MDC-style properties, in addition to traceId

[stolsvik]

Ability for an initiation, and during the stages, to add more key-value pairs that will follow the flow. Very much like TraceProperties, but is specifically meant like the logger MDC: In addition to a informative traceId, you could add specific values like "customerId"="12345" for any initiation that relates to that customer. The "MDC labels" would be picked up and set on the actual Logger MDC. That way, you could much more easily hunt for log lines referring to this customerId.

Edit 2023-05-26: With the new io.mats3.util.TraceId tool, you can ensure that "TraceId properties" have a standardized way of being presented. This again make it much simpler to let your logging system parse them out and add them to the log document (using Elastic nomenclature), so that they can be searched for.
However, this still precludes adding more properties as you find them through the flow, as the traceId can per its nature only contain information you have at initiation time.