Unknown or variable prices are treated as $0, so they pass every cost cap and look free to Jev

[TheCoder30ec4]

Problem

ModelInfo.from_openrouter turns OpenRouter's variable price ("-1") and missing prices into 0.0. Such a model then:

• passes any Limits(max_cost_usd=...), including a cap of $0
• is described to Jev as $0.00/M, so it looks like the cheapest choice

Live examples today: openrouter/auto, openrouter/fusion, openrouter/pareto-code (variable), plus models priced per request or per output type rather than per token.

Reproduce

from model_router import ModelInfo
m = ModelInfo.from_openrouter({"id": "x/y", "context_length": 100000,
                               "pricing": {"prompt": "-1", "completion": "-1"}})
m.cost(10_000, 1_000)  # 0.0

Suggested fix

• Store unknown prices as None instead of 0.0
• ModelInfo.cost() returns None when a price is unknown
• Router._reject_reason: when max_cost_usd is set, reject models with an unknown cost ("price unknown")
• jev._describe: print price unknown instead of $0.00

Done when

• A variable-price model is rejected under a cost cap and never shown as $0
• Tests in tests/test_models.py and tests/test_router.py