Support and document custom attached services for Message UCAs / expose supported Event Manager publish pattern

We request IBM to officially support, expose, or document a supported pattern for using custom attached services with Message Undercover Agents used by BPD message events.

Currently, a Message UCA works correctly when using the built-in attached service Default BPD Event with:

correlationKey : String value : String

However, replacing this service with a custom General System Service or Service Flow using the same variable names and types does not trigger the receiving BPD Message Start Event / Event Subprocess. IBM Support confirmed that Default BPD Event has internal Event Manager publishing behavior that a normal custom service does not reproduce.

This creates a limitation because customers cannot safely add custom logic, validation, auditing, transformation, or tracing around UCA message publishing unless they keep Default BPD Event as the final publisher.

Current Behavior

A Message Intermediate Event attached to a UCA triggers the parent BPD event subprocess only when the UCA uses Default BPD Event.

If the UCA uses a custom service with the same contract:

Input: correlationKey String value String Output: correlationKey String value String

the message is not consumed by the running parent process, and correlation does not occur.

Business Impact

Customers need a supported way to customize message event handling for real-world process integrations, including:

• auditing sent and received UCA messages

• logging correlation keys and payloads

• validating payloads before publishing

• transforming message content

• adding security or routing logic

• standardizing reusable event-publishing services across projects

Because the internal behavior of Default BPD Event is not exposed or clearly documented, developers may create custom services that appear contract-compatible but fail at runtime, causing confusion and production risk.

Requested Enhancement

Please provide one or more of the following:

1. Official support for custom attached services that can publish Message UCA events into Event Manager using the same behavior as Default BPD Event.

2. A documented public API or supported system service that custom services can call to publish BPD message events with correlation metadata.

3. A documented service template or toolkit artifact showing the supported pattern:

UCA -> Custom Service -> Default BPD Event

4. Product documentation clearly stating that Default BPD Event has special internal handling and cannot be replaced by a normal service simply by matching variable names.

5. Clear guidance on required service type, input/output contract, correlation handling, durable subscription behavior, and limitations.

Expected Outcome

Developers should be able to create custom UCA attached services without losing Event Manager correlation behavior, or at minimum have clear official documentation explaining the required pattern.

Acceptance Criteria

• IBM documentation explains why Default BPD Event is special.

• IBM documents whether custom attached services are supported for Message UCAs.

• IBM provides a supported way to invoke the same Event Manager publish behavior from custom logic.

• Sample implementation is provided for a custom service that logs or validates data and then correctly publishes the message to a correlated BPD event subprocess.

• Behavior is documented for IBM BPM 8.6 and current BAW releases.

Reference Case

IBM Support case: TS022099377

Support explanation received: Default BPD Event has internal Event Manager handling that is not reproduced by a normal custom service, even with identical correlationKey and value variables.