Add reply-to-message capability with ID-addressable history

Lets the bot quote-reply to a specific message via an optional replyTo
on sendSingleMessage, and reworks history serialization so the LLM can
address messages and stop confusing quoted content with the quoter.

- Serialize each history line with a short [n] id; consecutive messages
  from the same sender continue under "[n]  └". A per-subject ReplyIndex
  maps [n] -> MessageRecord, kept alive with the context cache so ids
  stay continuous across cached turns.
- Replace inlined quote text with a reference: "↩[k]" when the quoted
  message is in-window, otherwise "↩(author:"snippet…")". This removes
  the ambiguity where A quoting B looked like A's own speech.
- Collapse forwarded messages to "[转发消息·N条:title]".
- sendSingleMessage accepts replyTo (the [n]); it resolves the record via
  MessageRecord.toMessageSource() and prepends a QuoteReply, falling back
  to a plain send with a note if the source is gone. ids may be null, so
  numbering still happens but such records can't be reply targets.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/kotlin/tools/SendSingleMessageAgent.kt

@@ -4,6 +4,8 @@ import com.aallam.openai.api.chat.Tool
 import com.aallam.openai.api.core.Parameters
 import kotlinx.serialization.json.*
 import net.mamoe.mirai.event.events.MessageEvent
+import net.mamoe.mirai.message.data.Message
+import net.mamoe.mirai.message.data.QuoteReply
 import top.jie65535.mirai.JChatGPT
 
 class SendSingleMessageAgent : BaseAgent(
@@ -17,6 +19,10 @@ class SendSingleMessageAgent : BaseAgent(
                     put("type", "string")
                     put("description", "消息内容")
                 }
+                putJsonObject("replyTo") {
+                    put("type", "integer")
+                    put("description", "可选。要引用回复的历史消息编号（即历史记录中每行行首的[n]）。不需要回复具体某条消息时省略此参数。")
+                }
             }
             putJsonArray("required") {
                 add("content")
@@ -27,7 +33,28 @@ class SendSingleMessageAgent : BaseAgent(
     override suspend fun execute(args: JsonObject?, event: MessageEvent): String {
         requireNotNull(args)
         val content = args.getValue("content").jsonPrimitive.content
-        event.subject.sendMessage(JChatGPT.toMessage(event.subject, content))
-        return "OK"
+        val replyTo = args["replyTo"]?.jsonPrimitive?.intOrNull
+
+        val baseMsg = JChatGPT.toMessage(event.subject, content)
+        var note = ""
+        val message: Message = if (replyTo != null) {
+            val record = JChatGPT.lookupReplyTarget(event.subject.id, replyTo)
+            val source = try {
+                record?.toMessageSource()
+            } catch (e: Throwable) {
+                null
+            }
+            if (source != null) {
+                QuoteReply(source) + baseMsg
+            } else {
+                note = "（编号${replyTo}对应的消息已失效，未能引用，已直接发送）"
+                baseMsg
+            }
+        } else {
+            baseMsg
+        }
+
+        event.subject.sendMessage(message)
+        return "OK$note"
     }
-}
+}