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WorkerMetadata hashes by uid alone while the generated dataclass equality compares every field, so a pool keyed by the metadata record could not address a worker whose record had changed. Every membership test failed for exactly the events that mattered: the discovery sentinel dropped worker-updated events carrying changed metadata, a worker-dropped event whose record differed from the cached one missed its entry, and a re-announcement inserted a duplicate that consumed a second lease slot. Key the pool by the worker's uid, which is what actually identifies a worker: LoadBalancerContext maps uid to the worker's current record and connection. Membership, lookup, and eviction all follow from the key, so the mutators become single dict operations and a duplicate entry is no longer possible to express. The lease cap counts distinct uids, so a worker re-announcing itself refreshes its entry rather than being turned away at capacity. The upsert flag goes with the old key. Keying by uid gives add_worker and update_worker distinct contracts — add admits or replaces, update refreshes what is already admitted — so the boolean that told them apart has nothing left to select. Connections displaced by a refresh are deliberately left unclosed. A connection is a lazy handle and the channel it names is owned by the pooling layer, which reaps it by refcount and TTL; closing one here would evict a channel the replacement may still share. BREAKING CHANGE: LoadBalancerContextView.workers is now keyed by uuid.UUID rather than WorkerMetadata, mapping each uid to a (metadata, connection) pair. A custom balancer that iterates context.workers.items() must iterate values() instead, and one that tests membership with a metadata record must test with record.uid. LoadBalancerContextLike.update_worker no longer accepts the upsert keyword; call add_worker to admit a worker that may not be pooled yet.
A balancer yielded the (metadata, connection) pair it had read from the pool, and the proxy dispatched through whatever pair it was handed. But a balancer selects from a view it may have read before a discovery refresh replaced a worker's entry: round-robin re-snapshots once per wrap, and a custom balancer may snapshot once per call. The connection it yielded could therefore name the worker's superseded address, which left every balancer that does not check for it dispatching to a dead endpoint — including the three this package documents as examples. Yield the worker's uid instead. A selection names a worker; the proxy resolves that name against the live pool at the moment it dispatches, so a balancer cannot route a task to a superseded address however stale the view it chose from. The staleness stops being something balancer authors must defend against and becomes something they cannot express. The connection half of the yield was a round trip in any case: the balancer took a connection out of the pool and handed it back to the proxy, which owns the pool. It was also the half that went stale. Balancers that need a record or a connection to decide — to match tags, pin a version, weigh a connection — still read them from the context; they simply no longer carry what they read back across the boundary. The success echo narrows with the yield: asend now sends back the uid. Selecting a worker that has left the pool is no longer an error the balancer must avoid. The proxy finds no entry, asks for the next candidate, and reports nothing back, since a worker that has departed has not failed a dispatch. BREAKING CHANGE: LoadBalancerLike.delegate now yields uuid.UUID rather than a (WorkerMetadata, WorkerConnection) pair, and receives a uuid.UUID from asend. A custom balancer yields the uid it selected: "yield metadata, connection" becomes "yield uid". Records and connections remain available through context.workers, which maps each uid to its current (metadata, connection) pair.
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