devin-desktop.ts

/**
 * DevinDesktopExecutor — translates OpenAI chat requests to the direct Devin
 * Desktop Connect-protobuf GetChatMessage stream.
 *
 * The upstream still identifies this client as Windsurf. That compatibility
 * identity is intentionally kept private to this transport.
 */

import { randomUUID } from "node:crypto";
import { gunzipSync } from "node:zlib";

import { PROVIDERS } from "../config/constants.ts";
import { buildErrorBody, sanitizeErrorMessage } from "../utils/error.ts";
import { BaseExecutor, mergeUpstreamExtraHeaders, type ExecuteInput } from "./base.ts";

const DEVIN_DESKTOP_BASE_URL = "https://server.codeium.com";
const DEVIN_DESKTOP_CHAT_PATH = "/exa.api_server_pb.ApiServerService/GetChatMessage";
const DEVIN_DESKTOP_AUTH_PATH = "/exa.auth_pb.AuthService/GetUserJwt";
const DEVIN_DESKTOP_CHAT_URL = `${DEVIN_DESKTOP_BASE_URL}${DEVIN_DESKTOP_CHAT_PATH}`;

const DEVIN_UPSTREAM_IDE_NAME = "windsurf";
const VERIFIED_DEVIN_DESKTOP_VERSION = "3.6.27";
// The installed Desktop bundle exposes codeiumVersion 1.48.2. The exact runtime
// getter has not been independently proven, so keep this distinct from the app
// version and allow a validated override rather than claiming they are equal.
const DEFAULT_DEVIN_EXTENSION_VERSION = "1.48.2";
const DEVIN_VERSION_PATTERN = /^\d+\.\d+\.\d+$/;
const DEVIN_LOCALE = "en-US";
const CONNECT_COMPRESSED_FLAG = 0x01;
const CONNECT_END_STREAM_FLAG = 0x02;
const MAX_CONNECT_FRAME_BYTES = 16 * 1024 * 1024;
const MAX_AUTH_RESPONSE_BYTES = 1024 * 1024;

export function resolveDevinDesktopVersion(): string {
  const override = process.env.DEVIN_DESKTOP_VERSION?.trim() ?? "";
  return DEVIN_VERSION_PATTERN.test(override) ? override : VERIFIED_DEVIN_DESKTOP_VERSION;
}

export function resolveDevinDesktopExtensionVersion(): string {
  const override = process.env.DEVIN_DESKTOP_EXTENSION_VERSION?.trim() ?? "";
  return DEVIN_VERSION_PATTERN.test(override) ? override : DEFAULT_DEVIN_EXTENSION_VERSION;
}

const TEXT_ENCODER = new TextEncoder();
const TEXT_DECODER = new TextDecoder();

function encodeVarint(value: number): Uint8Array {
  if (!Number.isSafeInteger(value) || value < 0) throw new Error("invalid protobuf varint");
  const bytes: number[] = [];
  let remaining = value;
  while (remaining >= 0x80) {
    bytes.push((remaining % 0x80) | 0x80);
    remaining = Math.floor(remaining / 0x80);
  }
  bytes.push(remaining);
  return Uint8Array.from(bytes);
}

function concatBytes(arrays: Uint8Array[]): Uint8Array<ArrayBuffer> {
  const total = arrays.reduce((length, bytes) => length + bytes.length, 0);
  const result = new Uint8Array(total);
  let offset = 0;
  for (const bytes of arrays) {
    result.set(bytes, offset);
    offset += bytes.length;
  }
  return result;
}

function bodyArrayBuffer(bytes: Uint8Array): ArrayBuffer {
  const copy = new Uint8Array(bytes.length);
  copy.set(bytes);
  return copy.buffer;
}

function encodeField(fieldNumber: number, payload: Uint8Array): Uint8Array {
  return concatBytes([encodeVarint((fieldNumber << 3) | 2), encodeVarint(payload.length), payload]);
}

function encodeString(fieldNumber: number, value: string): Uint8Array {
  return value ? encodeField(fieldNumber, TEXT_ENCODER.encode(value)) : new Uint8Array(0);
}

function encodeVarintField(fieldNumber: number, value: number): Uint8Array {
  return value === 0
    ? new Uint8Array(0)
    : concatBytes([encodeVarint(fieldNumber << 3), encodeVarint(value)]);
}

