Route lookup was using the client-provided model name ("qwen2.5-0.5b") but
the tracker registers nodes under their full hf_repo ("Qwen/Qwen2.5-0.5B-Instruct").
This caused a 404 on /v1/route and the non-tail node fell back to the
"no downstream route available" error message.
Fix: _get_remaining_route now uses server.backend.model_id (the actual hf_repo)
for the tracker query. Skips self by port matching rather than blind route[0] drop.
Also prints a warning when route lookup fails so the cause is visible.
Distributed generation was also only producing 1 token (single greedy argmax
in decode_tail). Replaced with an autoregressive loop: head node encodes the
growing sequence and forwards to the downstream shard each step, collecting
one token per iteration up to max_tokens or EOS.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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