修复: 上下文流式与工具签名域清债

- tool_signature 归一化补参,合法换参不再误触探索熔断
- SSE 超限截头改对齐事件边界保尾,流不再永久破损
- content_filter 纳入终态判定,无 DONE 流也收敛
- sanitize 占位补头前缀短路只吞 orphan 的盲区消除
- intent 关键词加词边界,history 不再误判
- 恢复重放后重置话题锚点,URL 图 token 地板不被稀释

crates/df-ai/src/openai_helpers.rs

@@ -191,6 +191,10 @@ impl From<OpenAiUsageRaw> for OpenAiUsage {
 /// SSE 流式响应 chunk
 #[derive(Debug, Deserialize)]
 pub(crate) struct OpenAiStreamChunk {
+    /// 流式 choice 数组。标准 error 帧(`{"error":{..}}`)与 usage 尾帧均不带 choices 键,
+    /// 缺省为空数组才能整帧解析成功;必填会让这类合法帧 serde 失败走空 chunk 分支,
+    /// 流呈无声截断。
+    #[serde(default)]
     pub choices: Vec<OpenAiStreamChoice>,
     /// 末 chunk（choices 为空）携带的累计 usage
     #[serde(default)]
@@ -204,11 +208,13 @@ pub(crate) struct OpenAiStreamChunk {
 
 #[derive(Debug, Deserialize)]
 pub(crate) struct OpenAiStreamChoice {
+    /// 部分 usage 尾帧的 choice 仅带 finish_reason 无 delta 键,缺省按空 delta 处理
+    #[serde(default)]
     pub delta: OpenAiStreamDelta,
     pub finish_reason: Option<String>,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Default, Deserialize)]
 pub(crate) struct OpenAiStreamDelta {
     pub content: Option<String>,
     pub tool_calls: Option<Vec<OpenAiStreamToolCall>>,
@@ -219,6 +225,8 @@ pub(crate) struct OpenAiStreamDelta {
 
 #[derive(Debug, Deserialize)]
 pub(crate) struct OpenAiStreamToolCall {
+    /// 部分端点 tool_call 增量省略 index,缺省 0(单工具调用场景语义等价)
+    #[serde(default)]
     pub index: u32,
     pub id: Option<String>,
     pub function: Option<OpenAiStreamFunction>,
@@ -299,10 +307,13 @@ pub(crate) fn apply_openai_sse(data: &str, usage_accum: &mut Option<TokenUsage>)
             }
             if let Some(choice) = chunk.choices.into_iter().next() {
                 let delta_text = choice.delta.content.unwrap_or_default();
-                // "length" = max_tokens 截断，属正常终止（非断连），纳入 finished
-                let finished = choice.finish_reason.as_deref() == Some("stop")
-                    || choice.finish_reason.as_deref() == Some("tool_calls")
-                    || choice.finish_reason.as_deref() == Some("length");
+                // 终态 finish_reason：stop（正常结束）/ tool_calls（转交工具执行）/
+                // length（max_tokens 截断，属正常终止非断连）/ content_filter（内容审查拦截）。
+                // content_filter 的流部分 provider 不发 [DONE] 帧，不纳入终态会一直悬挂
+                let finished = matches!(
+                    choice.finish_reason.as_deref(),
+                    Some("stop") | Some("tool_calls") | Some("length") | Some("content_filter")
+                );
 
                 let tool_calls = choice.delta.tool_calls.map(|tcs| {
                     tcs.into_iter()
@@ -411,4 +422,21 @@ mod tests {
         assert_eq!(usage.prompt_cache_hit_tokens, 64);
         assert_eq!(usage.prompt_cache_miss_tokens, 36);
     }
+
+    /// content_filter 属终态:敏感内容拦截的流部分 provider 不发 [DONE] 帧,
+    /// 必须靠 finish_reason 收敛,否则悬挂;未列入终态的 finish_reason 保持非终态
+    #[test]
+    fn finish_reason_content_filter_is_terminal() {
+        let data = r#"{"choices":[{"delta":{"content":""},"finish_reason":"content_filter"}]}"#;
+        let mut accum = None;
+        let chunk = apply_openai_sse(data, &mut accum);
+        assert!(chunk.finished, "content_filter 应收敛为终态,不再悬挂");
+
+        let mut accum2 = None;
+        let chunk2 = apply_openai_sse(
+            r#"{"choices":[{"delta":{"content":"x"},"finish_reason":null}]}"#,
+            &mut accum2,
+        );
+        assert!(!chunk2.finished, "无终态 finish_reason 的普通 delta 不应终结");
+    }
 }