[Transform] Search runtime fields are not handled properly during mapping deduction.

[przemekwitek]

Since not available via FieldCapabilities API, transform search runtime fields are not "visible" to the mapping deduction code.
Therefore, the destination index is missing mappings for the aggregation fields based on search runtime fields.
This affects aggregations that copy the mapping type from source (min, max) but not the aggregations that use a fixed mapping type (avg).

[elasticmachine]

Pinging @elastic/ml-core (:ml/Transform)

[jimczi]

We are working on a solution for this, see #68117. You shouldn't need to reimplement that logic, it's much simpler to just rely on field capabilities to do it for you.

[przemekwitek]

We are working on a solution for this, see #68117.

Thanks @jimczi . Sounds like that's exactly what we need. Is this enhancement targeted at 7.12 or later?

[przemekwitek]

FTR, the fix was implemented using the new FieldCapabilitiesRequest.runtime_fields feature mentioned by @jimczi above.