Cover the three main abstractions (Router, Chain, Transport), route traversal
lifecycle (Dial → Handshake → Connect), and multiplexing sub-route splitting.
- transport.go: Copy() returned original pointer instead of the allocated copy,
causing data races and incorrect routing for multiplexed chains.
- route.go: Connect and Handshake failures in intermediate nodes leaked the
returned connection. Handshake fix preserves the original Connect result
(guaranteed non-nil) and closes both the Handshake return value and input.
- router.go: defer cancel() inside retry loops accumulated context timers
across iterations. Wrapped each loop body in an IIFE so defer scopes
per-iteration and timers are released immediately.
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