Fix Gate/Binance memory regression and roll stop offset from avg.

Stop fetch_tickers fallback for volume rank and keep stale cache on failed refresh. Compute roll unified stop as merge-average plus offset percent instead of break-even.

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

tests/test_hub_volume_rank_lib.py

@@ -84,6 +84,15 @@ def test_scores_from_binance_uses_fapi_lightweight_api():
     ex.fetch_tickers.assert_not_called()
 
 
+def test_scores_from_binance_skips_fetch_tickers_on_api_error():
+    ex = MagicMock()
+    ex.id = "binance"
+    ex.fapiPublicGetTicker24hr.side_effect = RuntimeError("network")
+    scored = _scores_from_binance(ex)
+    assert scored == []
+    ex.fetch_tickers.assert_not_called()
+
+
 def test_scores_from_gate_uses_futures_tickers_api():
     ex = MagicMock()
     ex.id = "gateio"
@@ -96,6 +105,15 @@ def test_scores_from_gate_uses_futures_tickers_api():
     ex.fetch_tickers.assert_not_called()
 
 
+def test_scores_from_gate_skips_fetch_tickers_on_api_error():
+    ex = MagicMock()
+    ex.id = "gateio"
+    ex.publicFuturesGetSettleTickers.side_effect = RuntimeError("network")
+    scored = _scores_from_gate(ex)
+    assert scored == []
+    ex.fetch_tickers.assert_not_called()
+
+
 def test_resolve_daily_volume_rank_caches_result():
     cache = {"version": 0, "updated_at": 0.0, "ranks": {}, "total": 0}
     ex = MagicMock()
@@ -130,6 +148,31 @@ def test_resolve_daily_volume_rank_caches_result():
     assert ex.fapiPublicGetTicker24hr.call_count == calls
 
 
+def test_resolve_daily_volume_rank_keeps_stale_cache_when_refresh_empty():
+    cache = {
+        "version": LIQUIDITY_RANK_CACHE_VERSION,
+        "updated_at": 900.0,
+        "ranks": {"BTC": 1},
+        "total": 100,
+    }
+    ex = MagicMock()
+    ex.id = "binance"
+    ex.fapiPublicGetTicker24hr.return_value = []
+
+    rank, total = resolve_daily_volume_rank(
+        "BTC",
+        cache,
+        now_ts=2000.0,
+        ttl_sec=60.0,
+        exchange=ex,
+        ensure_markets_loaded=lambda: None,
+    )
+    assert rank == 1
+    assert total == 100
+    assert cache["updated_at"] == 900.0
+    ex.fetch_tickers.assert_not_called()
+
+
 def test_build_usdt_swap_volume_ranks():
     ex = MagicMock()
     ex.id = "binance"