feat: planner config (weights, thresholds, K) and shared types

backend/app/services/planner/config.py

@@ -0,0 +1,42 @@
+"""Planner constants. Tune here without touching algorithm code."""
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class PlannerConfig:
+    # Hard constraints
+    recency_weeks: int = 4              # constraint #3: no repeat within N weeks
+    calorie_tolerance_pct: int = 20     # constraint #4: ±X% of family.calorie_target
+    max_total_minutes: int = 45         # constraint #5: prep + cook
+    max_meal_cost: float = 30.00        # constraint #6: dollars per meal
+
+    # Scoring weights (must sum to 1.0)
+    w_savings: float = 0.30
+    w_coverage: float = 0.25
+    w_pantry: float = 0.10
+    w_time: float = 0.15
+    w_recency: float = 0.20
+
+    # Time bonus boundaries
+    time_ideal_minutes: int = 25        # full bonus at <= this
+    time_full_minutes: int = 45         # zero bonus at this; matches max_total_minutes
+
+    # Recency bonus boundary
+    recency_full_weeks: int = 12        # full bonus when last cooked >= this many weeks ago
+
+    # Set selection
+    top_k: int = 20                     # how many feasible recipes to enumerate over
+    set_size: int = 3                   # 3 dinners/week
+    p_protein: float = 0.15             # diversity penalty per shared-protein pair
+    p_cuisine: float = 0.10             # diversity penalty per shared-cuisine pair
+
+    def validate(self) -> None:
+        total = self.w_savings + self.w_coverage + self.w_pantry + self.w_time + self.w_recency
+        if abs(total - 1.0) > 1e-6:
+            raise ValueError(f"weights must sum to 1.0, got {total}")
+
+
+DEFAULT = PlannerConfig()
+DEFAULT.validate()