export type DevinDesktopToolCallInput = {
  id: string;
  name: string;
  argumentsJson: string;
};

export type DevinDesktopPromptInput = {
  messageId: string;
  source: 1 | 2 | 4;
  prompt: string;
  toolCalls?: DevinDesktopToolCallInput[];
  toolCallId?: string;
};

export type DevinDesktopToolInput = {
  name: string;
  description: string;
  jsonSchemaString: string;
  strict: boolean;
};

export type DevinDesktopToolChoice =
  | { optionName: "auto" | "none" | "required" }
  | {
      toolName: string;
    };

export type DevinDesktopMetadataInput = {
  apiKey: string;
  sessionId: string;
  userJwt?: string;
  ideVersion?: string;
  extensionVersion?: string;
};

export type DevinDesktopRequestInput = DevinDesktopMetadataInput & {
  model: string;
  systemPrompt: string;
  prompts: DevinDesktopPromptInput[];
  cascadeId: string;
  tools?: DevinDesktopToolInput[];
  disableParallelToolCalls?: boolean;
  toolChoice?: DevinDesktopToolChoice;
};

function encodeMetadata(input: DevinDesktopMetadataInput): Uint8Array {
  return concatBytes([
    encodeString(1, DEVIN_UPSTREAM_IDE_NAME),
    encodeString(2, input.extensionVersion ?? resolveDevinDesktopExtensionVersion()),
    encodeString(3, input.apiKey),
    encodeString(4, DEVIN_LOCALE),
    encodeString(7, input.ideVersion ?? resolveDevinDesktopVersion()),
    encodeString(10, input.sessionId),
    encodeString(12, DEVIN_UPSTREAM_IDE_NAME),
    encodeString(21, input.userJwt ?? ""),
  ]);
}

/** Encode the unary GetUserJwtRequest (field 1 = Metadata), without an envelope. */
export function encodeDevinDesktopAuthRequest(input: DevinDesktopMetadataInput): Uint8Array {
  return encodeField(1, encodeMetadata(input));
}

function encodeChatToolCall(toolCall: DevinDesktopToolCallInput): Uint8Array {
  return concatBytes([
    encodeString(1, toolCall.id),
    encodeString(2, toolCall.name),
    encodeString(3, toolCall.argumentsJson),
  ]);
}

function encodeChatMessagePrompt(prompt: DevinDesktopPromptInput): Uint8Array {
  const fields: Uint8Array[] = [
    encodeString(1, prompt.messageId),
    encodeVarintField(2, prompt.source),
    encodeString(3, prompt.prompt),
  ];
  for (const toolCall of prompt.toolCalls ?? []) {
    fields.push(encodeField(6, encodeChatToolCall(toolCall)));
  }
  fields.push(encodeString(7, prompt.toolCallId ?? ""));
  return concatBytes(fields);
}

function encodeChatToolDefinition(tool: DevinDesktopToolInput): Uint8Array {
  return concatBytes([
    encodeString(1, tool.name),
    encodeString(2, tool.description),
    encodeString(3, tool.jsonSchemaString),
    encodeVarintField(12, tool.strict ? 1 : 0),
  ]);
}

function encodeChatToolChoice(choice: DevinDesktopToolChoice): Uint8Array {
  return "optionName" in choice
    ? encodeString(1, choice.optionName)
    : encodeString(2, choice.toolName);
}

/** Encode the verified exa.api_server_pb.GetChatMessageRequest wire schema. */
export function encodeDevinDesktopRequest(input: DevinDesktopRequestInput): Uint8Array {
  const fields: Uint8Array[] = [
    encodeField(1, encodeMetadata(input)),
    encodeString(2, input.systemPrompt),
  ];
  for (const prompt of input.prompts) fields.push(encodeField(3, encodeChatMessagePrompt(prompt)));
  fields.push(encodeVarintField(7, 5)); // CHAT_MESSAGE_REQUEST_TYPE_CASCADE
  for (const tool of input.tools ?? []) {
    fields.push(encodeField(10, encodeChatToolDefinition(tool)));
  }
  if (input.disableParallelToolCalls) fields.push(encodeVarintField(11, 1));
  if (input.toolChoice) fields.push(encodeField(12, encodeChatToolChoice(input.toolChoice)));
  fields.push(
    encodeString(14, input.model),
    encodeString(16, input.cascadeId),
    encodeString(21, input.model)
  );
  return concatBytes(fields);
}

