请求: 在 Jaeger 中按 session_id 聚合跟踪信息

Source 1: X-Model-Affinity header is the only source Plano reads crates/brightstaff/src/handlers/routing_service.rs:76-79:

let session_id: Option<String> = request_headers
    .get(MODEL_AFFINITY_HEADER) // X-Model-Affinity
    .and_then(|h| h.to_str().ok())
    .map(|s| s.to_string());

Same in crates/brightstaff/src/handlers/LLM/mod.rs:97-100. Claude Code does not send this header — it's a Plano-internal header intended for the second turn of an agentic loop after Plano returns it in a response.