重构: F-09批2 调用方迁移per-conv(双写桥接共存期)

- agentic.rs: GeneratingGuard加conv_id + 三处退出校验改conv存在性(决策e) + stop_flag/notify/messages/iteration per-conv + try_continue加conv_id参数
- commands.rs: IPC写路径双写桥接(per_conv新真相源+顶层双写,批4删) + ai_is_generating读per_conv fallback顶层
- audit/conversation/title/knowledge_inject/lib.rs: per_conv读写迁移
- conv()/conv_read()去allow(批2有调用方)
共存期双写: per_conv主+顶层双写兼容批4前IPC,批4签名改后删顶层
主代兜底: cargo check --workspace 0 + test 96 passed + grep三处退出/GeneratingGuard/双写印证

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

@@ -250,7 +250,15 @@ pub(crate) async fn maybe_spawn_extraction(
         return Ok(());
     }
     // 消息数守卫(总消息数,含 system/assistant/tool)
-    let msg_count = session_arc.lock().await.messages.len();
+    // F-260616-09 B 批2:读 per_conv.messages.len()(conv_id 来源:本函数入参)。
+    //   per_conv 未建时 fallback 顶层 messages.len()(同锁内取,避免双锁死锁)。
+    let msg_count = {
+        let session = session_arc.lock().await;
+        match session.conv_read(conv_id) {
+            Some(c) => c.messages.len(),
+            None => session.messages.len(),
+        }
+    };
     if (msg_count as u32) < config.min_messages {
         return Ok(());
     }