I'm looking for a way to insert "probes" into update rules such that custom information can be passed back to the InferenceResult object. This would allow for a user to inspect (and visualize) information on the rule/message level, which would be helpful when developing custom rule implementations.

I currently have two use-cases in mind:

1. Message statistics can be written to the probe so that the user can inspect (specific) messages;
2. Custom information during rule computations can be returned, for example to check for convergence when iterating within a rule computation.

In a similar way that Meta and Pipeline objects offer context for inbounds collection and rule computation, a probe might be passed to an update rule. Custom information can then be written to the probe, which is returned to the InferenceResult object (perhaps similar to how posteriors are returned).