fix(llm): restore OpenAI reasoning streams (#28552)

packages/llm/test/provider/golden.recorded.test.ts

@@ -83,6 +83,7 @@ describeRecordedGoldenScenarios([
     tags: ["flagship"],
     scenarios: [
       { id: "text", temperature: false },
+      { id: "reasoning", temperature: false },
       { id: "tool-call", temperature: false },
       { id: "tool-loop", temperature: false },
     ],

packages/llm/test/provider/openai-chat.test.ts

@@ -260,6 +260,32 @@ describe("OpenAI Chat route", () => {
     }),
   )
 
+  it.effect("parses OpenAI-compatible reasoning content deltas", () =>
+    Effect.gen(function* () {
+      const body = sseEvents(
+        { choices: [{ delta: { reasoning_content: "thinking" } }] },
+        { choices: [{ delta: { content: "Hello" } }] },
+        { choices: [{ delta: {}, finish_reason: "stop" }] },
+      )
+
+      const response = yield* LLMClient.generate(request).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(response.reasoning).toBe("thinking")
+      expect(response.text).toBe("Hello")
+      expect(response.events).toMatchObject([
+        { type: "step-start", index: 0 },
+        { type: "reasoning-start", id: "reasoning-0" },
+        { type: "reasoning-delta", id: "reasoning-0", text: "thinking" },
+        { type: "text-start", id: "text-0" },
+        { type: "text-delta", id: "text-0", text: "Hello" },
+        { type: "reasoning-end", id: "reasoning-0" },
+        { type: "text-end", id: "text-0" },
+        { type: "step-finish", index: 0, reason: "stop" },
+        { type: "finish", reason: "stop" },
+      ])
+    }),
+  )
+
   it.effect("assembles streamed tool call input", () =>
     Effect.gen(function* () {
       const body = sseEvents(

packages/llm/test/provider/openai-responses.test.ts

@@ -118,6 +118,7 @@ describe("OpenAI Responses route", () => {
   it.effect("fails immediately when WebSocket is already closed", () =>
     Effect.gen(function* () {
       const error = yield* WebSocketExecutor.fromWebSocket(
+        // oxlint-disable-next-line typescript-eslint/no-unsafe-type-assertion -- fromWebSocket reads readyState before touching WebSocket methods on this branch.
         { readyState: globalThis.WebSocket.CLOSED } as globalThis.WebSocket,
         { url: "wss://api.openai.test/v1/responses", headers: Headers.empty },
       ).pipe(Effect.flip)
@@ -352,6 +353,33 @@ describe("OpenAI Responses route", () => {
     }),
   )
 
+  it.effect("parses reasoning summary stream fixtures", () =>
+    Effect.gen(function* () {
+      const body = sseEvents(
+        { type: "response.reasoning_summary_text.delta", item_id: "rs_1", delta: "thinking" },
+        { type: "response.output_text.delta", item_id: "msg_1", delta: "Hello" },
+        { type: "response.reasoning_summary_text.done", item_id: "rs_1" },
+        { type: "response.completed", response: { id: "resp_1" } },
+      )
+
+      const response = yield* LLMClient.generate(request).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(response.reasoning).toBe("thinking")
+      expect(response.text).toBe("Hello")
+      expect(response.events).toMatchObject([
+        { type: "step-start", index: 0 },
+        { type: "reasoning-start", id: "rs_1" },
+        { type: "reasoning-delta", id: "rs_1", text: "thinking" },
+        { type: "text-start", id: "msg_1" },
+        { type: "text-delta", id: "msg_1", text: "Hello" },
+        { type: "reasoning-end", id: "rs_1" },
+        { type: "text-end", id: "msg_1" },
+        { type: "step-finish", index: 0, reason: "stop" },
+        { type: "finish", reason: "stop" },
+      ])
+    }),
+  )
+
   it.effect("assembles streamed function call input", () =>
     Effect.gen(function* () {
       const body = sseEvents(

