one of the acceptance criteria from the doc is to

Implement all necessary testing (unit, integration, e2e) and metrics.
we don't have e2e tests , is it because feature is not available in atlas ?

We don't have e2e testing yet at a drivers level, I'm expecting this work flow should be convered by a Drivers rather than the doc.

I'll make sure to add a DRIVERS ticket to ensure its documented in the Specs repo and / or unified tests are added.

what about knnVector ? From the doc I understood that index could be created with knnVector field

{
  "mappings": {
    "dynamic": false,
    "fields": {
      "embeddings": {
        "type": "knnVector",

Should we add a fluent index builder that can set type to knnVector ?

The index work was covered in #1960 - this is for creating the query eg:

{
  $search: {
    "index": "<index name>", // optional, defaults to "default"
    "vectorSearch": {
      "exact": true | false,
      "path": "<field-to-search>",
      "queryVector": [<array-of-numbers>],
      "filter": {<filter-specification>},
      "limit": <number-of-results>,
      "numCandidates": <number-of-candidates>,
      "score": {<options>}
    }
  }
}

Which can be done via:

  SearchOperator.vectorSearch(
          fieldPath("embedding"),
          asList(1.0, 2.0),
          10,
          50
  ).filter(SearchOperator.text(fieldPath("title"), "hello"))
          .score(boost(2f))

I added VectorSearchOperator to allow for overrides that vector search can do but aren't general for all SearchOperator instances. VectorSearchOperatorConstructibleBsonElement is the actual implementation for creating the bson.

This follows the existing SearchOperator conventions and builds upon them for vector search.