Implement fast userspace multihop mesh routing
Replace the one-intermediate-peer relay with protocol-scoped connectivity graphs and precomputed shortest-path/ECMP forwarding snapshots. Independent transport readers forward opaque transit frames without a plugin or TUN round trip. Carry source, destination, a bounded hop limit and stable flow tags; preserve end-to-end WireGuard links across topology changes. Classify IP flows before encryption and preserve their tags through the WireGuard pending queue. Add offline four-agent path-change coverage, loop and isolation tests, and an opt-in release forwarding microbenchmark. Bump control/data ALPNs while preserving persistent network identities and state. Also include the pending Windows Mainline idle-timeout fix and its regression test, using a reproducible vendored dependency patch. Validation: fmt, workspace Clippy with warnings denied, and 307 release tests passed. Two pre-existing Windows SQLite wipe failures were excluded; public DHT and the manual benchmark remain ignored by default. The forwarding microbenchmark measured 103 ns (64 B) and 202 ns (1280 B) per transit packet, excluding encryption and socket I/O.
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