/** Connect streaming envelope: flags byte plus a big-endian uint32 length. */
export function encodeDevinConnectEnvelope(payload: Uint8Array, flags = 0): Uint8Array {
  const frame = new Uint8Array(5 + payload.length);
  frame[0] = flags;
  new DataView(frame.buffer).setUint32(1, payload.length, false);
  frame.set(payload, 5);
  return frame;
}

type OpenAIMessage = {
  role?: string;
  content?: unknown;
  tool_call_id?: string;
  tool_calls?: Array<{
    id?: unknown;
    type?: unknown;
    function?: { name?: unknown; arguments?: unknown };
  }>;
};

function messageText(content: unknown): string {
  if (typeof content === "string") return content;
  if (!Array.isArray(content)) return "";
  let text = "";
  for (const part of content) {
    if (part && typeof part === "object" && (part as Record<string, unknown>).type === "text") {
      text += String((part as Record<string, unknown>).text ?? "");
    }
  }
  return text;
}

function convertHistoryToolCalls(
  toolCalls: OpenAIMessage["tool_calls"]
): DevinDesktopToolCallInput[] {
  if (!Array.isArray(toolCalls)) return [];
  const result: DevinDesktopToolCallInput[] = [];
  for (const toolCall of toolCalls) {
    if (
      toolCall?.type !== "function" ||
      typeof toolCall.id !== "string" ||
      typeof toolCall.function?.name !== "string" ||
      typeof toolCall.function.arguments !== "string"
    ) {
      continue;
    }
    result.push({
      id: toolCall.id,
      name: toolCall.function.name,
      argumentsJson: toolCall.function.arguments,
    });
  }
  return result;
}

function convertMessages(messages: OpenAIMessage[]): {
  systemPrompt: string;
  prompts: DevinDesktopPromptInput[];
} {
  const systemParts: string[] = [];
  const prompts: DevinDesktopPromptInput[] = [];
  for (const message of messages) {
    const role = String(message.role || "user");
    const prompt = messageText(message.content);
    if (role === "system" || role === "developer") {
      if (prompt) systemParts.push(prompt);
      continue;
    }
    const source: 1 | 2 | 4 = role === "assistant" ? 2 : role === "tool" ? 4 : 1;
    prompts.push({
      messageId: source === 2 ? `bot-${randomUUID()}` : randomUUID(),
      source,
      prompt,
      ...(source === 2 ? { toolCalls: convertHistoryToolCalls(message.tool_calls) } : {}),
      ...(source === 4 && message.tool_call_id ? { toolCallId: message.tool_call_id } : {}),
    });
  }
  return { systemPrompt: systemParts.join("\n\n"), prompts };
}

type OpenAIFunctionTool = {
  type?: string;
  function?: {
    name?: unknown;
    description?: unknown;
    parameters?: unknown;
    strict?: unknown;
  };
};

function convertTools(tools: unknown): DevinDesktopToolInput[] {
  if (!Array.isArray(tools)) return [];
  const result: DevinDesktopToolInput[] = [];
  for (const tool of tools as OpenAIFunctionTool[]) {
    if (tool?.type !== "function" || typeof tool.function?.name !== "string") continue;
    result.push({
      name: tool.function.name,
      description: typeof tool.function.description === "string" ? tool.function.description : "",
      jsonSchemaString: JSON.stringify(tool.function.parameters ?? {}),
      strict: tool.function.strict === true,
    });
  }
  return result;
}

function convertToolChoice(choice: unknown): DevinDesktopToolChoice | undefined {
  if (choice === "auto" || choice === "none" || choice === "required") {
    return { optionName: choice };
  }
  if (!choice || typeof choice !== "object") return undefined;
  const record = choice as Record<string, unknown>;
  if (record.type !== "function" || !record.function || typeof record.function !== "object") {
    return undefined;
  }
  const name = (record.function as Record<string, unknown>).name;
  return typeof name === "string" && name ? { toolName: name } : undefined;
}

