修复: aichat P2确定性bug批(audit吞错落日志+switch/delete占位终态化)

finalize: audit_tool_call insert 用 let _ = 吞 DB 错改 match Err tracing::error(对齐 audit_finalize:82模式,控制流不变不阻断,审计写失败落日志可确诊)
conversation+chat: switch/delete retain pending 前补 finalize_pending_placeholders 占位终态化(对齐 stop/clear/force_send,防占位 tool_result 残留下次发送喂 LLM);chat.rs finalize_pending_placeholders 可见性 fn→pub(crate)
cargo check --workspace 零错

src-tauri/src/commands/ai/audit/finalize.rs

@@ -32,7 +32,7 @@ pub(crate) async fn audit_tool_call(
     message_id: Option<&str>,
 ) {
     let executed_at = if decided_by.is_some() { Some(now_millis()) } else { None };
-    let _ = repo
+    if let Err(e) = repo
         .insert(AiToolExecutionRecord {
             id: new_id(),
             conversation_id: Some(conv_id.to_string()),
@@ -51,7 +51,16 @@ pub(crate) async fn audit_tool_call(
             executed_at,
             decided_by: decided_by.map(|s| s.to_string()),
         })
-        .await;
+        .await
+    {
+        tracing::error!(
+            "audit_tool_call: 写审计记录失败(conv={}, tool_call_id={}, tool={}): {}",
+            conv_id,
+            tool_call_id,
+            tool_name,
+            e
+        );
+    }
 }
 
 /// 审批后更新审计记录状态（按 tool_call_id 定位 pending 记录，回填 status/decided_by=human/executed_at/result）