重构会话管理功能，由后端 opencode 发放 sessionId，后端做 scope

src/routes/chatSession.ts

@@ -1,4 +1,5 @@
 import { logger } from "../logger.js";
+import { type SessionTurnRecord } from "../history/store.js";
 import { MemoryStore } from "../memory/store.js";
 import { type OpencodeRuntimeAdapter } from "../runtime/opencode.js";
 
@@ -8,6 +9,9 @@ const TITLE_PROMPT_TIMEOUT_MS = 5000;
 const TITLE_CONTEXT_MESSAGE_LIMIT = 40;
 const TITLE_CONTEXT_CHAR_LIMIT = 2400;
 const TITLE_CONTEXT_MESSAGE_CHAR_LIMIT = 240;
+const RESTORE_TURN_LIMIT = 8;
+const RESTORE_MESSAGE_CHAR_LIMIT = 480;
+const RESTORE_CONTEXT_CHAR_LIMIT = 3200;
 
 const buildSessionTitle = (message: string) => {
   const normalized = message.replace(/\s+/g, " ").trim();
@@ -155,11 +159,51 @@ export const buildPromptWithLearningContext = async (
   memoryStore: MemoryStore,
   actorKey: string,
   projectKey: string,
+  recentTurns: SessionTurnRecord[],
   message: string,
 ) => {
   const snapshot = await memoryStore.buildPromptSnapshot({ actorKey, projectKey });
-  if (!snapshot) {
+  const restoredConversation = buildRestoredConversationContext(recentTurns);
+  if (!snapshot && !restoredConversation) {
     return message;
   }
-  return `${snapshot}\n\n[Current user request]\n${message}`;
+  return [snapshot, restoredConversation, `[Current user request]\n${message}`]
+    .filter(Boolean)
+    .join("\n\n");
+};
+
+const buildRestoredConversationContext = (recentTurns: SessionTurnRecord[]) => {
+  const formattedTurns = recentTurns
+    .slice(-RESTORE_TURN_LIMIT)
+    .flatMap((turn) => [
+      `用户：${compactMessage(turn.userMessage)}`,
+      `助手：${compactMessage(turn.assistantMessage)}`,
+    ])
+    .filter((entry) => entry.length > 0);
+
+  if (formattedTurns.length === 0) {
+    return "";
+  }
+
+  const conversation = formattedTurns.join("\n");
+  const trimmedConversation =
+    conversation.length > RESTORE_CONTEXT_CHAR_LIMIT
+      ? `${conversation.slice(0, RESTORE_CONTEXT_CHAR_LIMIT - 3)}...`
+      : conversation;
+
+  return [
+    "[Previous conversation context]",
+    "以下为当前前端对话线程中最近的历史对话，请延续其中已确认的目标、约束、结论与引用结果。",
+    trimmedConversation,
+  ].join("\n");
+};
+
+const compactMessage = (value: string) => {
+  const normalized = value.replace(/\s+/g, " ").trim();
+  if (!normalized) {
+    return "";
+  }
+  return normalized.length > RESTORE_MESSAGE_CHAR_LIMIT
+    ? `${normalized.slice(0, RESTORE_MESSAGE_CHAR_LIMIT - 3)}...`
+    : normalized;
 };