[RELATIONSHIPS] Update entity overwrites duplicate relationship keys in a single update

[zaeema-n]

Summary

When updating an entity with multiple relationships that share the same relationship key (e.g. two MANDATES edges from one Act to different targets), only one relationship is persisted. The other is dropped or overwritten. This blocks valid graph patterns where one source node should have multiple outgoing edges of the same type in one update request.

Environment

• API: OpenGIN ingestion — PUT /entities/{id}
• Backend: Neo4j handler (HandleGraphEntityUpdate path, inferred from server logs)
• Observed: 2026-06-02

Steps to reproduce

1. Create a source entity (e.g. Universities Act, Document/act).
2. Create two target entities:
   • Target A: University Grants Commission (organisation)
   • Target B: Commission Meeting (event)
3. Send one update to the source entity with two relationships, both using key MANDATES and distinct value.id values:

{
  "id": "<source_id>",
  "relationships": [
    {
      "key": "MANDATES",
      "value": {
        "id": "<rel_id_1>",
        "name": "MANDATES",
        "relatedEntityId": "<target_a_id>",
        "startTime": "2026-06-02T00:00:00Z",
        "endTime": ""
      }
    },
    {
      "key": "MANDATES",
      "value": {
        "id": "<rel_id_2>",
        "name": "MANDATES",
        "relatedEntityId": "<target_b_id>",
        "startTime": "2026-06-02T00:00:00Z",
        "endTime": ""
      }
    }
  ]
}