malkhut: conditional slippage (Fable)

MALKHUT/malkhut/cwm/core.py

@@ -568,8 +568,20 @@ class MinimalCryptoLOBCWM:
         # ── Fill Quality computation ────────────────────────────────────────
         mid = state.book.mid if state.book.bids and state.book.asks else 0.0
         slippage_bps = 0.0
+        expected_slippage_bps = 0.0
         if new_fill_qty > 0 and mid > 0 and new_fill_price > 0:
             slippage_bps = abs(new_fill_price - mid) / mid * 10_000
+            # Conditional: expected slippage from book depth
+            book_depth = state.book.asks if isinstance(our_action, FulfilmentAction) and our_action.side == Side.BUY else state.book.bids if isinstance(our_action, FulfilmentAction) else ()
+            cumulative_usd = 0.0
+            cumulative_levels = 0
+            for level in (book_depth or ()):
+                cumulative_usd += level.price * level.qty
+                cumulative_levels += 1
+                if cumulative_usd >= new_fill_price * new_fill_qty:
+                    break
+            if cumulative_levels > 0:
+                expected_slippage_bps = cumulative_levels * 0.1
         is_maker_fill = (our_action.order_type and our_action.order_type.value == "LIMIT") or our_action.post_only if isinstance(our_action, FulfilmentAction) else False
         price_improvement_bps = 0.0
         if new_fill_qty > 0 and isinstance(our_action, FulfilmentAction) and our_action.post_only and our_action.side:
@@ -594,7 +606,8 @@ class MinimalCryptoLOBCWM:
         fill_value = 0.0
         if new_fill_qty > 0:
             quality = price_improvement_bps if is_maker_fill else max(0.0, spread_bps - slippage_bps)
-            fill_value = quality - abs(post_fill_adverse) * 0.5
+            slippage_surprise = slippage_bps - expected_slippage_bps
+            fill_value = quality - abs(post_fill_adverse) * 0.5 - max(0.0, slippage_surprise) * 0.3
 
         fq = FillQuality(
             filled=new_fill_qty > 0,
@@ -602,6 +615,7 @@ class MinimalCryptoLOBCWM:
             fill_price=new_fill_price,
             requested_qty=our_action.qty_fraction * state.account.available_balance / max(mid, 1e-12) if isinstance(our_action, FulfilmentAction) and our_action.qty_fraction > 0 and mid > 0 else 0.0,
             slippage_bps=slippage_bps,
+            expected_slippage_bps=expected_slippage_bps,
             price_improvement_bps=price_improvement_bps,
             levels_consumed=0,
             is_maker_fill=is_maker_fill,

MALKHUT/malkhut/cwm/hft_cwm.py

@@ -483,11 +483,28 @@ class HftBacktestCWM:
         mid = prev_book.mid if prev_book.bids and prev_book.asks else 0.0
         spread_bps = prev_book.spread_bps if prev_book.bids and prev_book.asks else 0.0
 
-        # Slippage: how far from mid did we fill?
+        # ── CONDITIONAL SLIPPAGE (not constant) ──────────────────────────
+        # Slippage depends on: order size, book depth, levels consumed
         slippage_bps = 0.0
+        expected_slippage_bps = 0.0
         if filled and mid > 0 and new_fill_price > 0:
+            # Actual slippage: how far from mid did we fill?
             slippage_bps = abs(new_fill_price - mid) / mid * 10_000
 
+            # Expected slippage from book depth model (power-law)
+            # Walk levels until we accumulate fill_qty
+            book_depth = prev_book.asks if action.side == Side.BUY else prev_book.bids
+            cumulative_usd = 0.0
+            cumulative_levels = 0
+            for level in (book_depth or ()):
+                level_usd = level.price * level.qty
+                cumulative_usd += level_usd
+                cumulative_levels += 1
+                if cumulative_usd >= new_fill_price * new_fill_qty:
+                    break
+            if cumulative_levels > 0:
+                expected_slippage_bps = cumulative_levels * 0.1  # ~0.1 bps per level consumed
+
         # Price improvement: how much better than best bid/ask?
         price_improvement_bps = 0.0
         if filled and action.post_only and action.side:
@@ -525,11 +542,13 @@ class HftBacktestCWM:
         else:
             rolling_fill_rate = 0.0
 
-        # Composite fill value score
+        # Composite fill value score — conditioned on expected slippage
         fill_value = 0.0
         if filled:
             quality = price_improvement_bps if is_maker else max(0.0, spread_bps - slippage_bps)
-            fill_value = quality - abs(post_fill_adverse) * 0.5
+            # Adjust by slippage surprise: actual vs expected
+            slippage_surprise = slippage_bps - expected_slippage_bps  # positive = worse than expected
+            fill_value = quality - abs(post_fill_adverse) * 0.5 - max(0.0, slippage_surprise) * 0.3
 
         return FillQuality(
             filled=filled,
@@ -537,6 +556,7 @@ class HftBacktestCWM:
             fill_price=new_fill_price,
             requested_qty=action.qty_fraction * prev_state.account.available_balance / max(mid, 1e-12) if action.qty_fraction > 0 and mid > 0 else 0.0,
             slippage_bps=slippage_bps,
+            expected_slippage_bps=expected_slippage_bps,
             price_improvement_bps=price_improvement_bps,
             levels_consumed=levels_consumed,
             is_maker_fill=is_maker,

MALKHUT/malkhut/state.py

@@ -283,6 +283,9 @@ class FillQuality:
     # How close to mid did we fill? (for aggressive: positive = slipped)
     slippage_bps: float = 0.0
 
+    # Expected slippage from book depth model (conditional on actual book state)
+    expected_slippage_bps: float = 0.0
+
     # For passive fills: how much better than best bid/ask? (positive = improvement)
     price_improvement_bps: float = 0.0