fix: gainers/losers binance fallback chain

backend/routers/expanded_market_api.py

@@ -118,6 +118,47 @@ async def _fetch_markets_from_coincap(limit: int) -> List[dict]:
     return rows
 
 
+async def _fetch_markets_from_binance(limit: int) -> List[dict]:
+    """Binance 24h ticker — reliable fallback when aggregators rate-limit."""
+    try:
+        async with httpx.AsyncClient(timeout=12.0) as client:
+            response = await client.get("https://api.binance.com/api/v3/ticker/24hr")
+            response.raise_for_status()
+            tickers = response.json()
+    except Exception as e:
+        logger.error(f"Binance movers error: {e}")
+        return []
+
+    rows: List[dict] = []
+    for item in tickers:
+        symbol = str(item.get("symbol", ""))
+        if not symbol.endswith("USDT"):
+            continue
+        try:
+            change = float(item.get("priceChangePercent", 0))
+            price = float(item.get("lastPrice", 0))
+            volume = float(item.get("quoteVolume", 0))
+        except (TypeError, ValueError):
+            continue
+        if price <= 0:
+            continue
+        base = symbol[:-4]
+        rows.append(
+            _normalize_market_row(
+                {
+                    "id": base.lower(),
+                    "symbol": base,
+                    "name": base,
+                    "priceUsd": price,
+                    "changePercent24Hr": change,
+                    "volumeUsd24Hr": volume,
+                },
+                "binance",
+            )
+        )
+    return rows[: max(limit * 3, 100)]
+
+
 async def _fetch_markets_from_coinpaprika(limit: int) -> List[dict]:
     tickers = await fetch_from_coinpaprika("tickers")
     if not tickers:
@@ -174,6 +215,10 @@ async def fetch_market_movers(limit: int) -> tuple[List[dict], str]:
             logger.warning("CoinCap movers failed, trying CoinPaprika...")
             rows = await _fetch_markets_from_coinpaprika(limit)
             source = "coinpaprika"
+        if not rows:
+            logger.warning("CoinPaprika movers failed, trying Binance...")
+            rows = await _fetch_markets_from_binance(limit)
+            source = "binance"
 
     if not rows:
         raise HTTPException(status_code=503, detail="All market mover providers unavailable")