diff --git a/backend/internal/handler/admin/user_handler.go b/backend/internal/handler/admin/user_handler.go
index 24e4540f36..817bfa9117 100644
--- a/backend/internal/handler/admin/user_handler.go
+++ b/backend/internal/handler/admin/user_handler.go
@@ -790,15 +790,21 @@ func (h *UserHandler) UpdateUserPlatformQuotas(c *gin.Context) {
 		}
 	}
 
+	// 三档全空的输入不落库：user_platform_quotas 只保存至少配置了一档限额的记录，
+	// 不存在的行等价于不限额。未进入 records 的平台由 UpsertForUser 软删，审计里记为 removed。
 	records := make([]service.UserPlatformQuotaRecord, 0, len(req.Quotas))
 	for _, q := range req.Quotas {
-		records = append(records, service.UserPlatformQuotaRecord{
+		rec := service.UserPlatformQuotaRecord{
 			UserID:          userID,
 			Platform:        q.Platform,
 			DailyLimitUSD:   q.DailyLimitUSD,
 			WeeklyLimitUSD:  q.WeeklyLimitUSD,
 			MonthlyLimitUSD: q.MonthlyLimitUSD,
-		})
+		}
+		if !rec.HasAnyLimit() {
+			continue
+		}
+		records = append(records, rec)
 	}
 
 	ctx := c.Request.Context()
@@ -860,6 +866,7 @@ func (h *UserHandler) UpdateUserPlatformQuotas(c *gin.Context) {
 	slog.Info("admin.quota_updated",
 		"actor_admin_id", getAdminIDFromContext(c),
 		"target_user_id", userID,
+		"submitted_count", len(req.Quotas),
 		"platform_count", len(records),
 		"before_snapshot_available", beforeErr == nil,
 		"changes", changes)
diff --git a/backend/internal/handler/admin/user_platform_quota_admin_test.go b/backend/internal/handler/admin/user_platform_quota_admin_test.go
index f1d1b5b605..cf512164e5 100644
--- a/backend/internal/handler/admin/user_platform_quota_admin_test.go
+++ b/backend/internal/handler/admin/user_platform_quota_admin_test.go
@@ -112,16 +112,61 @@ func TestUpdateUserPlatformQuotas_Success(t *testing.T) {
 	if len(repo.upsertCalls) != 1 {
 		t.Fatalf("UpsertForUser should be called once, got %d", len(repo.upsertCalls))
 	}
-	// upsert 记录数 = 请求体中给出的平台数（未给出的平台不落库）。
-	if repo.upsertCalls[0].userID != 42 || len(repo.upsertCalls[0].records) != 5 {
+	// upsert 记录数 = 请求体中至少配置了一档限额的平台数；三档全空的平台不落库，
+	// 由 UpsertForUser 的"不在列表里就软删"分支处理。
+	if repo.upsertCalls[0].userID != 42 || len(repo.upsertCalls[0].records) != 2 {
 		t.Errorf("unexpected upsert call: %+v", repo.upsertCalls[0])
 	}
+	for _, r := range repo.upsertCalls[0].records {
+		if r.Platform != "anthropic" && r.Platform != "openai" {
+			t.Errorf("platform %q has no configured limit and must not be upserted", r.Platform)
+		}
+	}
 	// 缓存失效：按全部允许平台统一失效（含 kimi/zhipu/deepseek）。
 	if len(cache.deleteCalls) != len(service.AllowedQuotaPlatforms) {
 		t.Errorf("expected %d cache delete calls, got %d: %+v", len(service.AllowedQuotaPlatforms), len(cache.deleteCalls), cache.deleteCalls)
 	}
 }
 
