OpenCode Go session header is not correctly set

Describe the bug

Trying to use OpenCode Go as an AI provider gives the following error:

status_code: 400, model_name: deepseek-v4-flash, body: {'type': 'MissingSessionID', 'message': 'Error from provider (Console Go): Request is missing x-opencode-session and cannot be routed efficiently. Please see https://opencode.ai/docs/go/#where-can-i-use-it'}

The given link explains the situation.

Will you submit a PR?

• Yes

Environment

{
  "marimo": "0.24.2",
  "editable": false,
  "OS": "Windows",
  "OS Version": "11",
  "Processor": "Intel64 Family 6 Model 154 Stepping 3, GenuineIntel",
  "Python Version": "3.14.2",
  "Locale": "English_United Kingdom",
  "Binaries": {
    "Browser": "150.0.7871.187",
    "Node": "v25.9.0",
    "uv": "0.12.2 (x86_64-pc-windows-msvc)"
  },
  "Dependencies": {
    "click": "8.5.0",
    "docutils": "0.23",
    "itsdangerous": "2.2.0",
    "jedi": "0.19.2",
    "markdown": "3.10.3",
    "narwhals": "2.26.0",
    "packaging": "26.3",
    "psutil": "7.2.2",
    "pygments": "2.21.0",
    "pymdown-extensions": "11.0.2",
    "pyyaml": "6.0.3",
    "starlette": "1.6.0",
    "tomlkit": "0.15.1",
    "typing-extensions": "4.16.0",
    "uvicorn": "0.53.0",
    "websockets": "16.1.1"
  },
  "Optional Dependencies": {
    "altair": "6.3.0",
    "loro": "1.13.2",
    "mcp": "2.2.0",
    "openai": "3.14.1"
  },
  "Experimental Flags": {}
}

Code to reproduce

No response