Problem:

I am trying to use `collection.createSearchIndex()` and `collection.updateSearchIndex()` to programmatically manage a vector search index.

Here's the shape of the index definition:

const index = {
  name: "test_vector_search_index",
  type: "vectorSearch",
  definition: {
    fields: [...],
  },
};

When I call `collection.createSearchIndex(index)` with this definition, it creates the index with no problems.

However, when I call `collection.updateSearchIndex(index.name, index.definition)`, it throws the following error:

MongoServerError: "userCommand.mappings" is required
    at Connection.sendCommand (.../npm_mongodb_6.13.0-6d6f49b5/files/src/cmap/connection.ts:548:17)
    at Connection.command (.../npm_mongodb_6.13.0-6d6f49b5/files/src/cmap/connection.ts:622:22)
    at Server.command (.../npm_mongodb_6.13.0-6d6f49b5/files/src/sdam/server.ts:335:21)
    at UpdateSearchIndexOperation.execute (.../npm_mongodb_6.13.0-6d6f49b5/files/src/operations/search_indexes/update.ts:34:5)
    at tryOperation (.../npm_mongodb_6.13.0-6d6f49b5/files/src/operations/execute_operation.ts:283:14)
    at executeOperation (.../npm_mongodb_6.13.0-6d6f49b5/files/src/operations/execute_operation.ts:115:12)
    at Collection.updateSearchIndex (.../npm_mongodb_6.13.0-6d6f49b5/files/src/collection.ts:1265:12)
    [local frames]
{
  errorLabelSet: Set(0) {},
  errorResponse: {
    ok: 0,
    errmsg: '"userCommand.mappings" is required',
    code: 8,
    codeName: 'UnknownError',
    '$clusterTime': {
      clusterTime: new Timestamp({ t: 1745871047, i: 39 }),
      signature: [Object]
    },
    operationTime: new Timestamp({ t: 1745871047, i: 39 })
  },
  ok: 0,
  code: 8,
  codeName: 'UnknownError',
  '$clusterTime': {
    clusterTime: new Timestamp({ t: 1745871047, i: 39 }),
    signature: {
      hash: Binary.createFromBase64('AAAAAAAAAAAAAAAAAAAAAAAAAAA=', 0),
      keyId: 0
    }
  },
  operationTime: new Timestamp({ t: 1745871047, i: 39 })
} 

However, the documentation for search indexes clearly states that `mappings` is only required for regular search indexes, not vector search indexes.

• https://www.mongodb.com/docs/atlas/atlas-search/searching/#define-your-index
• https://www.mongodb.com/docs/atlas/atlas-vector-search/vector-search-type/#syntax

I believe there is incorrect validation going on, either client side (in the Node.js driver) or server-side. Please correct me if I am wrong and show me the correct way to update a vector index.

Most of the template below is not applicable.

======

Use Case

As a... developer
I want... this bug fixed
So that... I can update search indexes programmatically

User Experience

• What is the desired/expected outcome for the user once this ticket is implemented?
• If bug: What is the number of impacted customers? How severe is the impact? Is anyone blocked or broken?

Dependencies

• upstream and/or downstream requirements and timelines to bear in mind

Risks/Unknowns

• What could go wrong while implementing this change? (e.g., performance, inadvertent behavioral changes in adjacent functionality, existing tech debt, etc)
• Is there an opportunity for better cross-driver alignment or testing in this area?
• Is there an opportunity to improve existing documentation on this subject?

Acceptance Criteria

Implementation Requirements

• functional reqs, potential snafus to avoid, performance targets, etc

Testing Requirements

• unit test, spec test sync, etc

Documentation Requirements

• DOCSP ticket, API docs, etc

Follow Up Requirements

• additional tickets to file, required releases, etc
• if node behavior differs/will differ from other drivers, confirm with dbx devs what standard to aim for and what plan, if any, exists to reconcile the diverging behavior moving forward