OpenRouter free-tier models report incorrect costs

[Sanjeev-S]

Bug

OpenRouter free-tier models report GPT-4o default pricing (~$2.50/$10.00 per 1M tokens) instead of $0 in IronClaw UI.

Reproduction

Set .env:

LLM_BACKEND=openai_compatible
LLM_BASE_URL=https://openrouter.ai/api/v1
LLM_API_KEY=sk-or-...
LLM_MODEL=openrouter/free

Send any message. Logs show:

DEBUG LLM call used 7749 input + 180 output tokens ($0.021172)

Root cause

src/llm/costs.rs model_cost() strips the provider prefix via rsplit_once('/'), leaving free. This doesn't match any known model or the is_local_model() heuristic, so it falls back to default_cost() (GPT-4o pricing).

Same issue for any OpenRouter model with the :free suffix (e.g. stepfun/step-3.5-flash:free).

Expected behavior

All models with the :free suffix and the openrouter/free router should report zero cost.