feat: push chart tail candles over SSE for faster market refresh

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_hub_chart_cache.py

@@ -35,6 +35,43 @@ class TestHubChartCache(unittest.TestCase):
         self.assertIn(series_key("okx_auto", "BTC/USDT", "5m"), keys)
         self.assertIn(series_key("gate_trend", "HYPE/USDT", "5m"), keys)
 
+    def test_note_series_result_pushes_tail_candles(self) -> None:
+        store = ChartPollStore()
+        key = series_key("binance", "BTC/USDT", "15m")
+        candles = [
+            {"time": 1_700_000_000 + i * 900, "open": 1, "high": 2, "low": 0.5, "close": 1.5, "volume": 10}
+            for i in range(40)
+        ]
+        store.note_series_result(
+            "binance",
+            "BTC/USDT",
+            "15m",
+            ok=True,
+            fetched=3,
+            candles=candles,
+            price_tick=0.01,
+        )
+        ev = store.event_dict()
+        self.assertIn("tails", ev)
+        self.assertIn(key, ev["tails"])
+        tail = ev["tails"][key]
+        self.assertEqual(len(tail["candles"]), 30)
+        self.assertEqual(tail["price_tick"], 0.01)
+        self.assertGreater(tail["series_version"], 0)
+
+    def test_broadcast_clears_pending_tails(self) -> None:
+        store = ChartPollStore()
+        store.note_series_result(
+            "gate",
+            "ONDO/USDT",
+            "5m",
+            ok=True,
+            candles=[{"time": 100, "open": 1, "high": 1, "low": 1, "close": 1, "volume": 1}],
+        )
+        store._broadcast()
+        ev = store.event_dict()
+        self.assertNotIn("tails", ev)
+
     def test_poll_increments_version(self) -> None:
         async def run() -> None:
             store = ChartPollStore()