When _select_route picks two nodes with overlapping registrations (e.g.
A:0-22 and B:20-24), the tracker now injects start_layer per hop so B
executes only layers 23-24, not 20-24.
- model_backend: forward_bytes + _run_layers accept start_layer offset;
clamped to shard_start to prevent out-of-bounds indexing
- torch_server: _handle_binary_forward reads X-Meshnet-Start-Layer header;
_run_downstream_pipeline sends it per hop; route is now list[tuple[str,int]]
- server: proxy injects {endpoint, start_layer} objects in X-Meshnet-Route;
/v1/route response includes start_layer per node in the nodes list
- test: fake backends accept start_layer=None kwarg
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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