[Bug] "OpenCode's free tier can only be used from within OpenCode" error when using Custom Agents

Description

Describe the bug
I am encountering an error when attempting to use a custom agent configuration within OpenCode. The request fails, and the console outputs the following error message:

Error from provider (Console): OpenCode's free tier can only be used from within OpenCode

To Reproduce
Configure a custom agent (e.g., modifying the configuration to use a specific model or custom prompt).

Trigger the agent within the OpenCode environment.

Observe the error in the console output.

Expected behavior
The custom agent should execute normally using the available free tier, as it is being invoked from within the OpenCode application.

Actual behavior
The provider rejects the request, stating that the free tier can only be used "within OpenCode," despite the request originating from the OpenCode client.

Additional Context
It appears the provider's validation logic might be incorrectly identifying the custom agent request as an external or unauthorized source.

Attached is a screenshot of the specific error message.

Plugins

No response

OpenCode version

1.18.31

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

No response

Terminal

No response

Start by reproducing the custom-agent request described for OpenCode 1.18.31 and trace the provider request and its free-tier validation. Compare a custom-agent invocation with a normal OpenCode request; done means the custom agent executes without the provider rejecting it as external.