Seller serve returns mock inference — Ollama BaseURL not set from control profile

[ArchieIndian]

The seller node built from the control profile has no Ollama config (node.Ollama is nil). The engine factory falls back to MockBackend, returning "mock-result:mock-response" instead of real Ollama inference.

Root cause: SellerNodeFromControl() extracts skills and pricing but never sets the Ollama field. The control plane does not store the Ollama base URL.

Fix: add --ollama-url flag to seller serve. When provided, sets node.Ollama with BaseURL and models from the control profile, enabling real HTTPBackend.