+// TestUpdateUserPlatformQuotas_AllUnlimitedClearsRows 锁定：全部平台三档全空等价于清空，
+// UpsertForUser 收到空列表（软删该用户所有活跃行），且 0 = 显式禁用仍算已配置。
+func TestUpdateUserPlatformQuotas_AllUnlimitedClearsRows(t *testing.T) {
+	repo := &upsertCapturingQuotaRepo{}
+	cache := &billingCacheStub{}
+	h := buildTestHandler(repo, cache)
+
+	body := `{"quotas":[
+		{"platform":"anthropic","daily_limit_usd":null,"weekly_limit_usd":null,"monthly_limit_usd":null},
+		{"platform":"openai"}
+	]}`
+	c, w := putReq(t, body)
+	h.UpdateUserPlatformQuotas(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if len(repo.upsertCalls) != 1 {
+		t.Fatalf("UpsertForUser should be called once, got %d", len(repo.upsertCalls))
+	}
+	if len(repo.upsertCalls[0].records) != 0 {
+		t.Errorf("all-unlimited input must upsert zero records, got %+v", repo.upsertCalls[0].records)
+	}
+
+	repo = &upsertCapturingQuotaRepo{}
+	h = buildTestHandler(repo, &billingCacheStub{})
+	c, w = putReq(t, `{"quotas":[{"platform":"gemini","daily_limit_usd":0}]}`)
+	h.UpdateUserPlatformQuotas(c)
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if len(repo.upsertCalls) != 1 || len(repo.upsertCalls[0].records) != 1 {
+		t.Fatalf("zero limit is a configured limit and must be upserted: %+v", repo.upsertCalls)
+	}
+	if r := repo.upsertCalls[0].records[0]; r.Platform != "gemini" || r.DailyLimitUSD == nil || *r.DailyLimitUSD != 0 {
+		t.Errorf("unexpected record: %+v", r)
+	}
+}
+
 func TestUpdateUserPlatformQuotas_RejectsDuplicatePlatform(t *testing.T) {
 	h := buildTestHandler(&upsertCapturingQuotaRepo{}, &billingCacheStub{})
 	body := `{"quotas":[
diff --git a/backend/internal/repository/user_platform_quota_repo.go b/backend/internal/repository/user_platform_quota_repo.go
index ccba2330ce..2e085ba4bc 100644
--- a/backend/internal/repository/user_platform_quota_repo.go
+++ b/backend/internal/repository/user_platform_quota_repo.go
@@ -10,7 +10,6 @@ import (
 	dbent "github.com/Wei-Shaw/sub2api/ent"
 	"github.com/Wei-Shaw/sub2api/ent/userplatformquota"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/timezone"
-	"github.com/lib/pq"
 )
 
 // UserPlatformQuotaRecord 是 repository 层的传输结构体，
@@ -29,10 +28,16 @@ type UserPlatformQuotaRecord struct {
 	MonthlyWindowStart *time.Time
 }
 
+// HasAnyLimit 报告该记录是否至少配置了一档限额（0 也算配置）。
+// 三档全空的记录视为未配置：不写入 user_platform_quotas，等价于不限额。
+func (r UserPlatformQuotaRecord) HasAnyLimit() bool {
+	return r.DailyLimitUSD != nil || r.WeeklyLimitUSD != nil || r.MonthlyLimitUSD != nil
+}
+
 // ErrUserPlatformQuotaNotFound 用于 ResetExpiredWindow 等需要"必须命中已有记录"的方法。
 var ErrUserPlatformQuotaNotFound = fmt.Errorf("user platform quota record not found")
 
-// ErrUserPlatformQuotaFKViolation 当批量 UPSERT 中存在 user_id 不在 users 表的记录时返回。
+// ErrUserPlatformQuotaFKViolation 表示批量快照写入命中了 user_id 不在 users 表的记录。
 var ErrUserPlatformQuotaFKViolation = errors.New("user platform quota snapshot FK violation")
 
 // UserPlatformQuotaSnapshot 是 BatchSnapshotUsage 的输入结构体，
@@ -50,21 +55,20 @@ type UserPlatformQuotaSnapshot struct {
 
