[FR] Support using a similarity threshold in Firestore retriever

[ssbushi]

Is your feature request related to a problem? Please describe. Firestore retriever does not support using a similarity threshold (instead of k) when retrieving documents.

Describe the solution you'd like An optional threshold config that lets developers specify a threshold for the retrieved documents.

Describe alternatives you've considered Existing workaround:

• Manually implement a cutoff mechanism as a post-retrieval step.

Consider extending this support to other retrievers.

Additional context See Discord

[mbleigh]

I don't think Firestore generally supports threshold-based querying (see docs) which makes it difficult to add to the Firestore retriever.

[peterfriese]

/cc @MarkDuckworth for viz

[ssbushi]

@mbleigh Yes, this is not natively supported in Firestore. Which means that this should be handled in the retriever definition after Firestore returns the appropriate documents.

[MarkDuckworth]

This is a feature we are considering implementing natively.

[ssbushi]

This is now natively supported in Firestore https://firebase.google.com/docs/firestore/vector-search#distance-threshold

[ssbushi]

Fixed in https://github.com/firebase/genkit/pull/2246