Go provider: 400 MissingSessionID - x-opencode-session header not sent

Description

When using OpenCode Go provider, requests fail with a 400 error:

400: {"type":"MissingSessionID","message":"Error from provider (Console Go): Request is missing x-opencode-session and cannot be routed efficiently."}

Expected Behavior

The opencode client should send the x-opencode-session header on all requests to the Go provider, or the Go provider should handle requests without it gracefully.

Actual Behavior

The Go backend rejects the request with a 400 error, making the provider unusable.

Environment

• OS: Windows (win32)
• opencode version: latest
• Provider: OpenCode Go

Notes

This appears to be an issue with the opencode client not sending the session header, or the Go provider's routing logic being too strict. Either the client should ensure the header is always sent, or the provider should degrade gracefully when it is missing.