[Go] OpenAI invalid model ID

[gvozdevs]

Describe the bug
When using OpenAI embedding models, I get an error when executing:

POST "https://api.openai.com/v1/embeddings": 400 Bad Request {
        "message": "invalid model ID",
        "type": "invalid_request_error",
        "param": null,
        "code": null
}

To Reproduce

package main

import (
	"context"
	"log"

	"github.com/firebase/genkit/go/ai"
	"github.com/firebase/genkit/go/genkit"
	"github.com/firebase/genkit/go/plugins/compat_oai/openai"
)

func main() {
	ctx := context.Background()
	oai := &openai.OpenAI{}
	gk := genkit.Init(ctx, genkit.WithPlugins(oai))
	em := oai.Embedder(gk, "openai/text-embedding-3-small")
	if em == nil {
		log.Fatal("failed to create embedder")
	}

	dc := ai.DocumentFromText("hello", nil)
	er := &ai.EmbedRequest{
		Input:   []*ai.Document{dc},
		Options: nil,
	}
	rp, err := em.Embed(ctx, er)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("%+v", rp)
}

Expected behavior
Successful embedding

Runtime (please complete the following information):

• OS: MacOS
• Version 15.6.1

** Go version
go version go1.25.0 darwin/arm64

Additional context
Add any other context about the problem here.

[gvozdevs]

PR with possible problem correction #3558