fix: persist model on conversation send, fallback resolution, carry model on new conversation

apps/desktop/Cargo.toml

@@ -29,6 +29,7 @@ reqwest.workspace = true
 futures.workspace = true
 uuid.workspace = true
 dirs.workspace = true
+rusqlite.workspace = true
 xianren-core = { path = "../../crates/core" }
 xianren-engine = { path = "../../crates/engine" }
 xianren-download = { path = "../../crates/download" }

apps/desktop/src/commands.rs

@@ -217,10 +217,12 @@ pub fn list_conversations(state: State<'_, App>) -> Result<Vec<xianren_core::Con
 pub fn create_conversation(
     state: State<'_, App>,
     title: String,
+    model_id: Option<String>,
 ) -> Result<xianren_core::Conversation, String> {
     let id = uuid::Uuid::new_v4().to_string();
     let db = state.core.db.lock().unwrap();
-    sessions_db::create_conversation(&db, &id, &title, None, None).map_err(|e| e.to_string())?;
+    sessions_db::create_conversation(&db, &id, &title, model_id.as_deref(), None)
+        .map_err(|e| e.to_string())?;
     sessions_db::get_conversation(&db, &id)
         .map_err(|e| e.to_string())?
         .ok_or_else(|| "conversation not found".to_string())
@@ -481,6 +483,9 @@ pub async fn chat_send(
             )
             .map_err(|e| e.to_string())?;
         }
+        // 始终把当前使用的模型写回会话，编辑/重新生成依赖它
+        sessions_db::update_conversation_model(&db, &payload.conversation_id, &payload.model_id)
+            .map_err(|e| e.to_string())?;
         let user_message_id = sessions_db::add_message(
             &db,
             &payload.conversation_id,
@@ -724,6 +729,21 @@ fn estimate_tokens(text: &str) -> usize {
     score / 4 + 1
 }
 
+/// 解析会话使用的模型：优先会话记录；未记录时若本地只有一个模型则自动使用，否则提示。
+fn resolve_conversation_model(
+    db: &rusqlite::Connection,
+    conversation: &xianren_core::Conversation,
+) -> Result<String, String> {
+    if let Some(id) = &conversation.model_id {
+        return Ok(id.clone());
+    }
+    let all = models_db::list(db).map_err(|e| e.to_string())?;
+    if all.len() == 1 {
+        return Ok(all[0].id.clone());
+    }
+    Err("会话未记录模型：请先在该会话发送一条消息，或重新选择模型后重试".into())
+}
+
 /// 重新生成某条助手回复：旧内容存入版本历史，截断后重新生成。
 #[tauri::command]
 pub async fn regenerate_message(
@@ -768,10 +788,7 @@ pub async fn regenerate_message(
                 images: m.images.clone(),
             })
             .collect::<Vec<_>>();
-        let model_id = conversation
-            .model_id
-            .clone()
-            .ok_or_else(|| "conversation has no model".to_string())?;
+        let model_id = resolve_conversation_model(&db, &conversation)?;
         let model = models_db::get(&db, &model_id)
             .map_err(|e| e.to_string())?
             .ok_or_else(|| "model not found".to_string())?;
@@ -835,10 +852,7 @@ pub async fn edit_message(
                 images: m.images,
             })
             .collect::<Vec<_>>();
-        let model_id = conversation
-            .model_id
-            .clone()
-            .ok_or_else(|| "conversation has no model".to_string())?;
+        let model_id = resolve_conversation_model(&db, &conversation)?;
         let model = models_db::get(&db, &model_id)
             .map_err(|e| e.to_string())?
             .ok_or_else(|| "model not found".to_string())?;