优化: sanitize 告警降级

- 修复告警 warn 降 debug,同份畸形历史每请求重复触发成洪水
- 涉 sanitize.rs 四处与 openai_compat 两处,含逐 orphan 单条刷屏点
- view-only 修复语义不变,存量配对清洗已完成

crates/df-ai/src/openai_compat.rs

@@ -424,7 +424,7 @@ fn sanitize_openai_triplets(messages: &mut Vec<OpenAiMessage>) {
         // 无配对头(id 不在任何保留 assistant 头内)→ orphan tool_result,丢弃。
         // 含两类:(a) assistant 头被 step2 剥后残留的 tool;(b) 全程无配对头的直构造/DB 残留。
         dropped_orphan_tools += 1;
-        tracing::warn!(
+        tracing::debug!(
             tool_call_id = %id,
             "[openai] orphan tool result(无配对 assistant tool_calls),已丢弃(防 'tool must be response to preceding tool_calls' 400)",
         );
@@ -432,7 +432,7 @@ fn sanitize_openai_triplets(messages: &mut Vec<OpenAiMessage>) {
     });
 
     if stripped_heads > 0 || dropped_orphan_tools > 0 {
-        tracing::warn!(
+        tracing::debug!(
             stripped_heads,
             total_stripped,
             dropped_orphan_tools,