feat: add priority demotion controls

apps/api/internal/runner/runtime_policy.go

@@ -73,17 +73,26 @@ func (s *Service) applyPriorityDemotePolicy(ctx context.Context, taskID string,
 	if !decision.Demote {
 		return
 	}
-	if err := s.store.DemoteCandidatePlatformPriority(ctx, candidate.PlatformID, decision.Step); err == nil {
-		s.recordAttemptTrace(ctx, taskID, attemptNo, priorityDemoteTraceEntry(decision, candidate.PlatformID, candidate.PlatformModelID))
+	if dynamicPriority, err := s.store.DemoteCandidatePlatformPriority(ctx, candidate.PlatformID); err == nil {
+		s.recordAttemptTrace(ctx, taskID, attemptNo, priorityDemoteTraceEntry(decision, candidate.PlatformID, candidate.PlatformModelID, dynamicPriority))
 		_ = s.emit(ctx, taskID, "task.policy.priority_demoted", "running", "priority_demote", 0.52, "candidate platform priority demoted by runner policy", addPolicyTracePayload(map[string]any{
 			"platformId":      candidate.PlatformID,
 			"platformModelId": candidate.PlatformModelID,
-			"demoteStep":      decision.Step,
+			"dynamicPriority": dynamicPriority,
 			"code":            clients.ErrorCode(cause),
+			"reason":          decision.Reason,
+			"errorMessage":    messageFromError(cause),
 		}, decision.Match, decision.Info), simulated)
 	}
 }
 
+func messageFromError(err error) string {
+	if err == nil {
+		return ""
+	}
+	return err.Error()
+}
+
 func effectiveRuntimePolicy(base map[string]any, override map[string]any, key string) map[string]any {
 	policy := base
 	if nested, ok := override[key].(map[string]any); ok && len(nested) > 0 {