When the tracker proxies /v1/chat/completions to a first-shard node it
already holds the full registry picture. It now resolves the downstream
route inline via _select_route, strips the proxied node, and sends the
result as X-Meshnet-Route header alongside the request body.
The first-shard node reads this header in _get_remaining_route and
returns it directly, skipping the second tracker HTTP call entirely.
Falls back to the tracker query transparently when the header is absent
(direct node-to-node calls or older tracker versions).
Reduces per-inference tracker round-trips from 2 to 1.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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