feat(telemetry): Add userId and sessionId metadata to experimental_telemetry

[Raviguntakala]

Summary

Adds userId and sessionId to experimental_telemetry.metadata across all AI SDK calls, enabling session-level trace grouping in observability platforms.

Motivation

Currently, OpenCode emits OTEL traces for cost and token usage tracking, but lacks user/session context. This makes it difficult to:

• Group traces by user sessions
• Track conversation flows end-to-end
• Correlate multiple LLM calls within a single session

Testing

• Tested with Langfuse ✅ - traces correctly group by session and display user attribution
• No impact on existing functionality when OTEL is disabled

[omercnet]

@Raviguntakala how did you test this with langfuse? I'm not seeing the session/user grouping
check out https://github.com/omercnet/opencode-plugin-langfuse let me know if I'm doing something wrong

[Raviguntakala]

@Raviguntakala how did you test this with langfuse? I'm not seeing the session/user grouping check out https://github.com/omercnet/opencode-plugin-langfuse let me know if I'm doing something wrong

Hey @omercnet your plugin looks fine. No issue from Langfuse plugin side.

The reason you’re not seeing user/session grouping is from OpenCode side. After my PR got merged, Dax did a rework on the LLM calls and in that rework the userId and sessionId propagation got removed (not being passed into experimental_telemetry.metadata for LLM calls).

So Langfuse is receiving spans, but without userId/sessionId metadata, it can’t show user level / session level grouping.

I’ll raise another PR with the latest code changes to restore passing userId and sessionId across all LLM calls.

[Raviguntakala]

@Raviguntakala how did you test this with langfuse? I'm not seeing the session/user grouping check out https://github.com/omercnet/opencode-plugin-langfuse let me know if I'm doing something wrong

Opened a follow up PR to fix this: #8195