fix(protocol): normalize Anthropic's refusal stop reason when streaming

crates/protocol/src/stream.rs

@@ -506,7 +506,9 @@ fn stop_reason_from_str(reason: Option<&str>) -> StopReason {
     match reason {
         Some("length" | "max_tokens") => StopReason::MaxTokens,
         Some("tool_calls" | "function_call" | "tool_use") => StopReason::ToolUse,
-        Some("content_filter") => StopReason::ContentFilter,
+        // Anthropic spells a content-policy stop `refusal`; the buffered codec
+        // already maps it (anthropic/buffered.rs, map_anthropic_stop_reason).
+        Some("content_filter" | "refusal") => StopReason::ContentFilter,
         Some("stop" | "end_turn" | "stop_sequence") | None => StopReason::EndTurn,
         Some(_) => StopReason::Unknown,
     }
@@ -563,6 +565,33 @@ mod tests {
         );
     }
 
+    #[test]
+    fn stop_reason_spellings_normalize_the_same_streamed_as_buffered() {
+        // A stop reason has to mean the same thing whether the response arrived
+        // buffered or was folded out of a stream. The expectations here are the
+        // ones the codecs apply to a buffered body.
+        for (reason, expected) in [
+            ("length", StopReason::MaxTokens),
+            ("max_tokens", StopReason::MaxTokens),
+            ("tool_calls", StopReason::ToolUse),
+            ("tool_use", StopReason::ToolUse),
+            ("content_filter", StopReason::ContentFilter),
+            ("refusal", StopReason::ContentFilter),
+            ("stop", StopReason::EndTurn),
+            ("end_turn", StopReason::EndTurn),
+        ] {
+            let agg = fold(vec![LlmResponseChunk::MessageStop {
+                reason: Some(reason.to_string()),
+            }]);
+
+            assert_eq!(
+                agg.outputs.first().and_then(|output| output.stop_reason),
+                Some(expected),
+                "stop reason {reason:?}"
+            );
+        }
+    }
+
     #[test]
     fn aggregates_normalized_chunks_inside_stream_event() {
         let response = LlmResponse::Stream(Box::pin(stream::iter([Ok(