Fix post-cluster neutral strength ablation

app/services/backtest_service.py

@@ -156,6 +156,28 @@ def _sr_research_variant() -> str:
     return value
 
 
+def _apply_zone_strength_variant(zone_levels: list[Any], sr_variant: str) -> list[Any]:
+    """Apply post-cluster research controls without changing zone geometry."""
+    if sr_variant == "legacy_geometry_neutral":
+        # Neutrality must be enforced after the shared zone cluster: its legacy
+        # sum mode can otherwise turn two 50-strength constituents back into a
+        # 100-strength target and silently invalidate the ablation.
+        for level in zone_levels:
+            level.strength = 50
+    return zone_levels
+
+
+def _apply_zone_strength_variant(zone_levels: list[Any], sr_variant: str) -> list[Any]:
+    """Apply post-cluster research controls without changing zone geometry."""
+    if sr_variant == "legacy_geometry_neutral":
+        # Neutrality must be enforced after the shared zone cluster: its legacy
+        # sum mode can otherwise turn two 50-strength constituents back into a
+        # 100-strength target and silently invalidate the ablation.
+        for level in zone_levels:
+            level.strength = 50
+    return zone_levels
+
+
 def _backtest_entry_bounds() -> tuple[date | None, date | None]:
     """Optional research-only entry bounds used to protect validation data."""
     parsed: list[date | None] = []
@@ -328,6 +350,8 @@ def _window_setups(
             entry,
             strength_mode=zone_strength_mode,
         )
+        zone_levels = _apply_zone_strength_variant(zone_levels, sr_variant)
+        zone_levels = _apply_zone_strength_variant(zone_levels, sr_variant)
         targets = target_generator.generate_targets(direction, entry, stop, zone_levels, atr)
         if not targets:
             fallback_k = _atr_target_fallback_k()