fix(sdk): reject empty effect responses

packages/sdk/src/effect/client.ts

@@ -33,9 +33,17 @@ export const make = (options?: ClientOptions) =>
         })
         .pipe(
           Effect.flatMap(HttpClientResponse.filterStatusOk),
-          Effect.flatMap((response) => response.json),
-          Effect.map((data) => data as A),
+          Effect.flatMap((response) => response.text),
           Effect.mapError((cause) => new ModelsDevError({ cause })),
+          Effect.flatMap((text) =>
+            Effect.try({
+              try: () => {
+                if (text === "") throw new SyntaxError("Unexpected end of JSON input")
+                return JSON.parse(text) as A
+              },
+              catch: (cause) => new ModelsDevError({ cause }),
+            }),
+          ),
         )
 
     return {

packages/sdk/test/effect.test.ts

@@ -3,11 +3,11 @@ import { Effect, Layer } from "effect"
 import { FetchHttpClient } from "effect/unstable/http"
 import { Models, ModelsDevError } from "../src/effect.js"
 
-function stub(data: unknown, init?: ResponseInit) {
+function stubResponse(body: string | null, init?: ResponseInit) {
   const requests: Request[] = []
   const fetch = (async (input: Parameters<typeof globalThis.fetch>[0], requestInit?: RequestInit) => {
     requests.push(new Request(input instanceof URL ? input.href : (input as string), requestInit))
-    return new Response(JSON.stringify(data), {
+    return new Response(body, {
       headers: { "content-type": "application/json" },
       ...init,
     })
@@ -16,6 +16,10 @@ function stub(data: unknown, init?: ResponseInit) {
   return { requests, layer }
 }
 
+function stub(data: unknown, init?: ResponseInit) {
+  return stubResponse(JSON.stringify(data) ?? null, init)
+}
+
 test("providers() succeeds through an injected transport", async () => {
   const { requests, layer } = stub({ anthropic: { id: "anthropic" } })
   const program = Effect.gen(function* () {
@@ -63,6 +67,17 @@ test("non-2xx fails with ModelsDevError in the error channel", async () => {
   expect(error._tag).toBe("ModelsDevError")
 })
 
+test("empty body fails with ModelsDevError", async () => {
+  const { layer } = stubResponse("")
+  const program = Effect.gen(function* () {
+    const client = yield* Models.make()
+    return yield* client.providers()
+  })
+  const error = await program.pipe(Effect.flip, Effect.provide(layer), Effect.runPromise)
+  expect(error).toBeInstanceOf(ModelsDevError)
+  expect(error._tag).toBe("ModelsDevError")
+})
+
 test("Service and layer provide a shared client", async () => {
   const { requests, layer } = stub({ "openai/gpt-oss-120b": { id: "openai/gpt-oss-120b" } })
   const program = Effect.gen(function* () {