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_strategy_roll_lib.py

@@ -0,0 +1,59 @@
+from strategy_roll_lib import (
+    preview_roll,
+    resolve_roll_stop_spec,
+    roll_stop_after_fill,
+    unified_stop_from_avg,
+)
+
+
+def test_resolve_roll_stop_spec_treats_small_value_as_offset_pct():
+    mode, val = resolve_roll_stop_spec(new_stop_loss=1.0, entry_ref=63.976)
+    assert mode == "offset"
+    assert val == 1.0
+
+
+def test_resolve_roll_stop_spec_treats_price_as_absolute():
+    mode, val = resolve_roll_stop_spec(new_stop_loss=64.6, entry_ref=63.976)
+    assert mode == "absolute"
+    assert val == 64.6
+
+
+def test_unified_stop_from_avg_short_one_percent():
+    sl = unified_stop_from_avg("short", 63.976, 1.0)
+    assert abs(sl - 63.976 * 1.01) < 1e-6
+
+
+def test_preview_roll_offset_mode_not_breakeven():
+    preview, err = preview_roll(
+        direction="short",
+        symbol="HYPE/USDT",
+        qty_existing=3.0,
+        entry_existing=65.0,
+        initial_take_profit=60.0,
+        add_mode="market",
+        stop_offset_pct=1.0,
+        risk_percent=2.0,
+        capital_base_usdt=1000.0,
+        add_price=64.0,
+        legs_done=1,
+    )
+    assert err is None
+    assert preview["stop_mode"] == "offset"
+    assert preview["stop_offset_pct"] == 1.0
+    avg = preview["avg_entry_after"]
+    sl = preview["new_stop_loss"]
+    assert sl > avg * 1.009
+    assert sl < avg * 1.011
+
+
+def test_roll_stop_after_fill_recomputes_from_actual_fill():
+    sl = roll_stop_after_fill(
+        "short",
+        qty_before=3.0,
+        entry_before=65.0,
+        add_qty=5.0,
+        fill_price=63.5,
+        stop_offset_pct=1.0,
+    )
+    avg = (3 * 65.0 + 5 * 63.5) / 8.0
+    assert abs(sl - avg * 1.01) < 1e-6