Add chat endpoint failover for resilience against unstable LLM APIs

Configure a list of fallback chat endpoints (chatFallbacks); each blank
field inherits the primary, so you can swap just the API key, just the
model, or the whole vendor. On LLM streaming failure the retry loop
advances to the next endpoint, and a failed endpoint enters a cooldown
(fallbackCooldownMinutes) so a dead primary is skipped instead of
wasting a timeout on every message.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/main/kotlin/PluginConfig.kt

@@ -1,9 +1,22 @@
 package top.jie65535.mirai
 
+import kotlinx.serialization.Serializable
 import net.mamoe.mirai.console.data.AutoSavePluginConfig
 import net.mamoe.mirai.console.data.ValueDescription
 import net.mamoe.mirai.console.data.value
 
+/**
+ * 聊天模型备用接入点。用于主接入点（openAiApi/openAiToken/chatModel）连续失败时容灾切换。
+ * 任一字段留空则继承主接入点对应配置，因此可只换 API KEY、只换模型、或整体换一个服务商。
+ */
+@Serializable
+data class ChatFallbackEndpoint(
+    val api: String = "",
+    val token: String = "",
+    val model: String = "",
+    val extraBody: String = "",
+)
+
 object PluginConfig : AutoSavePluginConfig("Config") {
     @ValueDescription("主人QQ，AI可以通过工具向主人发起请求，会等待一段时间")
     val ownerId: Long by value()
@@ -41,6 +54,12 @@ object PluginConfig : AutoSavePluginConfig("Config") {
     @ValueDescription("聊天模型额外请求体JSON，会合并到请求体中。例如DeepSeek关闭思维: {\"thinking\": {\"type\": \"disabled\"}}")
     val chatModelExtraBody: String by value("")
 
+    @ValueDescription("聊天模型备用接入点列表（容灾）。主接入点连续失败时按顺序切换；每项留空的字段会继承主接入点，例如只换API KEY就只填token，只换模型就只填model")
+    val chatFallbacks: List<ChatFallbackEndpoint> by value()
+
+    @ValueDescription("备用接入点冷却时间（分钟）。某接入点失败后在此时间内会被排到重试队尾，避免每条消息都先卡在故障接入点上。设为0禁用，默认5分钟")
+    val fallbackCooldownMinutes: Long by value(5L)
+
     @ValueDescription("推理模型额外请求体JSON，会合并到请求体中。例如DeepSeek启用思维: {\"thinking\": {\"type\": \"enabled\"}}")
     val reasoningModelExtraBody: String by value("")