type ProtoField =
  | { fieldNumber: number; wireType: 0; value: number }
  | { fieldNumber: number; wireType: 1 | 2 | 5; value: Uint8Array };

function readVarint(bytes: Uint8Array, start: number): [number, number] {
  let value = 0;
  let multiplier = 1;
  let offset = start;
  for (let count = 0; count < 10 && offset < bytes.length; count++) {
    const byte = bytes[offset++];
    value += (byte & 0x7f) * multiplier;
    if (!Number.isSafeInteger(value)) throw new Error("protobuf varint exceeds safe range");
    if ((byte & 0x80) === 0) return [value, offset];
    multiplier *= 0x80;
  }
  throw new Error("truncated protobuf varint");
}

function decodeFields(bytes: Uint8Array): ProtoField[] {
  const fields: ProtoField[] = [];
  let offset = 0;
  while (offset < bytes.length) {
    let tag: number;
    [tag, offset] = readVarint(bytes, offset);
    const fieldNumber = Math.floor(tag / 8);
    const wireType = tag & 0x07;
    if (fieldNumber === 0) throw new Error("invalid protobuf field number");
    if (wireType === 0) {
      let value: number;
      [value, offset] = readVarint(bytes, offset);
      fields.push({ fieldNumber, wireType: 0, value });
      continue;
    }
    if (wireType === 1) {
      if (offset + 8 > bytes.length) throw new Error("truncated protobuf fixed64");
      fields.push({ fieldNumber, wireType: 1, value: bytes.slice(offset, offset + 8) });
      offset += 8;
      continue;
    }
    if (wireType === 2) {
      let length: number;
      [length, offset] = readVarint(bytes, offset);
      if (length > bytes.length - offset) throw new Error("truncated protobuf field");
      fields.push({ fieldNumber, wireType: 2, value: bytes.slice(offset, offset + length) });
      offset += length;
      continue;
    }
    if (wireType === 5) {
      if (offset + 4 > bytes.length) throw new Error("truncated protobuf fixed32");
      fields.push({ fieldNumber, wireType: 5, value: bytes.slice(offset, offset + 4) });
      offset += 4;
      continue;
    }
    throw new Error(`unsupported protobuf wire type ${wireType}`);
  }
  return fields;
}

type DevinAuthResponse = { userJwt: string; customApiServerUrl: string };

function decodeDevinAuthResponse(bytes: Uint8Array): DevinAuthResponse {
  const result: DevinAuthResponse = { userJwt: "", customApiServerUrl: "" };
  for (const field of decodeFields(bytes)) {
    if (field.wireType !== 2) continue;
    if (field.fieldNumber === 1) result.userJwt = TEXT_DECODER.decode(field.value);
    else if (field.fieldNumber === 2) {
      // Deliberately decoded but not followed: an unchecked credential-derived
      // URL would create an SSRF path. Enterprise custom endpoints remain a
      // documented limitation until they have a strict validation policy.
      result.customApiServerUrl = TEXT_DECODER.decode(field.value);
    }
  }
  return result;
}

async function readBoundedResponse(response: Response, limit: number): Promise<Uint8Array> {
  const reader = response.body?.getReader();
  if (!reader) return new Uint8Array(0);
  const chunks: Uint8Array[] = [];
  let total = 0;
  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      if (!value?.length) continue;
      total += value.length;
      if (total > limit) {
        await reader.cancel("response exceeds safety limit");
        throw new Error("Devin Desktop auth response exceeds the safety limit");
      }
      chunks.push(value);
    }
  } finally {
    reader.releaseLock();
  }
  return concatBytes(chunks);
}

type DevinUsage = {
  inputTokens: number;
  outputTokens: number;
  cacheWriteTokens: number;
  cacheReadTokens: number;
};

type DevinToolCallDelta = { id: string; name: string; arguments: string };

type DecodedResponse = {
  text: string;
  thinking: string;
  stopReason: number;
  usage: DevinUsage | null;
  toolCalls: DevinToolCallDelta[];
};

