新增: 消息级溯源 P2 切 ai_messages + AI Chat 跑题改进 P0-P2 + 标题诊断 + 苛刻测

消息级溯源 P2(一次性切读 b + 备份保留):
- 批次A 读路径切 ai_messages(state.rs AppState.ai_messages + 映射 ChatMessage↔AiMessageRecord +
  switch/export load 切 + fallback 兜底)
- 批次B 写路径切 ai_messages(replace_conversation 单事务全量重写 + save/clear 切 + 旧 messages 备份)
- 摘要/压缩不改 updated_at(save_conversation touch_updated_at,compress false 防时间分组跳变)

AI Chat 跑题改进 P0-P2(5 改进,治跑题 5 根因,三原则优雅/可靠/易迭代):
- P0 系统提示聚焦(## 聚焦准则独立段)+ 意图接入 loop(filter_tool_defs 收敛工具 29→5-10,三重 fallback)
- P1 压缩增强(compress prompt 主题锚点 + 失败关键词兜底 extract_keyword_summary)+
  工具结果压缩(should_summarize + extract_key_info view-only 不改持久化)
- P2 主题检测(TrackedMessage.topic + 双高置信保守标记 + tokenize 2-gram 修复中文锚点)
- title LLM complete 失败诊断日志(助定位返空根因)
- 跑题 P0 审查🟡修复(Debug 加 Data 域 + threshold 注释)

苛刻测 38 条(边界/对抗:全漂移/全停用词/全错误行/2KB 边界/连续主题切换/中文 2-gram/emoji)
df-ai 227 passed + workspace EXIT 0

src-tauri/src/state.rs

@@ -11,9 +11,9 @@ use tokio::sync::{Mutex, RwLock, Semaphore};
 
 use df_ai::ai_tools::AiToolRegistry;
 use df_storage::crud::{
-    AiConversationRepo, AiProviderRepo, AiToolExecutionRepo, IdeaRepo, KnowledgeEventsRepo,
-    KnowledgeRepo, NodeExecutionRepo, ProjectRepo, ReleaseRepo, SettingsRepo, TaskRepo,
-    WorkflowRepo,
+    AiConversationRepo, AiMessageRepo, AiProviderRepo, AiToolExecutionRepo, IdeaRepo,
+    KnowledgeEventsRepo, KnowledgeRepo, NodeExecutionRepo, ProjectRepo, ReleaseRepo,
+    SettingsRepo, TaskRepo, WorkflowRepo,
 };
 use df_storage::db::Database;
 use df_workflow::eventbus::EventBus;
@@ -261,6 +261,8 @@ pub struct AppState {
     pub ai_providers: AiProviderRepo,
     /// AI 对话历史 Repo
     pub ai_conversations: AiConversationRepo,
+    /// AI 消息 Repo(F-260619-03 消息拆分存储:ai_messages 表,读路径批次 A 切读用)
+    pub ai_messages: AiMessageRepo,
     /// AI 工具执行审计 Repo
     pub ai_tool_executions: AiToolExecutionRepo,
     /// AI 工具注册表
@@ -484,6 +486,7 @@ impl AppState {
             node_executions: NodeExecutionRepo::new(&db),
             ai_providers: AiProviderRepo::new(&db),
             ai_conversations: AiConversationRepo::new(&db),
+            ai_messages: AiMessageRepo::new(&db),
             ai_tool_executions: AiToolExecutionRepo::new(&db),
             ai_session: Arc::new(Mutex::new(AiSession::new())),
             knowledge: KnowledgeRepo::new(&db),