packages/llm/test/recorded-golden.ts

@@ -1,5 +1,5 @@
 import type { HttpRecorder } from "@opencode-ai/http-recorder"
-import { describe, type TestOptions } from "bun:test"
+import { describe } from "bun:test"
 import { Effect } from "effect"
 import type { Model } from "../src"
 import { goldenScenarioTags, runGoldenScenario, type GoldenScenarioID } from "./recorded-scenarios"
@@ -17,7 +17,7 @@ type ScenarioInput =
       readonly tags?: ReadonlyArray<string>
       readonly maxTokens?: number
       readonly temperature?: number | false
-      readonly timeout?: number | TestOptions
+      readonly timeout?: number
     }
 
 type TargetInput = {
@@ -38,6 +38,7 @@ const scenarioInput = (input: ScenarioInput) => (typeof input === "string" ? { i
 const scenarioTitle = (id: GoldenScenarioID) => {
   if (id === "text") return "streams text"
   if (id === "tool-call") return "streams tool call"
+  if (id === "reasoning") return "uses reasoning"
   if (id === "image") return "reads image text"
   return "drives a tool loop"
 }

packages/llm/test/recorded-scenarios.ts

@@ -143,6 +143,25 @@ export const imageRequest = (input: {
         : { maxTokens: input.maxTokens ?? 20, temperature: input.temperature ?? 0 },
   })
 
+export const reasoningRequest = (input: {
+  readonly id: string
+  readonly model: Model
+  readonly maxTokens?: number
+  readonly temperature?: number | false
+}) =>
+  LLM.request({
+    id: input.id,
+    model: input.model,
+    system: "Show concise reasoning when the provider supports visible reasoning summaries.",
+    prompt: "Think briefly, then reply exactly with: Hello!",
+    cache: "none",
+    providerOptions: { openai: { reasoningEffort: "low", reasoningSummary: "auto" } },
+    generation:
+      input.temperature === false
+        ? { maxTokens: input.maxTokens ?? 120 }
+        : { maxTokens: input.maxTokens ?? 120, temperature: input.temperature ?? 0 },
+  })
+
 export const runWeatherToolLoop = (request: LLMRequest) =>
   LLMClient.stream({
     request,
@@ -193,7 +212,7 @@ export const expectGoldenWeatherToolLoop = (events: ReadonlyArray<LLMEvent>) =>
   expect(LLMResponse.text({ events }).trim()).toMatch(/^Paris is sunny\.?$/)
 }
 
-export type GoldenScenarioID = "text" | "tool-call" | "tool-loop" | "image"
+export type GoldenScenarioID = "text" | "tool-call" | "tool-loop" | "image" | "reasoning"
 
 export interface GoldenScenarioContext {
   readonly id: string
@@ -215,6 +234,7 @@ export const goldenScenarioTags = (id: GoldenScenarioID) => {
   if (id === "text") return ["text", "golden"]
   if (id === "tool-call") return ["tool", "tool-call", "golden"]
   if (id === "image") return ["media", "image", "vision", "golden"]
+  if (id === "reasoning") return ["reasoning", "golden"]
   return ["tool", "tool-loop", "golden"]
 }
 
@@ -264,6 +284,21 @@ export const runGoldenScenario = (id: GoldenScenarioID, context: GoldenScenarioC
       return
     }
 
+    if (id === "reasoning") {
+      const response = yield* generate(
+        reasoningRequest({
+          id: context.id,
+          model: context.model,
+          maxTokens: context.maxTokens ?? 120,
+          temperature: context.temperature,
+        }),
+      )
+      expect(response.text.trim()).toMatch(/^Hello!?$/)
+      expect(response.usage?.reasoningTokens ?? 0).toBeGreaterThan(0)
+      expectFinish(response.events, "stop")
+      return
+    }
+
     expectGoldenWeatherToolLoop(
       yield* runWeatherToolLoop(
         goldenWeatherToolLoopRequest({
@@ -293,7 +328,7 @@ const usageSummary = (usage: LLMResponse["usage"] | undefined) => {
 const pushText = (summary: Array<Record<string, unknown>>, type: "text" | "reasoning", value: string) => {
   const last = summary.at(-1)
   if (last?.type === type) {
-    last.value = `${last.value ?? ""}${value}`
+    last.value = `${typeof last.value === "string" ? last.value : ""}${value}`
     return
   }
   summary.push({ type, value })