 // UserPlatformQuotaRepository 定义用户平台配额的数据访问接口。
 type UserPlatformQuotaRepository interface {
-	// BulkInsertInitial 幂等批量插入初始配额记录（ON CONFLICT DO NOTHING）。
+	// BulkInsertInitial 幂等批量插入初始配额记录：冲突时只补既有行为 NULL 的档位；三档全空的记录跳过。
 	BulkInsertInitial(ctx context.Context, records []UserPlatformQuotaRecord) error
 	// GetByUserPlatform 查询单条配额记录，未找到时返回 (nil, nil)。
 	GetByUserPlatform(ctx context.Context, userID int64, platform string) (*UserPlatformQuotaRecord, error)
 	// ListByUser 查询用户的所有平台配额记录（排除软删除）。
 	ListByUser(ctx context.Context, userID int64) ([]UserPlatformQuotaRecord, error)
-	// IncrementUsageWithReset 原子地累加用量，若窗口已过期则先重置再累加。
+	// IncrementUsageWithReset 原子地累加用量，若窗口已过期则先重置再累加；记录不存在时不建行、直接返回 nil。
 	IncrementUsageWithReset(ctx context.Context, userID int64, platform string, cost float64, now time.Time) error
 	// ResetExpiredWindow 重置指定窗口（daily/weekly/monthly）的用量与起始时间。
 	ResetExpiredWindow(ctx context.Context, userID int64, platform string, window string, newStart time.Time) error
-	// UpsertForUser 全量替换该用户所有平台限额配置（详见 service.UserPlatformQuotaRepository.UpsertForUser）。
+	// UpsertForUser 全量替换该用户所有平台限额配置；三档全空的记录视为未配置（详见实现注释）。
 	UpsertForUser(ctx context.Context, userID int64, records []UserPlatformQuotaRecord) error
-	// BatchSnapshotUsage 用一条多行 UPSERT 把整批 usage 以绝对值覆盖写入(非累加)。
-	// usage/window_start 直接取 EXCLUDED(Redis 当前窗口快照),无 CASE。整批共用 now 作 created/updated_at。
-	// 要求 snapshots 内 (user,platform) 不重复。FK 违反返回 ErrUserPlatformQuotaFKViolation。
+	// BatchSnapshotUsage 把整批 usage 以绝对值覆盖写入既有活跃行(非累加)；行不存在或已软删的 (user,platform) 跳过。
+	// usage/window_start 直接取 Redis 当前窗口快照。整批共用 now 作 updated_at。要求 snapshots 内 (user,platform) 不重复。
 	BatchSnapshotUsage(ctx context.Context, snapshots []UserPlatformQuotaSnapshot, now time.Time) error
 }
 
@@ -77,18 +81,17 @@ func NewUserPlatformQuotaRepository(client *dbent.Client) UserPlatformQuotaRepos
 	return &userPlatformQuotaRepository{client: client}
 }
 
-// BulkInsertInitial 用原生 SQL ON CONFLICT 实现幂等批量插入（带条件 limit 覆盖）。
+// BulkInsertInitial 用原生 SQL ON CONFLICT 实现幂等批量插入。
 // 仅插入 limit_usd 与元数据，usage_usd 用 DB 默认 0，window_start 留 NULL。
+// 三档限额全空的记录视为未配置，跳过不插入。
 // FK 约束要求 user_id 在 users 表中存在，调用方负责保证。
 //
-// 冲突策略：CASE WHEN existing.*_limit_usd IS NULL THEN EXCLUDED.*_limit_usd ELSE existing ...
-//   - 若 IncrementUsageWithReset 因时序问题已先建行（limit 全 NULL），
-//     此处会把注册时的默认 limit 写入，避免该用户在该平台永久无限额。
-//   - 若管理员已通过 UpsertForUser 设置了非 NULL 个性化 limit，**保留不动**
-//     —— 旧实现无条件 EXCLUDED 覆盖会丢失个性化配置。
+// 冲突策略：COALESCE(existing.*_limit_usd, EXCLUDED.*_limit_usd)
+//   - 既有行某档 limit 为 NULL 时写入本次的值，非 NULL 的既有 limit 保持不动。
 //   - 不会改 usage_usd / window_start，保留累计的用量。
 //   - 仅命中 deleted_at IS NULL 的活跃记录（partial unique index 作用域）。
 func (r *userPlatformQuotaRepository) BulkInsertInitial(ctx context.Context, records []UserPlatformQuotaRecord) error {
+	records = configuredRecords(records)
 	if len(records) == 0 {
 		return nil
 	}
@@ -116,8 +119,6 @@ func (r *userPlatformQuotaRepository) BulkInsertInitial(ctx context.Context, rec
 	}
 	// 精确命中 partial unique index（deleted_at IS NULL），避免对软删记录的歧义冲突。
 	// 条件覆盖：仅在现有 limit 为 NULL 时才写入 EXCLUDED，否则保留现有非 NULL 值。
-	// - 修复 IncrementUsageWithReset 已用 NULL limit 建行的场景（NULL → 注册默认）
-	// - 保护管理员通过 UpsertForUser 设置的个性化 limit 不被静默覆盖
 	_, _ = sb.WriteString(` ON CONFLICT (user_id, platform) WHERE deleted_at IS NULL
 		DO UPDATE SET
 			daily_limit_usd   = COALESCE(user_platform_quotas.daily_limit_usd, EXCLUDED.daily_limit_usd),
@@ -169,13 +170,10 @@ func (r *userPlatformQuotaRepository) ListByUser(ctx context.Context, userID int
 
