[Feature]: Represent multi-instance loop characteristics in the process JSON

[DaAnda97]

Summary

As a consumer of the process JSON, I want multi-instance activities to be represented in the surface so that I can tell a looping activity apart from a single-instance one and know whether it runs sequentially or in parallel.

Motivation

Multi-instance is a first-class BPMN execution semantic: it turns a single execution into a loop, and sequential vs. parallel changes token behavior fundamentally. Currently an activity carrying <bpmn:multiInstanceLoopCharacteristics> appears in flowNodes identical to a normal activity — the loop information is dropped. Any consumer reasoning about execution behavior (code generation, analysis, agents) is therefore missing it.

Proposed Solution

Add an additive multiInstance object to the flow node when loop characteristics are present:

{
  "id": "Activity_1",
  "elementType": "SERVICE_TASK",
  "properties": { "…": "…" },
  "multiInstance": {
    "sequential": true,
    "inputCollection": "=items",
    "inputElement": "item",
    "outputCollection": null,
    "outputElement": null,
    "completionCondition": "=done"
  }
}

Derived from:

<bpmn:multiInstanceLoopCharacteristics isSequential="true">
  <bpmn:extensionElements>
    <zeebe:loopCharacteristics inputCollection="=items" inputElement="item" />
  </bpmn:extensionElements>
  <bpmn:completionCondition xsi:type="bpmn:tFormalExpression">=done</bpmn:completionCondition>
</bpmn:multiInstanceLoopCharacteristics>

Acceptance Criteria

• Represented for serviceTask, userTask, callActivity, subProcess
• sequential (from isSequential) distinguishes sequential from parallel
• Absent when the activity has no loop characteristics (backward compatible)

Alternatives Considered

No response