From cae4ebb89d6685e581259b5754c1fd4a565d95a3 Mon Sep 17 00:00:00 2001
From: Graham King <grahamk@nvidia.com>
Date: Tue, 22 Sep 2026 16:20:00 -0400
Subject: [PATCH] fix(anthropic): Include api_error type in stream error events

Previously `switchyard-server` emitted Anthropic SSE error events without the required nested `error.type`.

Fixes: https://linear.app/nvidia/issue/SWITCH-1548

Assisted-by: Pi:GPT 6 Astra medium
Reviewed-by: Claude:Opus 5.5 medium
Signed-off-by: Graham King <grahamk@nvidia.com>
---
 crates/switchyard-server/src/sse.rs           | 30 +++++++++++++-
 .../src/codecs/anthropic/stream.rs            |  2 +-
 .../tests/stream_translation.rs               | 39 +++++++++++++++++++
 3 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/crates/switchyard-server/src/sse.rs b/crates/switchyard-server/src/sse.rs
index e685ba5e5..10b526790 100644
--- a/crates/switchyard-server/src/sse.rs
+++ b/crates/switchyard-server/src/sse.rs
@@ -99,13 +99,18 @@ fn error_event(target_format: WireFormat, message: String, redactor: &Redactor)
             ),
         ),
         WireFormat::AnthropicMessages | WireFormat::OpenAiResponses => {
+            let error_type = if target_format == WireFormat::AnthropicMessages {
+                "api_error"
+            } else {
+                "SwitchyardError"
+            };
             Event::default().event("error").data(
                 redactor.json(
                     json!({
                         "type": "error",
                         "error": {
                             "message": message,
-                            "type": "SwitchyardError",
+                            "type": error_type,
                         }
                     })
                     .to_string(),
@@ -181,4 +186,27 @@ mod tests {
         assert!(!body.contains("[DONE]"));
         Ok(())
     }
+
+    #[tokio::test]
+    async fn anthropic_stream_error_uses_api_error_type() -> TestResult {
+        let failure = LlmClientError::General("boom".to_string());
+        let stream: RawEventStream =
+            Box::pin(stream::iter(vec![Err(LlmStreamError::Client(failure))]));
+        let response = frame_stream(
+            stream,
+            WireFormat::AnthropicMessages,
+            Arc::new(Redactor::default()),
+        )
+        .into_response();
+        let body = String::from_utf8(to_bytes(response.into_body(), usize::MAX).await?.to_vec())?;
+        let data = body
+            .lines()
+            .find_map(|line| line.strip_prefix("data: "))
+            .ok_or("missing data line")?;
+        assert_eq!(
+            serde_json::from_str::<Value>(data)?,
+            json!({"type": "error", "error": {"type": "api_error", "message": "boom"}})
+        );
+        Ok(())
+    }
 }
diff --git a/crates/switchyard-translation/src/codecs/anthropic/stream.rs b/crates/switchyard-translation/src/codecs/anthropic/stream.rs
index cc3955f9c..908941a89 100644
--- a/crates/switchyard-translation/src/codecs/anthropic/stream.rs
+++ b/crates/switchyard-translation/src/codecs/anthropic/stream.rs
@@ -242,7 +242,7 @@ fn encode_anthropic_stream(
             // An in-band error is terminal: emit the error, then nothing further.
             state.finished = true; // finish() adds no success events
             state.errored = true; // the entry guard drops any later chunk
-            vec![json!({"type": "error", "error": {"message": message}})]
+            vec![json!({"type": "error", "error": {"type": "api_error", "message": message}})]
         }
     }
 }
diff --git a/crates/switchyard-translation/tests/stream_translation.rs b/crates/switchyard-translation/tests/stream_translation.rs
index e22511c59..01e9cc0da 100644
--- a/crates/switchyard-translation/tests/stream_translation.rs
+++ b/crates/switchyard-translation/tests/stream_translation.rs
@@ -203,6 +203,45 @@ fn preserved_same_format_replay_stops_after_an_error() -> TestResult {
     Ok(())
 }
 
+#[test]
+fn anthropic_errors_include_type_and_terminate_stream() -> TestResult {
+    let engine = TranslationEngine::default();
+    let target = WireFormat::AnthropicMessages;
+    let message = "stream failed";
+    for chunk in [
+        LlmResponseChunk::StreamError {
+            message: message.into(),
+        },
+        LlmResponseChunk::DecodeError {
+            message: message.into(),
+        },
+    ] {
+        let mut state = StreamTranslationState::new(WireFormat::OpenAiChat, target);
+        let events = engine.encode_stream_event(
+            &mut state,
+            target,
+            LlmResponseStreamEvent::new(vec![chunk]),
+        )?;
+        assert_eq!(
+            events,
+            vec![json!({"type": "error", "error": {"type": "api_error", "message": message}})]
+        );
+        assert!(
+            engine
+                .encode_stream_event(
+                    &mut state,
+                    target,
+                    LlmResponseStreamEvent::new(vec![LlmResponseChunk::MessageStop {
+                        reason: None
+                    }]),
+                )?
+                .is_empty()
+        );
+        assert!(engine.finish_stream(&mut state, target)?.is_empty());
+    }
+    Ok(())
+}
+
 #[test]
 fn same_format_decode_failure_emits_terminal_error() -> TestResult {
     let cases = [