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

internal/quitcheckin/handler/supervisor_handler.go

@@ -62,6 +62,8 @@ func (h *Handler) BindSupervisorInvite(c *gin.Context) {
 				msg = "不能绑定自己"
 			case "监督关系已存在":
 				msg = "已绑定，无需重复操作"
+			case "监督人已达上限":
+				msg = "对方监督人已达上限（最多 3 人）"
 			}
 		}
 		c.JSON(http.StatusBadRequest, model.Error(http.StatusBadRequest, msg))

internal/quitcheckin/service/supervisor.go

@@ -40,14 +40,17 @@ type SupervisorStatusResult struct {
 }
 
 var (
-	ErrInviteNotFound  = errors.New("邀请不存在")
-	ErrInviteExpired   = errors.New("邀请已过期")
-	ErrInviteUsed      = errors.New("邀请已被使用")
-	ErrCannotBindSelf  = errors.New("不能绑定自己为监督人")
-	ErrBindingExists   = errors.New("监督关系已存在")
-	ErrBindingNotFound = errors.New("监督关系不存在")
+	ErrInviteNotFound         = errors.New("邀请不存在")
+	ErrInviteExpired          = errors.New("邀请已过期")
+	ErrInviteUsed             = errors.New("邀请已被使用")
+	ErrCannotBindSelf         = errors.New("不能绑定自己为监督人")
+	ErrBindingExists          = errors.New("监督关系已存在")
+	ErrBindingNotFound        = errors.New("监督关系不存在")
+	ErrSupervisorLimitReached = errors.New("监督人已达上限")
 )
 
+const maxSupervisorsPerOwner = 3
+
 func (s *Service) CreateSupervisorInvite(ctx context.Context, ownerUID int, now time.Time, days int) (SupervisorInviteResult, error) {
 	if days <= 0 {
 		days = 7
@@ -113,6 +116,18 @@ func (s *Service) BindSupervisorInvite(ctx context.Context, supervisorUID int, t
 			return err
 		}
 
+		// 多人监督：允许多个 supervisor，但限制最多 3 个 active supervisor。
+		var activeCount int64
+		if err := tx.WithContext(ctx).
+			Model(&quitmodel.SupervisorBinding{}).
+			Where("owner_uid = ? AND status = ?", invite.OwnerUID, "active").
+			Count(&activeCount).Error; err != nil {
+			return err
+		}
+		if activeCount >= maxSupervisorsPerOwner {
+			return ErrSupervisorLimitReached
+		}
+
 		binding := quitmodel.SupervisorBinding{
 			OwnerUID:      invite.OwnerUID,
 			SupervisorUID: supervisorUID,

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)
+	}
+}