Add constants and X-Msh-* header builder with persistent ~/.kimi/device_id

src/constants.ts

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+// Values mirror kimi-cli v1.35.0 1:1. When upstream bumps, update here and
+// nothing else in the codebase should hard-code these strings.
+//
+// Source of truth: research/kimi-cli/src/kimi_cli/constant.py,
+// research/kimi-cli/src/kimi_cli/auth/oauth.py
+//
+// NOTE: client_id is a public constant shipped inside the official CLI, not a
+// secret. scope `kimi-code` is what routes the issued JWT to K2.6.
+
+export const KIMI_CLI_VERSION = "1.35.0"
+export const USER_AGENT = `KimiCodeCLI/${KIMI_CLI_VERSION}`
+
+export const OAUTH_HOST = "https://auth.kimi.com"
+export const OAUTH_DEVICE_AUTH_URL = `${OAUTH_HOST}/api/oauth/device_authorization`
+export const OAUTH_TOKEN_URL = `${OAUTH_HOST}/api/oauth/token`
+export const OAUTH_CLIENT_ID = "17e5f671-d194-4dfb-9706-5516cb48c098"
+export const OAUTH_SCOPE = "kimi-code"
+export const OAUTH_DEVICE_GRANT = "urn:ietf:params:oauth:grant-type:device_code"
+export const OAUTH_REFRESH_GRANT = "refresh_token"
+
+export const API_BASE_URL = "https://api.kimi.com/coding/v1"
+export const MODEL_ID = "kimi-for-coding"
+
+// Refresh a bit before the server-reported expiry so we never race it.
+export const REFRESH_SAFETY_WINDOW_MS = 60_000

src/headers.ts

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+import os from "node:os"
+import fs from "node:fs"
+import path from "node:path"
+import crypto from "node:crypto"
+import { KIMI_CLI_VERSION, USER_AGENT } from "./constants.ts"
+
+// kimi-cli persists its device id at `~/.kimi/device_id` as a plain UUIDv4
+// hex string (no dashes). We intentionally share the same path so users who
+// also run the real kimi CLI keep a single stable fingerprint. See
+// research/kimi-cli/src/kimi_cli/auth/oauth.py (get_device_id).
+const DEVICE_ID_DIR = path.join(os.homedir(), ".kimi")
+const DEVICE_ID_PATH = path.join(DEVICE_ID_DIR, "device_id")
+
+function ensureDir(dir: string) {
+  if (!fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true, mode: 0o700 })
+}
+
+export function getDeviceId(): string {
+  ensureDir(DEVICE_ID_DIR)
+  if (fs.existsSync(DEVICE_ID_PATH)) {
+    const existing = fs.readFileSync(DEVICE_ID_PATH, "utf8").trim()
+    if (existing) return existing
+  }
+  const id = crypto.randomUUID().replace(/-/g, "")
+  fs.writeFileSync(DEVICE_ID_PATH, id, { mode: 0o600 })
+  return id
+}
+
+// Non-ASCII characters in HTTP headers will be rejected by Node's undici
+// fetch (`TypeError: Invalid character in header content`). kimi-cli does the
+// same sanitization in oauth._ascii_header_value.
+function ascii(value: string): string {
+  return value.replace(/[^\x20-\x7e]/g, "?")
+}
+
+/** Builds the 7 X-Msh-* / UA headers kimi-cli sends on every request. */
+export function kimiHeaders(): Record<string, string> {
+  return {
+    "User-Agent": USER_AGENT,
+    "X-Msh-Platform": "kimi_cli",
+    "X-Msh-Version": KIMI_CLI_VERSION,
+    "X-Msh-Device-Name": ascii(os.hostname() || "unknown"),
+    "X-Msh-Device-Model": ascii(os.machine?.() || os.arch()),
+    "X-Msh-Device-Id": getDeviceId(),
+    "X-Msh-Os-Version": ascii(`${os.type()} ${os.release()}`),
+  }
+}