[FEATURE]: Support _meta when calling downstream MCP tools

[Rajmehta123]

When opencode receives a tools/call request that contains _meta, that metadata does not appear to be forwarded when opencode invokes downstream MCP tools.

In a typical setup:

UI → opencode → downstream MCP server

the UI may attach runtime metadata in _meta (for example document IDs, container IDs, workspace context, or tracing information). This metadata is intended to travel with the request but remain hidden from the LLM.

Currently, when opencode makes the downstream tools/call, the _meta field is dropped. As a result, downstream MCP servers lose request-scoped context.

Example incoming request:

{
  "method": "tools/call",
  "params": {
    "name": "docuai_agent_tool",
    "arguments": {
      "user_request": {
        "user_input": "Translate this document to French"
      }
    },
    "_meta": {
      "com.example/documentId": "doc_123",
      "com.example/containerId": "cont_456"
    }
  }
}

Expected downstream request:

{
  "method": "tools/call",
  "params": {
    "name": "translate_document_preserving_structure",
    "arguments": {
      "destinationLanguageThreeLetterCode": "fra"
    },
    "_meta": {
      "com.example/documentId": "doc_123",
      "com.example/containerId": "cont_456"
    }
  }
}

Forwarding _meta would allow downstream MCP tools to access request context (e.g., document IDs or workspace metadata) without exposing those values to the model.

It would be helpful if opencode preserved _meta from incoming requests and forwarded it to downstream tools/call requests when present.

[github-actions]

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What needs to be fixed:

• The description appears to be AI-generated (extensive structured prose, tables, JSON examples, and formatted sections are not acceptable per our guidelines). Please replace it with a concise, human-written description of the problem you're experiencing.

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---

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Forward request-scoped MCP _meta from incoming opencode requests to downstream MCP tool calls #16828: Exact duplicate — same title, same author, same content (already closed)

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

Thank you for updating the issue — the description is clear and well-written.

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