fix: reorder HeuristicRouter rules so low-complexity check precedes math check (#671)

* fix: reorder HeuristicRouter rules so low-complexity check precedes math check

Trivial arithmetic like "what is 2+2?" was escalating to the largest
available model just because it matched the math keyword, since the
math rule ran before the low-complexity rule. Math queries above the
low-complexity threshold still escalate correctly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix: make low-complexity math routing effective

---------

Co-authored-by: Ari <ari.silva@paipe.co>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
Co-authored-by: Elliot Slusky <elliot@slusky.com>

src/openjarvis/learning/routing/router.py

@@ -93,11 +93,16 @@ class HeuristicRouter(RouterPolicy):
 
     Rules (applied in order):
     1. Code detected → prefer model with "code"/"coder" in name
-    2. Math detected → prefer larger model
-    3. Low complexity (score < 0.20) → prefer smaller/faster model
+    2. Low complexity (score <= 0.20) → prefer smaller/faster model
+    3. Math detected → prefer larger model
     4. High complexity (score >= 0.55 OR reasoning keywords) → prefer larger model
     5. High urgency (>0.8) → override to smaller model
     6. Default fallback → default_model → fallback_model → first available
+
+    Low complexity is checked before the math check so that simple arithmetic
+    ("calculate 2+2") routes to the smallest model instead of always escalating
+    on the "math" keyword; math problems above the low-complexity threshold
+    still escalate to the larger model.
     """
 
     def __init__(
@@ -134,14 +139,15 @@ class HeuristicRouter(RouterPolicy):
             # Fall through to larger model for code
             return _largest_model(available) or available[0]
 
-        # Rule 2: Math detected → prefer larger model
+        # Rule 2: Low complexity → prefer smaller model (checked before the math
+        # rule so simple arithmetic doesn't escalate to the largest model)
+        if context.complexity_score <= 0.20:
+            return _smallest_model(available) or available[0]
+
+        # Rule 3: Math detected → prefer larger model
         if context.has_math:
             return _largest_model(available) or available[0]
 
-        # Rule 3: Low complexity → prefer smaller model
-        if context.complexity_score < 0.20:
-            return _smallest_model(available) or available[0]
-
         # Rule 4: High complexity or reasoning → prefer larger model
         if context.complexity_score >= 0.55 or context.has_reasoning:
             return _largest_model(available) or available[0]

tests/learning/test_router.py

@@ -88,13 +88,25 @@ class TestHeuristicRouter:
         router = HeuristicRouter(
             available_models=["small", "large", "coder"],
         )
-        ctx = RoutingContext(
-            query="solve x",
-            query_length=7,
-            has_math=True,
-        )
+        ctx = build_routing_context("solve the integral of x^2 dx")
+        assert ctx.has_math is True
+        assert ctx.complexity_score > 0.20
         assert router.select_model(ctx) == "large"
 
+    def test_low_complexity_math_prefers_small(self) -> None:
+        """Regression test: a trivial math query ("calculate 2+2") must not
+        escalate to the largest model just because it contains a math
+        keyword — the low-complexity rule takes priority over the math rule.
+        """
+        _register_models()
+        router = HeuristicRouter(
+            available_models=["small", "large", "coder"],
+        )
+        ctx = build_routing_context("calculate 2+2")
+        assert ctx.has_math is True
+        assert ctx.complexity_score == 0.20
+        assert router.select_model(ctx) == "small"
+
     def test_high_complexity_prefers_large(self) -> None:
         _register_models()
         router = HeuristicRouter(

tests/learning/test_routing_models.py

@@ -77,11 +77,9 @@ class TestRouterWithNewModels:
         router = HeuristicRouter(
             available_models=NEW_LOCAL_MODELS,
         )
-        ctx = RoutingContext(
-            query="solve the integral of x^2 dx",
-            query_length=29,
-            has_math=True,
-        )
+        ctx = build_routing_context("solve the integral of x^2 dx")
+        assert ctx.has_math is True
+        assert ctx.complexity_score > 0.20
         selected = router.select_model(ctx)
         assert selected == "gpt-oss:120b"