feat(admin): reconciler marks reaped instances deleted

Without this the row stays active forever, the reconciler re-logs the
same miss every fifteen minutes, and the lifecycle sweep keeps emailing
about an instance that no longer exists.

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

admin/internal/inject/inject.go

@@ -7,6 +7,7 @@ package inject
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log"
 	"time"
@@ -16,6 +17,7 @@ import (
 	"github.com/mrhid6/vantage/shared/license"
 	sharedmodels "github.com/mrhid6/vantage/shared/models"
 	"go.mongodb.org/mongo-driver/v2/bson"
+	"go.mongodb.org/mongo-driver/v2/mongo"
 )
 
 // ReconcileInterval is how often every cloud instance is compared against what
@@ -103,6 +105,19 @@ func Reconcile(ctx context.Context) (checked, repaired int, err error) {
 		var remote sharedmodels.Instance
 		if err := db.Control("instances").FindOne(ctx,
 			bson.M{"instance_id": inst.InstanceID}).Decode(&remote); err != nil {
+			// The control plane's reaper deletes lapsed Free instances. Record
+			// that here rather than re-logging it every fifteen minutes forever,
+			// and so the lifecycle sweep stops emailing about it.
+			if errors.Is(err, mongo.ErrNoDocuments) {
+				if _, uErr := db.Admin("admin_instances").UpdateOne(ctx,
+					bson.M{"instance_id": inst.InstanceID},
+					bson.M{"$set": bson.M{"status": models.StatusDeleted}}); uErr != nil {
+					log.Printf("reconcile: mark %s deleted: %v", inst.InstanceID, uErr)
+				} else {
+					log.Printf("reconcile: instance %s is gone from the control plane; marked deleted", inst.InstanceID)
+				}
+				continue
+			}
 			log.Printf("reconcile: no control-plane instance %s: %v", inst.InstanceID, err)
 			continue
 		}