@effect/ai-openrouter streamText fails when a toolkit is present

[fabstorres]

What version of Effect is running?

effect: 3.20.0, @effect/ai: 0.34.0, @effect/ai-openrouter: 0.9.0

What steps can reproduce the bug?

If the toolkit option is removed from LanguageModel.streamText, the program runs successfully.

The failure only occurs when a toolkit is present.

import { LanguageModel, Prompt, Tool, Toolkit } from "@effect/ai";
import { OpenRouterClient, OpenRouterLanguageModel } from "@effect/ai-openrouter";
import { FetchHttpClient } from "@effect/platform";
import { Config, Effect, Layer, Schema, Stream } from "effect";

const StepFun = OpenRouterLanguageModel.model("stepfun/step-3.5-flash:free");

const SafeUser = Schema.Struct({
  firstName: Schema.String,
  ageRange: Schema.Literal("18-24", "25-34", "35-44", "45+"),
});

const GetUser = Tool.make("GetUser", {
  description: "Get non-sensitive information about the user",
  success: SafeUser,
  failure: Schema.Never,
});

const GetUserTools = Toolkit.make(GetUser);

const GetUserHandlers = GetUserTools.toLayer({
  GetUser: () =>
    Effect.succeed({
      firstName: "John Doe",
      ageRange: "25-34",
    }),
});

const program = LanguageModel.streamText({
  prompt: Prompt.make("Use GetUser tool and tell me about the current user."),
  toolkit: GetUserTools,
}).pipe(Stream.runDrain, Effect.provide(StepFun));

const OpenRouter = OpenRouterClient.layerConfig({
  apiKey: Config.redacted("OPENROUTER_API_KEY"),
}).pipe(Layer.provide(FetchHttpClient.layer));

program.pipe(Effect.provide([OpenRouter, GetUserHandlers]), Effect.runPromise);

What is the expected behavior?

LanguageModel.streamText should work when a Toolkit is provided and allow the model to call tools during streaming without throwing a MalformedOutput error.

What do you see instead?

(FiberFailure) MalformedOutput: { "module": "OpenRouterClient", "method": "streamRequest", "description": undefined, "cause": (parseJson <-> (@effect/ai-openrouter/ChatStreamingResponseChunk (Encoded side) <-> @effect/ai-openrouter/ChatStreamingResponseChunk))

Relevant part of the cause:
["type"] is missing

Actual streamed tool call chunk:
[{"index":0,"function":{"arguments":"{}"}}]

Additional information

No response