Improve guidance for subscription correlation key

[barmac]

Problem you would like to solve

When I create a message, I see a field called "Subscription correlation key" which is far from being self-explanatory. Yes, there's a link to the documentation on the Message group, but the guidance is needed specifically for the correlation key.

Proposed solution

Add a tooltip to the field so that users get proper guidance.

Alternatives considered

Leave it as is.

Additional context

Slack conversation: https://camunda.slack.com/archives/C0693F1NFK5/p1739458208936919

[barmac]

This would have to be implemented in bpmn-js-properties-panel.

[abdul99ahad]

What will be the "guidance" in the tooltip?

The correlationKey of a published message can be used to control the process instance creation.

[nikku]

I'd rephrase to

Use the correlation key to control process instance creation (Learn More)

Important:

• Controls process instance creation / is complicated enough, so we cannot explain in a tooltip, but link to the source.

[abdul99ahad]

Controls process instance creation / is complicated enough, so we cannot explain in a tooltip, but link to the source.

We can link the resource in Learn More

[barmac]

I'd rephrase to

Use the correlation key to control process instance creation (Learn More)

Important:

• Controls process instance creation / is complicated enough, so we cannot explain in a tooltip, but link to the source.

This is coming into the right direction, but in this context the correlation key is used to deliver the message to the right process instance. It does not drive the process instance creation.

[barmac]

The relevant part of the doc is at https://docs.camunda.io/docs/8.7/components/modeler/bpmn/message-events/#messages:~:text=The%20correlationKey%20is%20an%20expression%20that%20usually%20accesses%20a%20variable%20of%20the%20process%20instance%20that%20holds%20the%20correlation%20key%20of%20the%20message.%20The%20expression%20is%20evaluated%20on%20activating%20the%20message%20event%20and%20must%20result%20either%20in%20a%20string%20or%20in%20a%20number.

[barmac]

Proposal:

Use the correlation key to correlate the message with a process instance (e.g. `= orderId`). [Learn more](https://docs.camunda.io/docs/8.7/components/modeler/bpmn/message-events/#messages).

[nikku]

Indeed @barmac, you're right in #4833 (comment).

I confused this once again with the behavior when correlating a message to start a process. You cannot define a correlation key there, but the key passed with the message is being used to control instance creation 🙈:

[barmac]

Yes, the correlation key can be passed with a message for instance creation. This is used by Zeebe to prevent duplicate instances, e.g. two process instances initiated for the same orderId (our way to implement idempotence).