fix: flush direct SSE proxy frames before completion

tests/test_tracker_routing.py

@@ -635,6 +635,7 @@ def test_tracker_dashboard_can_cancel_inflight_proxy():
     "Tracker dashboard can cancel inflight proxy\n\nTags: http, routing, tracker"
     chunk_sent = threading.Event()
     release = threading.Event()
+    upstream_finished = threading.Event()
 
     class StreamingChatHandler(http.server.BaseHTTPRequestHandler):
         def log_message(self, fmt, *args):
@@ -655,9 +656,10 @@ def test_tracker_dashboard_can_cancel_inflight_proxy():
             self.wfile.write(b"data: " + payload + b"\n\n")
             self.wfile.flush()
             chunk_sent.set()
-            release.wait(timeout=3.0)
+            release.wait()
             self.wfile.write(b"data: [DONE]\n\n")
             self.wfile.flush()
+            upstream_finished.set()
 
     node = http.server.HTTPServer(("127.0.0.1", 0), StreamingChatHandler)
     node_thread = threading.Thread(target=node.serve_forever, daemon=True)
@@ -677,6 +679,7 @@ def test_tracker_dashboard_can_cancel_inflight_proxy():
         req = urllib.request.Request(
             f"http://127.0.0.1:{tracker_port}/v1/chat/completions",
             data=json.dumps({
+                "id": "direct-sse-cancel",
                 "model": "cancel-proxy-model",
                 "stream": True,
                 "messages": [{"role": "user", "content": "hi"}],
@@ -688,14 +691,8 @@ def test_tracker_dashboard_can_cancel_inflight_proxy():
         first_line = response.readline()
         assert first_line.startswith(b"data:")
         assert chunk_sent.wait(timeout=1.0)
-
-        console = _get_json(f"http://127.0.0.1:{tracker_port}/v1/console")
-        selected = [
-            event for event in console["events"]
-            if event["message"] == "proxy route selected"
-        ]
-        assert selected
-        request_id = selected[-1]["fields"]["request_id"]
+        assert not upstream_finished.is_set()
+        request_id = "direct-sse-cancel"
 
         cancel = _post_json(
             f"http://127.0.0.1:{tracker_port}/v1/proxy/requests/{urllib.parse.quote(request_id, safe='')}/cancel",
@@ -703,19 +700,27 @@ def test_tracker_dashboard_can_cancel_inflight_proxy():
         )
         assert cancel["status"] == "canceled"
 
-        deadline = time.time() + 5.0
-        canceled_events = []
-        while time.time() < deadline:
-            console = _get_json(f"http://127.0.0.1:{tracker_port}/v1/console")
-            canceled_events = [
-                event for event in console["events"]
-                if event["message"] == "proxy canceled"
-                and event["fields"].get("request_id") == request_id
-            ]
-            if canceled_events:
-                break
-            time.sleep(0.05)
+        # Chunked SSE termination makes this return as soon as the tracker has
+        # observed cancellation, rather than blocking on the held upstream. The
+        # only bytes that may still arrive are the blank-line terminator of the
+        # already-relayed first frame; the upstream's held "[DONE]" must never
+        # reach the client, and the upstream must still be blocked mid-stream.
+        remainder = response.read()
+        assert b"[DONE]" not in remainder
+        assert remainder.strip() == b""
+        assert not upstream_finished.is_set()
+        console = _get_json(f"http://127.0.0.1:{tracker_port}/v1/console")
+        canceled_events = [
+            event for event in console["events"]
+            if event["message"] == "proxy canceled"
+            and event["fields"].get("request_id") == request_id
+        ]
         assert canceled_events
+        assert len(canceled_events) == 1
+        assert tracker._server is not None
+        assert request_id not in tracker._server.active_proxies
+        registered = next(iter(tracker._server.registry.values()))
+        assert registered.proxy_inflight == 0
     finally:
         release.set()
         if response is not None: