fix: derive Windows image keys from local metadata

src/shared/wechat-image-key-derivation.ts

@@ -0,0 +1,35 @@
+import crypto from 'crypto'
+
+export type DerivedV4ImageKeys = { xorKey: number; aesKey: string }
+
+export function normalizeV4AccountId(value: string): string {
+  const leaf = String(value || '')
+    .trim()
+    .split(/[\\/]/)
+    .filter(Boolean)
+    .pop()
+  if (!leaf) return ''
+  const wxid = leaf.match(/^(wxid_[^_]+)/i)
+  if (wxid) return wxid[1]
+  return leaf.replace(/_[a-z0-9]{4}$/i, '')
+}
+
+export function extractKvcommCode(fileName: string): number | null {
+  const match = String(fileName || '').match(/^key_(\d+)_.+\.statistic$/i)
+  if (!match) return null
+  const code = Number.parseInt(match[1], 10)
+  if (!Number.isSafeInteger(code) || code <= 0 || code > 0xffffffff) return null
+  return code
+}
+
+export function deriveV4ImageKeys(code: number, accountId: string): DerivedV4ImageKeys | null {
+  const normalizedAccountId = normalizeV4AccountId(accountId)
+  if (!Number.isSafeInteger(code) || code <= 0 || code > 0xffffffff || !normalizedAccountId) {
+    return null
+  }
+  const digest = crypto
+    .createHash('md5')
+    .update(`${code}${normalizedAccountId}`, 'utf8')
+    .digest('hex')
+  return { xorKey: code & 0xff, aesKey: digest.slice(0, 16) }
+}