重构: F-09 batch4 启用多会话上线(决策e真并发·F-09完整)

- IPC签名加conv_id: ai_is_generating/ai_chat_send/ai_chat_force_send/ai_chat_stop + 内部移除active一致性校验(后台conv可操作)
- 删switch readonly分支 + 删ai_conversation_create强制结束旧loop(决策e,切走旧loop不退出)
- 删双写桥接+顶层字段: messages/generating/stop_flag/notify/iteration_used/agent_language/model_override/session_trust全删,per_conv唯一真相源 + 删双写代码(全模块)+ 删fallback读 + pending_approvals retain目标conv
- 前端: api/ai.ts+useAiSend/useAiWindow传conv_id
保留: session_state(SW预留标allow)/readonly(前端不读);零调用方预留按用户指导保留
主代兜底: cargo check --workspace 0 + vue-tsc 0 + test 98 + grep顶层删除/per_conv唯一印证
F-09完整(batch1 PerConvState+batch2迁移+batch5限流调整+batch8恢复+batch4上线);双会话人工验收留用户

src-tauri/src/commands/ai/title.rs

@@ -43,47 +43,28 @@ pub(crate) async fn ensure_conversation_title(
     }
 
     // 取对话文本（仅 user/assistant，跳过 tool 噪音），取前 6 条供 LLM 总结
-    // F-260616-09 B 批2:读 per_conv.messages(conv_id 来源:本函数入参)。
-    //   per_conv 未建时 fallback 顶层(switch 触发的 spawn_ensure_title 可能无 per_conv)。
+    // F-260616-09 B 批4:per_conv.messages 唯一真相源(conv_id 来源:本函数入参)。
+    //   conv() 惰性建:switch 触发的 spawn_ensure_title 前序 switch 已 conv();若极端未建,
+    //   conv() 建空 PerConvState → summary_msgs 空 → 下方 return(无素材不生成标题)。
     let (summary_msgs, all_msgs) = {
-        let session = session_arc.lock().await;
-        let conv = session.conv_read(conv_id);
-        let summary: Vec<ChatMessage> = match conv {
-            Some(c) => c.messages.iter()
-                .filter(|m| matches!(m.role, MessageRole::User | MessageRole::Assistant))
-                .take(6)
-                .map(|m| ChatMessage {
-                    role: m.role.clone(),
-                    content: m.content.clone(),
-                    parts: None,
-                    tool_call_id: None,
-                    tool_calls: None,
-                    model: None,
-                    status: None,
-                    reasoning_content: m.reasoning_content.clone(),
-                    timestamp: m.timestamp,
-                })
-                .collect(),
-            None => session.messages.iter()
-                .filter(|m| matches!(m.role, MessageRole::User | MessageRole::Assistant))
-                .take(6)
-                .map(|m| ChatMessage {
-                    role: m.role.clone(),
-                    content: m.content.clone(),
-                    parts: None,
-                    tool_call_id: None,
-                    tool_calls: None,
-                    model: None,
-                    status: None,
-                    reasoning_content: m.reasoning_content.clone(),
-                    timestamp: m.timestamp,
-                })
-                .collect(),
-        };
-        let all_msgs = match conv {
-            Some(c) => c.messages.all_messages_clone(),
-            None => session.messages.all_messages_clone(),
-        };
+        let mut session = session_arc.lock().await;
+        let conv = session.conv(conv_id);
+        let summary: Vec<ChatMessage> = conv.messages.iter()
+            .filter(|m| matches!(m.role, MessageRole::User | MessageRole::Assistant))
+            .take(6)
+            .map(|m| ChatMessage {
+                role: m.role.clone(),
+                content: m.content.clone(),
+                parts: None,
+                tool_call_id: None,
+                tool_calls: None,
+                model: None,
+                status: None,
+                reasoning_content: m.reasoning_content.clone(),
+                timestamp: m.timestamp,
+            })
+            .collect();
+        let all_msgs = conv.messages.all_messages_clone();
         (summary, all_msgs)
     };
     if summary_msgs.is_empty() {