 // IncrementUsageWithReset 原子累加 cost 到 (user, platform) 三个窗口的 *_usage_usd。
 // 行为：
-//   - 若记录存在：在事务内 SELECT FOR UPDATE，按 (prev_window_start vs current_window_start)
+//   - 记录存在：在事务内 SELECT FOR UPDATE，按 (prev_window_start vs current_window_start)
 //     判断是否需要重置（不同 = 重置为 cost；相同 = 累加 cost）
-//   - 若记录不存在（fail-open create 分支）：插入新记录，**limit 字段保留 nil（无限制）**
-//     —— 这是预期行为：billing 链路不能因 quota 表缺失而阻断请求，未注册路径
-//     的用户 quota 默认放行，由调度层指标观测 + 后台对账补建 limit
-//
-// 上层正常路径（注册时 BulkInsertInitial）保证 limit 在记录创建时就被写入。
+//   - 记录不存在：直接返回 nil，不建行。限额只存在于 user_platform_quotas 的行中，
+//     不存在的行等价于不限额，没有可累加的对象。
 func (r *userPlatformQuotaRepository) IncrementUsageWithReset(ctx context.Context, userID int64, platform string, cost float64, now time.Time) error {
 	return r.withTx(ctx, func(txCtx context.Context, txClient *dbent.Client) error {
 		existing, err := txClient.UserPlatformQuota.Query().
@@ -187,25 +185,7 @@ func (r *userPlatformQuotaRepository) IncrementUsageWithReset(ctx context.Contex
 			ForUpdate().
 			Only(txCtx)
 		if dbent.IsNotFound(err) {
-			// fail-open 建行：limit_* 保留 NULL（无限额）。
-			// 用 ON CONFLICT DO UPDATE 累加，而非裸 INSERT：并发下另一请求可能在本事务
-			// SELECT FOR UPDATE 之后、INSERT 之前刚建行，裸 INSERT 会撞 partial unique index
-			// 致事务回滚、本次 cost 丢失；DO UPDATE 把 cost 累加到既有 usage 上。
-			// 写法与本文件 insertLimitsRow / BulkInsertInitial 的 ON CONFLICT 一致。
-			const insertSQL = `INSERT INTO user_platform_quotas
-				(user_id, platform, daily_usage_usd, weekly_usage_usd, monthly_usage_usd,
-				 daily_window_start, weekly_window_start, monthly_window_start, created_at, updated_at)
-				VALUES ($1, $2, $3, $3, $3, $4, $5, $6, $7, $7)
-				ON CONFLICT (user_id, platform) WHERE deleted_at IS NULL DO UPDATE SET
-					daily_usage_usd   = user_platform_quotas.daily_usage_usd   + EXCLUDED.daily_usage_usd,
-					weekly_usage_usd  = user_platform_quotas.weekly_usage_usd  + EXCLUDED.weekly_usage_usd,
-					monthly_usage_usd = user_platform_quotas.monthly_usage_usd + EXCLUDED.monthly_usage_usd,
-					updated_at        = EXCLUDED.updated_at`
-			// $6 = now：30 天滚动月度窗口以当前时刻为起始
-			_, e := txClient.ExecContext(txCtx, insertSQL,
-				userID, platform, cost,
-				timezone.StartOfDay(now), timezone.StartOfWeek(now), now, now)
-			return e
+			return nil
 		}
 		if err != nil {
 			return err
@@ -331,12 +311,13 @@ func monthlyMaybeReset(prevUsage float64, prevStart *time.Time, cost float64, no
 }
 
 // UpsertForUser 全量替换该用户的所有平台限额（事务内）：
-//  1. 软删除未在 records 中出现的所有 active 行
-//  2. 对每条 record 尝试 UPDATE（含 deleted_at = NULL 兼容重激活）；
-//     UPDATE 行数为 0 时 INSERT 新行
+//  1. 软删除未在 records 中出现、或在 records 中但三档全空的所有 active 行
+//  2. 对每条至少配置了一档限额的 record 尝试 UPDATE active 行；UPDATE 行数为 0 时 INSERT 新行
 //
-// 仅改 *_limit_usd + deleted_at + updated_at，保留 *_usage_usd / *_window_start。
+// 仅改 *_limit_usd + updated_at，保留 *_usage_usd / *_window_start。
+// 清空某平台的限额即软删该行并放弃其累计用量；之后再次配置限额会新建行、从新窗口起算。
 func (r *userPlatformQuotaRepository) UpsertForUser(ctx context.Context, userID int64, records []UserPlatformQuotaRecord) error {
+	records = configuredRecords(records)
 	return r.withTx(ctx, func(txCtx context.Context, txClient *dbent.Client) error {
 		platforms := make([]string, 0, len(records))
 		for _, rec := range records {
@@ -391,13 +372,12 @@ func softDeleteMissingPlatforms(ctx context.Context, client *dbent.Client, userI
 }
 
