[Feature]: native MCP trace-context propagation (SEP-414) — stdio support, transport-agnostic #62

Is your feature request related to a problem?

To get a single end-to-end distributed trace across opencode → MCP server, W3C trace context has to be propagated into outbound MCP tools/call requests so the server's spans nest under the opencode tool span. Today this is only achievable for HTTP MCP servers, by intercepting outbound requests and injecting the context into the JSON-RPC _meta + headers. Two gaps:

• stdio MCP servers get no trace context — there is no HTTP request to intercept, so their spans never connect to the parent trace.
• Request-interception is a process-wide workaround that carries transport concerns (URL matching, content-length handling, body re-serialization) that belong in the MCP SDK, not a telemetry layer.

Describe the solution you'd like

Adopt SEP-414 ("OpenTelemetry Trace Context Propagation Conventions for _meta", merged into the MCP spec) once the MCP TypeScript SDK ships it. Injecting traceparent / tracestate into _meta at the client session layer is transport-agnostic — it covers stdio and HTTP uniformly and removes the need for any request-interception workaround. The SEP-414 wire format (bare traceparent / tracestate keys directly under params._meta) is straightforward to emit and read.

Describe alternatives you've considered

• Patching child-process stdin for stdio — rejected: that stream is shared with other spawned subprocesses (shells, LSP servers, formatters); mutating it is fragile and risks corrupting non-MCP I/O.
• Spawn-time TRACEPARENT env var — rejected: stdio MCP servers are long-lived and serve many calls, so a spawn-time value would be static rather than per-call.
• Global fetch interception — works for HTTP transports only, and is a workaround rather than a protocol-level fix.

Telemetry type

• Traces (Other), Configuration

Additional context

This depends on upstream work (all three required before it can be wired up end-to-end):

1. MCP TypeScript SDK implements SEP-414 — tracking: Implement SEP-414: Document OpenTelemetry Trace Context Propagation Conventions modelcontextprotocol/typescript-sdk#2196 (related: OpenTelemetry integration out of the box modelcontextprotocol/typescript-sdk#1264, "OpenTelemetry out of the box").
2. opencode upgrades @modelcontextprotocol/sdk to that version.
3. opencode enables the (opt-in) propagation middleware on its MCP client.

References:

• SEP-414 (merged): https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/seps/414-request-meta.md
• TS SDK #2196: Implement SEP-414: Document OpenTelemetry Trace Context Propagation Conventions modelcontextprotocol/typescript-sdk#2196
• TS SDK #1264: OpenTelemetry integration out of the box modelcontextprotocol/typescript-sdk#1264
• python-sdk reference implementation (merged): Add basic OpenTelemetry tracing for client and server requests modelcontextprotocol/python-sdk#2381

Checklist

• I have searched existing issues and discussions for similar feature requests
• I have checked the changelog to see if this already exists