LiteLLM proxy responses record $0.00 cost when x-litellm-response-cost header is omitted #52127

Description

When using OpenCode with a LiteLLM proxy, some turns are recorded with $0.00 cost in opencode stats even though the proxy correctly billed the request.

LiteLLM 1.98+ omits the x-litellm-response-cost response header when its value equals x-litellm-response-cost-original (a size optimisation). OpenCode does not read any LiteLLM response headers — cost is estimated purely from a local price table. For models with no price entry, this always yields $0.00. Two manual curl calls to the proxy with identical payloads confirmed the issue: request 1 returned x-litellm-response-cost: 0.000434; request 2 omitted that header but included x-litellm-response-cost-original: 0.000434, yet x-litellm-key-spend incremented on both.

Steps to reproduce

1. Configure OpenCode with a LiteLLM provider (custom proxy or hosted router)
2. Send a prompt using a model that has no local price entry (e.g. litellm/gpt-6-luna)
3. Run opencode stats — cost for that model shows $0.00

Screenshot and/or share link

N/A

OpenCode version

1.18.30

Operating System

Windows 10 Enterprise 25H2 (Build 26200)

Terminal

Windows Terminal