import { EventEmitter } from "node:events";import { PassThrough } from "node:stream";import { query, type SpawnOptions, type SpawnedProcess } from "@anthropic-ai/claude-agent-sdk";import { afterEach, describe, expect, it } from "vitest"; async function* emptyPrompt(): AsyncGenerator<never, void, void> {} class FakeClaudeCodeProcess implements SpawnedProcess {  readonly stdin = new PassThrough();  readonly stdout = new PassThrough();  killed = false;  exitCode: number | null = null;   private readonly events = new EventEmitter();  private bufferedInput = "";   constructor(    private readonly onMessage: (      message: Record<string, unknown>,      process: FakeClaudeCodeProcess,    ) => void,  ) {    this.stdin.setEncoding("utf8");    this.stdin.on("data", (chunk: string) => {      this.bufferedInput += chunk;      this.drainInput();    });  }   emitJson(message: unknown): void {    this.stdout.write(`${JSON.stringify(message)}\n`);  }   kill(_signal: NodeJS.Signals): boolean {    this.killed = true;    this.exitCode = 0;    this.stdout.end();    this.events.emit("exit", 0, null);    return true;  }   on(    event: "exit" | "error",    listener:      | ((code: number | null, signal: NodeJS.Signals | null) => void)      | ((error: Error) => void),  ): void {    this.events.on(event, listener);  }   once(    event: "exit" | "error",    listener:      | ((code: number | null, signal: NodeJS.Signals | null) => void)      | ((error: Error) => void),  ): void {    this.events.once(event, listener);  }   off(    event: "exit" | "error",    listener:      | ((code: number | null, signal: NodeJS.Signals | null) => void)      | ((error: Error) => void),  ): void {    this.events.off(event, listener);  }   private drainInput(): void {    while (true) {      const newlineIndex = this.bufferedInput.indexOf("\n");      if (newlineIndex === -1) {        return;      }      const line = this.bufferedInput.slice(0, newlineIndex).trim();      this.bufferedInput = this.bufferedInput.slice(newlineIndex + 1);      if (line.length === 0) {        continue;      }      this.onMessage(JSON.parse(line) as Record<string, unknown>, this);    }  }} describe("Claude SDK fast mode probe", () => {  let activeQuery: ReturnType<typeof query> | null = null;   afterEach(() => {    activeQuery?.close();    activeQuery = null;  });   it("passes fast mode through the SDK settings flag", async () => {    let spawnOptions: SpawnOptions | undefined;     activeQuery = query({      prompt: emptyPrompt(),      options: {        persistSession: false,        settings: {          fastMode: true,        },        spawnClaudeCodeProcess: (options): SpawnedProcess => {          spawnOptions = options;          return new FakeClaudeCodeProcess((message, process) => {            if (              message.type !== "control_request" ||              typeof message.request_id !== "string" ||              !message.request ||              typeof message.request !== "object" ||              (message.request as { subtype?: unknown }).subtype !== "initialize"            ) {              return;            }             process.emitJson({              type: "control_response",              response: {                subtype: "success",                request_id: message.request_id,                response: {                  commands: [],                  agents: [],                  output_style: "default",                  available_output_styles: ["default"],                  models: [],                  account: {                    subscriptionType: "max",                  },                  fast_mode_state: "on",                },              },            });          });        },      },    });     const initialization = await activeQuery.initializationResult();    expect(initialization.fast_mode_state).toBe("on");     expect(spawnOptions).toBeDefined();    const settingsFlagIndex = spawnOptions?.args.indexOf("--settings") ?? -1;    expect(settingsFlagIndex).toBeGreaterThan(-1);    expect(JSON.parse(spawnOptions?.args[settingsFlagIndex + 1] ?? "")).toEqual({      fastMode: true,    });  });});