PUBLISH as ObjectForwarder. PUBLISH is accepted with REQUEST_OK, since draft-18 removed the dedicated PUBLISH_OK type; the old type is still accepted on receive. A protocol violation closes the session rather than being logged and discarded, and a track alias reused while live closes with DUPLICATE_TRACK_ALIAS. PUBLISH_DONE carries the real number of streams opened, which is what tells a subscriber whether it can discard state. pending_requests.rs is not ported. Its response routing is structural once each request owns a stream, and its outbound timeout would have covered PUBLISH alone while subscribe_open has never had one, so Published::publish documents that ok() is unbounded and leaves the limit to the caller. Interop cases in moq-test-client cover both new directions against a local relay.
State::lock and lock_mut unwrapped the inner mutex, so one panic while holding a state made every later access to it panic too. One State backs every subscription, reader and waiter built on it, so a single failed request could take the rest down with it. Both accessors now recover the guard, log once and clear the poison flag. The state can hold a half-finished update, which is what the log is for. try_lock and try_lock_mut still report poisoning, for callers that would rather decide. The drop path was worse: on a poisoned lock it returned before notify(), leaving every task awaiting that state waiting for a change that could never arrive. The unwraps are the same on main, so this applies there unchanged. Tests poison a state from a thread that panics under the lock, then assert access still works and that a later drop wakes a waiter. The waiter case panics holding a shared ref rather than a mutable one, because StateMut notifies as it unwinds and would make the test pass either way.
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The draft-18-dev branch got mangled and only contained wire format changes, so this restores the other relay changes from main ~identically, apart from reapplying draft-18's ALPN negotiation. This also ports the session APIs they call, which landed on main after the fork: SUBSCRIBE_NAMESPACE, direct PUBLISH and SessionConfig, adapted to one bidi stream per request. The last change also stops State::lock unwrapping a poisoned mutex, so one panic no longer spreads to every later access of that state.