function decodeUsage(bytes: Uint8Array): DevinUsage {
  const usage: DevinUsage = {
    inputTokens: 0,
    outputTokens: 0,
    cacheWriteTokens: 0,
    cacheReadTokens: 0,
  };
  for (const field of decodeFields(bytes)) {
    if (field.wireType !== 0) continue;
    if (field.fieldNumber === 2) usage.inputTokens = field.value;
    else if (field.fieldNumber === 3) usage.outputTokens = field.value;
    else if (field.fieldNumber === 4) usage.cacheWriteTokens = field.value;
    else if (field.fieldNumber === 5) usage.cacheReadTokens = field.value;
  }
  return usage;
}

function decodeToolCall(bytes: Uint8Array): DevinToolCallDelta {
  const result: DevinToolCallDelta = { id: "", name: "", arguments: "" };
  for (const field of decodeFields(bytes)) {
    if (field.wireType !== 2) continue;
    if (field.fieldNumber === 1) result.id = TEXT_DECODER.decode(field.value);
    else if (field.fieldNumber === 2) result.name = TEXT_DECODER.decode(field.value);
    else if (field.fieldNumber === 3) result.arguments = TEXT_DECODER.decode(field.value);
  }
  return result;
}

function decodeGetChatMessageResponse(bytes: Uint8Array): DecodedResponse {
  const result: DecodedResponse = {
    text: "",
    thinking: "",
    stopReason: 0,
    usage: null,
    toolCalls: [],
  };
  for (const field of decodeFields(bytes)) {
    if (field.wireType === 2 && field.fieldNumber === 3) {
      result.text += TEXT_DECODER.decode(field.value);
    } else if (field.wireType === 0 && field.fieldNumber === 5) {
      result.stopReason = field.value;
    } else if (field.wireType === 2 && field.fieldNumber === 6) {
      const toolCall = decodeToolCall(field.value);
      if (toolCall.id) result.toolCalls.push(toolCall);
    } else if (field.wireType === 2 && field.fieldNumber === 7) {
      result.usage = decodeUsage(field.value);
    } else if (field.wireType === 2 && field.fieldNumber === 9) {
      result.thinking += TEXT_DECODER.decode(field.value);
    }
  }
  return result;
}

type ConnectTrailerError = { code: string; message: string };

function parseConnectTrailerError(payload: Uint8Array): ConnectTrailerError | null {
  let parsed: unknown;
  try {
    parsed = JSON.parse(TEXT_DECODER.decode(payload).trim() || "{}");
  } catch {
    return { code: "invalid_trailer", message: "Invalid Devin Desktop Connect trailer" };
  }
  if (!parsed || typeof parsed !== "object" || !("error" in parsed)) return null;
  const error = (parsed as { error?: unknown }).error;
  if (!error || typeof error !== "object") {
    return { code: "upstream_error", message: "Devin Desktop Connect stream failed" };
  }
  const record = error as Record<string, unknown>;
  const code = typeof record.code === "string" ? record.code : "upstream_error";
  const message = typeof record.message === "string" ? record.message : "Connect stream failed";
  return { code, message };
}

function finishReason(stopReason: number, hasToolCalls: boolean): string {
  if (hasToolCalls || stopReason === 10) return "tool_calls";
  if (stopReason === 3) return "length";
  if (stopReason === 11) return "content_filter";
  return "stop";
}

function serviceBaseUrl(baseUrl: string): string {
  const normalized = baseUrl.replace(/\/+$/, "");
  for (const path of [DEVIN_DESKTOP_CHAT_PATH, DEVIN_DESKTOP_AUTH_PATH]) {
    if (normalized.endsWith(path)) return normalized.slice(0, -path.length);
  }
  return normalized;
}

function connectChatUrl(baseUrl: string): string {
  return `${serviceBaseUrl(baseUrl)}${DEVIN_DESKTOP_CHAT_PATH}`;
}

function authUrl(baseUrl: string): string {
  return `${serviceBaseUrl(baseUrl)}${DEVIN_DESKTOP_AUTH_PATH}`;
}

function jsonErrorResponse(status: number, message: string): Response {
  return new Response(JSON.stringify(buildErrorBody(status, message)), {
    status,
    headers: { "Content-Type": "application/json" },
  });
}

export class DevinDesktopExecutor extends BaseExecutor {
  constructor() {
    super(
      "devin-desktop",
      PROVIDERS["devin-desktop"] || { id: "devin-desktop", baseUrl: DEVIN_DESKTOP_CHAT_URL }
    );
  }