 // updateLimitsRow 尝试 UPDATE active 行（deleted_at IS NULL），返回受影响行数。
-// 仅更新 active 行：若存在多条历史软删记录，加 deleted_at IS NULL 守卫可避免
-// 批量重激活导致的 partial unique index（userplatformquota_user_id_platform_uq）冲突。
-// affected=0 时由调用方 UpsertForUser 走 insertLimitsRow 路径创建新行。
+// 软删行不会被命中：历史软删记录可能有多条，重激活会撞 partial unique index
+// （userplatformquota_user_id_platform_uq）。affected=0 时由调用方 UpsertForUser 走
+// insertLimitsRow 路径创建新行。
 func updateLimitsRow(ctx context.Context, client *dbent.Client, userID int64, rec UserPlatformQuotaRecord, now time.Time) (int64, error) {
 	const query = `UPDATE user_platform_quotas
-		SET daily_limit_usd = $1, weekly_limit_usd = $2, monthly_limit_usd = $3,
-		    deleted_at = NULL, updated_at = $4
+		SET daily_limit_usd = $1, weekly_limit_usd = $2, monthly_limit_usd = $3, updated_at = $4
 		WHERE user_id = $5 AND platform = $6 AND deleted_at IS NULL`
 	res, err := client.ExecContext(ctx, query,
 		rec.DailyLimitUSD, rec.WeeklyLimitUSD, rec.MonthlyLimitUSD, now,
@@ -437,14 +417,14 @@ func insertLimitsRow(ctx context.Context, client *dbent.Client, userID int64, re
 	return nil
 }
 
-// batchRows 是 BatchSnapshotUsage 每批最大行数（9 参/行 × 6000 ≈ 54000 参,低于 Postgres 65535 上限）。
+// batchRows 是 BatchSnapshotUsage 每批最大行数（8 参/行 × 6000 + 1 ≈ 48001 参,低于 Postgres 65535 上限）。
 const batchRows = 6000
 
-// BatchSnapshotUsage 用一条多行 UPSERT 把整批 usage 以绝对值覆盖写入（非累加）。
+// BatchSnapshotUsage 用一条多行 UPDATE ... FROM (VALUES ...) 把整批 usage 以绝对值覆盖写入既有活跃行（非累加）。
 // 每批最多 batchRows 行；$1=now 共用；每行 8 个 per-row 参（user_id, platform, 3×usage, 3×window_start）。
-// FK 违反（user_id 不存在）返回 ErrUserPlatformQuotaFKViolation。
+// 只命中 deleted_at IS NULL 的既有行：行不存在或已软删的 (user, platform) 直接跳过，不建行。
 //
-// 注意:snapshots 超过 batchRows 会分多条 SQL 执行且【非单事务】——若某子批 FK 失败,
+// 注意:snapshots 超过 batchRows 会分多条 SQL 执行且【非单事务】——若某子批失败,
 // 先前子批已写入无法回滚。调用方(flusher)应保证单次 batchSize ≤ batchRows
 // (默认 flush_batch_size=1000 < 6000,安全)。
 // 另注:启用 flusher 后,本绝对值覆盖与 admin 直写 DB(ResetExpiredWindow/UpsertForUser)存在覆盖竞态,
@@ -465,19 +445,25 @@ func (r *userPlatformQuotaRepository) BatchSnapshotUsage(ctx context.Context, sn
 
 		var sb strings.Builder
 		_, _ = sb.WriteString(
-			"INSERT INTO user_platform_quotas" +
-				" (user_id, platform, daily_usage_usd, weekly_usage_usd, monthly_usage_usd," +
-				" daily_window_start, weekly_window_start, monthly_window_start, created_at, updated_at)" +
-				" VALUES ")
+			"UPDATE user_platform_quotas AS q SET" +
+				"  daily_usage_usd      = v.daily_usage_usd," +
+				"  weekly_usage_usd     = v.weekly_usage_usd," +
+				"  monthly_usage_usd    = v.monthly_usage_usd," +
+				"  daily_window_start   = v.daily_window_start," +
+				"  weekly_window_start  = v.weekly_window_start," +
+				"  monthly_window_start = v.monthly_window_start," +
+				"  updated_at           = $1" +
+				" FROM (VALUES ")
 
