fix(android): 修正下载URL解析和CookieManager线程

- 解析相对下载地址时使用 HOME_URL 域名根路径，避免把当前对话路径拼进URL

- CookieManager.getCookie 在主线程调用后再传入IO线程

android-webview-app/app/src/main/java/com/cyjai/agent/MainActivity.kt

@@ -544,7 +544,12 @@ class MainActivity : AppCompatActivity() {
                     Toast.makeText(this@MainActivity, "正在下载：$fileName", Toast.LENGTH_SHORT).show()
                 }
 
-                val downloadedFile = downloadFileToAppDir(absoluteUrl, fileName)
+                // CookieManager 必须在主线程访问
+                val cookie = withContext(Dispatchers.Main) {
+                    CookieManager.getInstance().getCookie(absoluteUrl)
+                }
+
+                val downloadedFile = downloadFileToAppDir(absoluteUrl, fileName, cookie)
 
                 withContext(Dispatchers.Main) {
                     shareDownloadedFile(downloadedFile)
@@ -563,13 +568,13 @@ class MainActivity : AppCompatActivity() {
         }
     }
 
-    private fun downloadFileToAppDir(urlString: String, preferredName: String): File {
+    private fun downloadFileToAppDir(urlString: String, preferredName: String, cookie: String?): File {
         val dir = File(filesDir, "downloads").apply { mkdirs() }
         val connection = URL(urlString).openConnection() as HttpURLConnection
         connection.connectTimeout = 30000
         connection.readTimeout = 30000
         connection.instanceFollowRedirects = true
-        connection.setRequestProperty("Cookie", CookieManager.getInstance().getCookie(urlString) ?: "")
+        connection.setRequestProperty("Cookie", cookie ?: "")
         connection.connect()
 
         val finalUrl = connection.url.toString()
@@ -621,12 +626,10 @@ class MainActivity : AppCompatActivity() {
 
     private fun resolveAbsoluteUrl(rawUrl: String): String {
         if (rawUrl.startsWith("http://") || rawUrl.startsWith("https://")) return rawUrl
-        val base = webView.url?.takeIf { it.startsWith("http://") || it.startsWith("https://") } ?: HOME_URL
-        return if (rawUrl.startsWith("/")) {
-            base.substringBefore("?").trimEnd('/') + rawUrl
-        } else {
-            base.trimEnd('/') + "/" + rawUrl
-        }
+        // API 始终位于域名根路径，不能拿当前 WebView URL（可能包含对话路径 /conv_id）作为 base，
+        // 否则会把 /api/download/file 拼到对话路径后面，导致 404。
+        val base = HOME_URL.trimEnd('/')
+        return if (rawUrl.startsWith("/")) "$base$rawUrl" else "$base/$rawUrl"
     }
 
     inner class ThemeBridge {