  buildUrl(): string {
    return DEVIN_DESKTOP_CHAT_URL;
  }

  buildHeaders(_credentials: { accessToken?: string; apiKey?: string }): Record<string, string> {
    // The raw imported key authenticates the GetUserJwt preflight through
    // Metadata.api_key; chat then carries both that key and the returned JWT in
    // Metadata. The proven flow does not construct a Basic Authorization header.
    return {
      "Content-Type": "application/connect+proto",
      Accept: "application/connect+proto",
      "Connect-Protocol-Version": "1",
      "Connect-Accept-Encoding": "gzip",
      "User-Agent": `windsurf/${resolveDevinDesktopVersion()}`,
    };
  }

  transformRequest(): unknown {
    return null;
  }

  async execute({
    model,
    body,
    credentials,
    signal,
    log,
    upstreamExtraHeaders,
  }: ExecuteInput): Promise<{
    response: Response;
    url: string;
    headers: Record<string, string>;
    transformedBody: unknown;
  }> {
    const apiKey = credentials.accessToken || credentials.apiKey || "";
    const baseUrl = this.resolveBaseUrl(credentials, DEVIN_DESKTOP_BASE_URL);
    const url = connectChatUrl(baseUrl);
    const authEndpoint = authUrl(baseUrl);
    const headers = this.buildHeaders(credentials);
    mergeUpstreamExtraHeaders(headers, upstreamExtraHeaders);
    if (!apiKey) {
      return {
        response: jsonErrorResponse(401, "Devin Desktop API key is required"),
        url,
        headers,
        transformedBody: null,
      };
    }

    const requestBody = (body ?? {}) as Record<string, unknown>;
    const messages = Array.isArray(requestBody.messages)
      ? (requestBody.messages as OpenAIMessage[])
      : [];
    const converted = convertMessages(messages);
    if (converted.prompts.length === 0) {
      converted.prompts.push({ messageId: randomUUID(), source: 1, prompt: "" });
    }
    const sessionId = randomUUID();
    const cascadeId =
      typeof requestBody.conversation_id === "string" && requestBody.conversation_id
        ? requestBody.conversation_id
        : randomUUID();

    const authRequest = encodeDevinDesktopAuthRequest({ apiKey, sessionId });
    const authHeaders: Record<string, string> = {
      "Content-Type": "application/proto",
      Accept: "*/*",
      "Connect-Protocol-Version": "1",
    };
    mergeUpstreamExtraHeaders(authHeaders, upstreamExtraHeaders);

    let authResponse: Response;
    try {
      authResponse = await fetch(authEndpoint, {
        method: "POST",
        headers: authHeaders,
        body: bodyArrayBuffer(authRequest),
        signal: signal ?? undefined,
      });
    } catch (error) {
      const aborted = signal?.aborted === true;
      const safe = sanitizeErrorMessage(error instanceof Error ? error.message : String(error));
      log?.warn?.("DEVIN", `Devin Desktop authentication failed: ${safe}`);
      return {
        response: jsonErrorResponse(
          aborted ? 499 : 502,
          aborted ? "Devin Desktop request aborted" : "Devin Desktop authentication failed"
        ),
        url: authEndpoint,
        headers: authHeaders,
        transformedBody: null,
      };
    }
    if (!authResponse.ok) {
      void authResponse.body?.cancel().catch(() => {});
      return {
        response: jsonErrorResponse(
          authResponse.status,
          `Devin Desktop authentication returned HTTP ${authResponse.status}`
        ),
        url: authEndpoint,
        headers: authHeaders,
        transformedBody: null,
      };
    }

    let userJwt: string;
    try {
      const authPayload = await readBoundedResponse(authResponse, MAX_AUTH_RESPONSE_BYTES);
      const authData = decodeDevinAuthResponse(authPayload);
      // Do not follow credential-derived custom_api_server_url values without a
      // dedicated allowlist/SSRF policy; the operator-configured base URL remains authoritative.
      userJwt = authData.userJwt;
      if (!userJwt) throw new Error("Devin Desktop authentication returned an empty user JWT");
    } catch (error) {
      const safe = sanitizeErrorMessage(error instanceof Error ? error.message : String(error));
      log?.warn?.("DEVIN", `Devin Desktop authentication response was invalid: ${safe}`);
      return {
        response: jsonErrorResponse(502, `Devin Desktop authentication failed: ${safe}`),
        url: authEndpoint,
        headers: authHeaders,
        transformedBody: null,
      };
    }

