feat(supervisor): allow up to 3 supervisors per owner

internal/quitcheckin/service/supervisor_test.go

@@ -2,6 +2,7 @@ package service
 
 import (
 	"context"
+	"errors"
 	"testing"
 	"time"
 
@@ -51,7 +52,6 @@ func TestSupervisorInviteBindAndOverview(t *testing.T) {
 	supervisorUID := 3002
 	now := time.Date(2026, 4, 16, 10, 0, 0, 0, time.Local)
 
-	// seed users
 	if err := db.Create(&usermodel.User{ID: uint(ownerUID), NickName: "owner"}).Error; err != nil {
 		t.Fatalf("seed owner user: %v", err)
 	}
@@ -150,3 +150,55 @@ func TestSupervisorRevokeBindingBySupervisor(t *testing.T) {
 		t.Fatalf("overview items=%d, want=0 after revoke", len(overview.Items))
 	}
 }
+
+func TestSupervisorBindRespectsMaxSupervisors(t *testing.T) {
+	t.Parallel()
+
+	db := setupSupervisorTestDB(t)
+	svc := NewService(db)
+	ctx := context.Background()
+
+	ownerUID := 3201
+	now := time.Date(2026, 4, 16, 10, 0, 0, 0, time.Local)
+
+	if err := db.Create(&usermodel.User{ID: uint(ownerUID), NickName: "owner"}).Error; err != nil {
+		t.Fatalf("seed owner user: %v", err)
+	}
+
+	startDate := time.Date(2026, 4, 10, 0, 0, 0, 0, time.Local)
+	if _, err := svc.UpsertProfile(ctx, ownerUID, UpsertProfileRequest{
+		QuitStartDate:      &startDate,
+		PackPriceCent:      intPtr(2500),
+		BaselineCigsPerDay: intPtr(10),
+	}, "owner", "", now); err != nil {
+		t.Fatalf("upsert profile: %v", err)
+	}
+
+	for i := 0; i < 3; i++ {
+		supervisorUID := 3300 + i
+		if err := db.Create(&usermodel.User{ID: uint(supervisorUID), NickName: "s"}).Error; err != nil {
+			t.Fatalf("seed supervisor user: %v", err)
+		}
+		invite, err := svc.CreateSupervisorInvite(ctx, ownerUID, now, 7)
+		if err != nil {
+			t.Fatalf("create invite: %v", err)
+		}
+		if err := svc.BindSupervisorInvite(ctx, supervisorUID, invite.Token, now); err != nil {
+			t.Fatalf("bind #%d: %v", i+1, err)
+		}
+	}
+
+	supervisorUID := 3399
+	if err := db.Create(&usermodel.User{ID: uint(supervisorUID), NickName: "s4"}).Error; err != nil {
+		t.Fatalf("seed supervisor user: %v", err)
+	}
+	invite, err := svc.CreateSupervisorInvite(ctx, ownerUID, now, 7)
+	if err != nil {
+		t.Fatalf("create invite: %v", err)
+	}
+	if err := svc.BindSupervisorInvite(ctx, supervisorUID, invite.Token, now); err == nil {
+		t.Fatalf("bind #4 should fail")
+	} else if !errors.Is(err, ErrSupervisorLimitReached) {
+		t.Fatalf("bind #4 err=%v, want ErrSupervisorLimitReached", err)
+	}
+}