Implement AI orchestration wedding demo

backend/app/validation/policy_engine.py

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+from app.config import get_settings
+from app.domain.schemas import PlannerDecision, PolicyResult
+
+
+class PolicyEngine:
+    def __init__(self, existing_payloads: list[dict] | None = None) -> None:
+        self.threshold = get_settings().planner_confidence_threshold
+        self.existing_payloads = existing_payloads or []
+
+    def evaluate(self, decision: PlannerDecision) -> PolicyResult:
+        reasons: list[str] = []
+        if decision.confidence < self.threshold:
+            reasons.append(f"Confidence {decision.confidence:.2f} is below threshold {self.threshold:.2f}.")
+        if decision.arguments in self.existing_payloads:
+            reasons.append("Duplicate pending action payload.")
+        if decision.tool == "create_guest_reservation" and not decision.arguments.get("event_date"):
+            reasons.append("Reservation requires a date.")
+        if decision.tool == "create_guest_reservation" and not decision.arguments.get("partner_id"):
+            reasons.append("Reservation requires a Wed partner_id.")
+        if decision.tool == "create_task" and not decision.arguments.get("title"):
+            reasons.append("Task requires a title.")
+        return PolicyResult(allowed=not reasons, reasons=reasons)