    const protobuf = encodeDevinDesktopRequest({
      apiKey,
      userJwt,
      model,
      systemPrompt: converted.systemPrompt,
      prompts: converted.prompts,
      sessionId,
      cascadeId,
      tools: convertTools(requestBody.tools),
      disableParallelToolCalls: requestBody.parallel_tool_calls === false,
      toolChoice: convertToolChoice(requestBody.tool_choice),
    });
    const framed = encodeDevinConnectEnvelope(protobuf);
    log?.info?.("DEVIN", `Devin Desktop → ${model} (${converted.prompts.length} messages)`);

    let upstream: Response;
    try {
      upstream = await fetch(url, {
        method: "POST",
        headers,
        body: bodyArrayBuffer(framed),
        signal: signal ?? undefined,
      });
    } catch (error) {
      const aborted = signal?.aborted === true;
      const safe = sanitizeErrorMessage(error instanceof Error ? error.message : String(error));
      log?.warn?.("DEVIN", `Devin Desktop Connect request failed: ${safe}`);
      return {
        response: jsonErrorResponse(
          aborted ? 499 : 502,
          aborted ? "Devin Desktop request aborted" : "Devin Desktop upstream connection failed"
        ),
        url,
        headers,
        transformedBody: protobuf,
      };
    }

    if (!upstream.ok) {
      void upstream.body?.cancel().catch(() => {});
      return {
        response: jsonErrorResponse(
          upstream.status,
          `Devin Desktop upstream returned HTTP ${upstream.status}`
        ),
        url,
        headers,
        transformedBody: protobuf,
      };
    }

    return {
      response: this.transformToSSE(upstream, model),
      url,
      headers,
      transformedBody: protobuf,
    };
  }

  private transformToSSE(upstream: Response, model: string): Response {
    const responseId = `chatcmpl-devin-desktop-${Date.now()}`;
    const created = Math.floor(Date.now() / 1000);
    let activeReader: ReadableStreamDefaultReader<Uint8Array> | null = null;

    const stream = new ReadableStream<Uint8Array>({
      async start(controller) {
        const emit = (payload: unknown) => {
          controller.enqueue(TEXT_ENCODER.encode(`data: ${JSON.stringify(payload)}\n\n`));
        };
        const emitChunk = (delta: Record<string, unknown>, reason: string | null = null) => {
          emit({
            id: responseId,
            object: "chat.completion.chunk",
            created,
            model,
            choices: [{ index: 0, delta, finish_reason: reason }],
          });
        };
        const emitError = (message: string) => {
          emit(
            buildErrorBody(502, message, undefined, {
              type: "devin_desktop_error",
              code: "upstream_error",
            })
          );
          controller.enqueue(TEXT_ENCODER.encode("data: [DONE]\n\n"));
        };

        let pending = new Uint8Array(0);
        let roleEmitted = false;
        let stopReason = 0;
        const toolCallIndexes = new Map<string, number>();
        let usage: DevinUsage | null = null;
        let trailerError: ConnectTrailerError | null = null;
        let sawEndStream = false;

        try {
          activeReader = upstream.body?.getReader() ?? null;
          if (!activeReader) throw new Error("Devin Desktop response body is empty");

