fix: download fallback URL when primary fails

- Gitea URL used as primary (same-version tie-break), GitHub as fallback
- download() tries base url first; if it fails, automatically retries
  the fallback URL
- version 1.9.1 -> 1.9.2 (code 30 -> 31)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/build.gradle.kts

@@ -13,8 +13,8 @@ android {
         applicationId = "com.a2i.forwarder"
         minSdk = 34
         targetSdk = 36
-        versionCode = 29
-        versionName = "1.9.0"
+        versionCode = 30
+        versionName = "1.9.1"
     }
 
     signingConfigs {

app/src/main/java/com/a2i/forwarder/core/UpdateChecker.kt

@@ -26,6 +26,7 @@ data class UpdateInfo(
     val apkSize: Long,
     val releaseNotes: String,
     val releasePageUrl: String,
+    val fallbackUrl: String? = null,   // 主 URL 下载失败时尝试的备选链接
 )
 
 /**
@@ -71,9 +72,12 @@ class UpdateChecker(private val context: Context) {
             // 先查 GitHub（公开默认源），从其 release notes 动态发现额外源（如自建 Gitea），取最高版本
             // 同版本时 Gitea 优先（国内可达，GitHub 可能被墙导致下载失败）
             val infos = mutableListOf<UpdateInfo>()
+            var ghInfo: UpdateInfo? = null
+            var giteaInfo: UpdateInfo? = null
             val gh = runCatching { fetchRelease(GITHUB_API) }.getOrNull()
             if (gh != null) {
-                val giteaInfo = parseUpdateSource(gh.releaseNotes)?.let { runCatching { fetchRelease(it) }.getOrNull() }
+                ghInfo = gh
+                giteaInfo = parseUpdateSource(gh.releaseNotes)?.let { runCatching { fetchRelease(it) }.getOrNull() }
                 // Gitea 放前面，同版本时优先用它下载（国内可达）
                 if (giteaInfo != null) infos.add(giteaInfo)
                 infos.add(gh)
@@ -92,7 +96,9 @@ class UpdateChecker(private val context: Context) {
                 updateInfo.value = null
                 lastNotifiedVersion = null
             } else {
-                updateInfo.value = best
+                // 主 URL 下载失败时尝试另一个源的链接
+                val fallback = if (best == giteaInfo) ghInfo?.apkUrl else giteaInfo?.apkUrl
+                updateInfo.value = best.copy(fallbackUrl = fallback)
             }
             lastError.value = null
 
@@ -179,14 +185,29 @@ class UpdateChecker(private val context: Context) {
         downloading.value = true
         downloadProgress.value = 0
         lastError.value = null
-        try {
-            val req = Request.Builder().url(info.apkUrl).get().build()
+        // 主 URL 失败时自动尝试备选 URL
+        val urls = listOf(info.apkUrl) + (info.fallbackUrl?.let { listOf(it) } ?: emptyList())
+        for ((idx, url) in urls.withIndex()) {
+            if (idx > 0) downloadProgress.value = 0  // 重试时重置进度
+            val file = tryDownload(url, info.latestVersion)
+            if (file != null) {
+                downloading.value = false
+                return@withContext file
+            }
+        }
+        downloading.value = false
+        null
+    }
+
+    private suspend fun tryDownload(url: String, version: String): File? {
+        return try {
+            val req = Request.Builder().url(url).get().build()
             http.newCall(req).execute().use { res ->
-                if (!res.isSuccessful) { lastError.value = "HTTP ${res.code}"; return@use null }
-                val body = res.body ?: run { lastError.value = "空响应"; return@use null }
+                if (!res.isSuccessful) { lastError.value = "HTTP ${res.code}"; return@tryDownload null }
+                val body = res.body ?: run { lastError.value = "空响应"; return@tryDownload null }
                 val total = body.contentLength()
                 val dir = context.getExternalFilesDir(null) ?: context.cacheDir
-                val target = File(dir, "gotmsg-${info.latestVersion}.apk")
+                val target = File(dir, "gotmsg-${version}.apk")
                 target.outputStream().use { sink ->
                     val input = body.byteStream()
                     val buf = ByteArray(8 * 1024)
@@ -205,8 +226,6 @@ class UpdateChecker(private val context: Context) {
         } catch (e: Exception) {
             lastError.value = e.message ?: "下载失败"
             null
-        } finally {
-            downloading.value = false
         }
     }