Propagate session ID in LLM and MCP requests

[codefromthecrypt]

Summary

Adds goose-session-id header to HTTP requests and _meta.goose-session-id to MCP operations when a session exists. Enables external observability tools like Envoy AI Gateway to correlate requests by session without requiring OpenTelemetry in Goose.

Implementation:

• Task-local storage for session context propagation
• HTTP header injection in api_client (case-insensitive via reqwest)
• MCP metadata injection preserving existing _meta fields (case-insensitive cleanup)
• Integration and unit tests for both HTTP and MCP propagation

Example use case: Configure Envoy AI Gateway with OTEL_AIGW_SPAN_REQUEST_HEADER_ATTRIBUTES=goose-session-id:session.id to send traces to Arize Phoenix grouped by session.

Type of Change

• [x] Feature
• [ ] Bug fix
• [ ] Refactor / Code quality
• [ ] Performance improvement
• [ ] Documentation
• [ ] Tests
• [ ] Security fix
• [ ] Build / Release
• [ ] Other (specify below)

Testing

added tests including an integrated one

Related Issues

Relates to https://github.com/envoyproxy/ai-gateway/issues/1221 which asked for this in other agent frameworks

[codefromthecrypt]

very flexible on this one, too, header naming.. whether it is configurable.. all that!

[codefromthecrypt]

thanks for the advice! I was AWOL but coming online again now. will touch this up tomorrow UTC+8

[codefromthecrypt]

ok rebased and also tried to shred the lines in a good way. if I made things worse lemme know

[codefromthecrypt]

cool I think the live provider red X is due to it not being on a protected branch. probably safe to review!

[michaelneale]

over to you @jamadeo