          const handleFrame = (flags: number, payload: Uint8Array): boolean => {
            if ((flags & ~(CONNECT_COMPRESSED_FLAG | CONNECT_END_STREAM_FLAG)) !== 0) {
              throw new Error("Invalid Devin Desktop Connect frame flags");
            }
            const decodedPayload =
              flags & CONNECT_COMPRESSED_FLAG
                ? gunzipSync(payload, { maxOutputLength: MAX_CONNECT_FRAME_BYTES })
                : payload;
            if (flags & CONNECT_END_STREAM_FLAG) {
              if (sawEndStream) throw new Error("Duplicate Devin Desktop Connect end-stream frame");
              sawEndStream = true;
              trailerError = parseConnectTrailerError(decodedPayload);
              return true;
            }
            const response = decodeGetChatMessageResponse(decodedPayload);
            stopReason = response.stopReason || stopReason;
            usage = response.usage ?? usage;
            if ((response.thinking || response.text || response.toolCalls.length) && !roleEmitted) {
              emitChunk({ role: "assistant", content: "" });
              roleEmitted = true;
            }
            if (response.thinking) emitChunk({ reasoning_content: response.thinking });
            if (response.text) emitChunk({ content: response.text });
            for (const toolCall of response.toolCalls) {
              const existingIndex = toolCallIndexes.get(toolCall.id);
              const index = existingIndex ?? toolCallIndexes.size;
              const firstDelta = existingIndex === undefined;
              if (firstDelta) toolCallIndexes.set(toolCall.id, index);
              const functionDelta: Record<string, string> = {};
              if (toolCall.name) functionDelta.name = toolCall.name;
              if (toolCall.arguments) functionDelta.arguments = toolCall.arguments;
              emitChunk({
                tool_calls: [
                  {
                    index,
                    ...(firstDelta ? { id: toolCall.id, type: "function" } : {}),
                    function: functionDelta,
                  },
                ],
              });
            }
            return false;
          };

          const drain = (): boolean => {
            let offset = 0;
            while (pending.length - offset >= 5) {
              const length = new DataView(
                pending.buffer,
                pending.byteOffset + offset + 1,
                4
              ).getUint32(0, false);
              if (length > MAX_CONNECT_FRAME_BYTES) {
                throw new Error("Devin Desktop Connect frame exceeds the safety limit");
              }
              if (pending.length - offset < 5 + length) break;
              const flags = pending[offset];
              const terminal = handleFrame(flags, pending.slice(offset + 5, offset + 5 + length));
              offset += 5 + length;
              if (terminal) {
                if (pending.length !== offset) {
                  throw new Error("Data follows the Devin Desktop Connect end-stream frame");
                }
                pending = new Uint8Array(0);
                return true;
              }
            }
            if (offset > 0) pending = pending.slice(offset);
            return false;
          };

          while (true) {
            const { done, value } = await activeReader.read();
            if (value?.length) {
              pending = pending.length ? concatBytes([pending, value]) : Uint8Array.from(value);
              if (drain()) {
                await activeReader.cancel("Devin Desktop Connect end-stream received");
                break;
              }
            }
            if (done) break;
          }
          if (!sawEndStream) drain();
          if (pending.length !== 0) throw new Error("Truncated Devin Desktop Connect frame");
          if (!sawEndStream) throw new Error("Devin Desktop Connect stream ended without trailers");
          if (trailerError) {
            const detail = sanitizeErrorMessage(`${trailerError.code}: ${trailerError.message}`);
            emitError(`Devin Desktop stream error: ${detail}`);
            return;
          }

          const finalPayload: Record<string, unknown> = {
            id: responseId,
            object: "chat.completion.chunk",
            created,
            model,
            choices: [
              {
                index: 0,
                delta: {},
                finish_reason: finishReason(stopReason, toolCallIndexes.size > 0),
              },
            ],
          };
          if (usage) {
            finalPayload.usage = {
              prompt_tokens: usage.inputTokens,
              completion_tokens: usage.outputTokens,
              total_tokens: usage.inputTokens + usage.outputTokens,
              prompt_tokens_details: { cached_tokens: usage.cacheReadTokens },
              cache_write_tokens: usage.cacheWriteTokens,
            };
          }
          emit(finalPayload);
          controller.enqueue(TEXT_ENCODER.encode("data: [DONE]\n\n"));
        } catch (error) {
          try {
            await activeReader?.cancel("Devin Desktop Connect stream failed");
          } catch {
            // Preserve the original protocol/decode error below.
          }
          const safe = sanitizeErrorMessage(error instanceof Error ? error.message : String(error));
          emitError(`Devin Desktop stream error: ${safe}`);
        } finally {
          activeReader?.releaseLock();
          activeReader = null;
          controller.close();
        }
      },
      async cancel(reason) {
        await activeReader?.cancel(reason);
      },
    });

    return new Response(stream, {
      status: 200,
      headers: {
        "Content-Type": "text/event-stream",
        "Cache-Control": "no-cache",
        Connection: "keep-alive",
      },
    });
  }
}