fix(anthropic): accept done stream terminator

crates/switchyard-components/src/backends/anthropic.rs

@@ -524,9 +524,10 @@ fn anthropic_sse_stream(response: reqwest::Response) -> BoxResponseStream {
             // Anthropic SSE has named events, but the payload we care about is
             // still the JSON `data:` line.
             while let Some(frame) = drain_next_sse_frame(&mut buffer, "Anthropic")? {
-                match parse_json_sse_frame(&frame, "Anthropic", None)? {
+                match parse_json_sse_frame(&frame, "Anthropic", Some("[DONE]"))? {
                     ParsedSseFrame::Json(value) => yield StreamEvent::Json(value),
-                    ParsedSseFrame::Done | ParsedSseFrame::Empty => {}
+                    ParsedSseFrame::Done => return,
+                    ParsedSseFrame::Empty => {}
                 }
             }
         }
@@ -535,7 +536,7 @@ fn anthropic_sse_stream(response: reqwest::Response) -> BoxResponseStream {
         // separator.
         if has_non_whitespace_bytes(&buffer) {
             let frame = decode_sse_frame(&buffer, "Anthropic")?;
-            match parse_json_sse_frame(&frame, "Anthropic", None)? {
+            match parse_json_sse_frame(&frame, "Anthropic", Some("[DONE]"))? {
                 ParsedSseFrame::Json(value) => yield StreamEvent::Json(value),
                 ParsedSseFrame::Done | ParsedSseFrame::Empty => {}
             }

crates/switchyard-components/tests/adversarial_native_backends.rs

@@ -1040,6 +1040,42 @@ async fn anthropic_streaming_returns_stream_events() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn anthropic_streaming_stops_at_done_marker() -> Result<()> {
+    let server = OneShotServer::sse(
+        "event: message_start\n\
+         data: {\"type\":\"message_start\",\"message\":{\"id\":\"msg-stream\"}}\n\n\
+         data: [DONE]\n\n\
+         event: message_stop\n\
+         data: {\"type\":\"message_stop\"}\n\n",
+    )?;
+    let backend = AnthropicNativeBackend::new(anthropic_target(server.base_url().to_string())?)?;
+    let mut ctx = ProxyContext::new();
+
+    let response = backend
+        .call(
+            &mut ctx,
+            &ChatRequest::anthropic(json!({
+                "model": "client-claude",
+                "max_tokens": 128,
+                "messages": [{"role": "user", "content": "stream"}],
+                "stream": true
+            })),
+        )
+        .await?;
+    let events = collect_json_events(response).await?;
+    server.captured()?;
+
+    assert_eq!(
+        events,
+        vec![json!({
+            "type": "message_start",
+            "message": {"id": "msg-stream"}
+        })]
+    );
+    Ok(())
+}
+
 // Anthropic native must reject targets configured for OpenAI format.
 #[test]
 fn anthropic_backend_rejects_openai_targets() -> Result<()> {