 		// $1 = now（共用）；每行 8 个 per-row 参，从 $2 起连续编号。
+		// VALUES 里的占位符显式转型，避免 Postgres 对多行 VALUES 推断不出参数类型。
 		args := []any{now}
 		for i, s := range batch {
 			if i > 0 {
 				_, _ = sb.WriteString(",")
 			}
 			b := len(args) // 当前 per-row 第一个参数的 0-based 索引，实际占位符 = b+1
-			fmt.Fprintf(&sb, "($%d,$%d,$%d,$%d,$%d,$%d,$%d,$%d,$1,$1)",
+			fmt.Fprintf(&sb, "($%d::bigint,$%d::varchar,$%d::numeric,$%d::numeric,$%d::numeric,$%d::timestamptz,$%d::timestamptz,$%d::timestamptz)",
 				b+1, b+2, b+3, b+4, b+5, b+6, b+7, b+8)
 			args = append(args,
 				s.UserID, s.Platform,
@@ -487,22 +473,24 @@ func (r *userPlatformQuotaRepository) BatchSnapshotUsage(ctx context.Context, sn
 		}
 
 		_, _ = sb.WriteString(
-			" ON CONFLICT (user_id, platform) WHERE deleted_at IS NULL DO UPDATE SET" +
-				"  daily_usage_usd      = EXCLUDED.daily_usage_usd," +
-				"  weekly_usage_usd     = EXCLUDED.weekly_usage_usd," +
-				"  monthly_usage_usd    = EXCLUDED.monthly_usage_usd," +
-				"  daily_window_start   = EXCLUDED.daily_window_start," +
-				"  weekly_window_start  = EXCLUDED.weekly_window_start," +
-				"  monthly_window_start = EXCLUDED.monthly_window_start," +
-				"  updated_at           = EXCLUDED.updated_at")
+			") AS v(user_id, platform, daily_usage_usd, weekly_usage_usd, monthly_usage_usd," +
+				" daily_window_start, weekly_window_start, monthly_window_start)" +
+				" WHERE q.user_id = v.user_id AND q.platform = v.platform AND q.deleted_at IS NULL")
 
 		if _, err := client.ExecContext(ctx, sb.String(), args...); err != nil {
-			var pqErr *pq.Error
-			if errors.As(err, &pqErr) && pqErr.Code == "23503" {
-				return ErrUserPlatformQuotaFKViolation
-			}
 			return err
 		}
 	}
 	return nil
 }
+
+// configuredRecords 过滤出至少配置了一档限额的记录；三档全空的记录视为未配置。
+func configuredRecords(records []UserPlatformQuotaRecord) []UserPlatformQuotaRecord {
+	out := make([]UserPlatformQuotaRecord, 0, len(records))
+	for _, rec := range records {
+		if rec.HasAnyLimit() {
+			out = append(out, rec)
+		}
+	}
+	return out
+}
diff --git a/backend/internal/repository/user_platform_quota_repo_integration_test.go b/backend/internal/repository/user_platform_quota_repo_integration_test.go
index c9433adc87..6cfe952823 100644
--- a/backend/internal/repository/user_platform_quota_repo_integration_test.go
+++ b/backend/internal/repository/user_platform_quota_repo_integration_test.go
@@ -10,6 +10,8 @@ import (
 	"time"
 
 	dbent "github.com/Wei-Shaw/sub2api/ent"
+	"github.com/Wei-Shaw/sub2api/ent/schema/mixins"
+	"github.com/Wei-Shaw/sub2api/ent/userplatformquota"
 	"github.com/Wei-Shaw/sub2api/internal/service"
 	"github.com/stretchr/testify/require"
 )
@@ -23,6 +25,16 @@ func mustCreateUserForQuota(t *testing.T, client *dbent.Client) int64 {
 	return u.ID
 }
 
+// mustSeedQuotaRow 为 (user, platform) 建一条带 daily limit 的活跃记录。
+// IncrementUsageWithReset 只累加已存在的记录，累加类测试先用它建行。
+func mustSeedQuotaRow(t *testing.T, ctx context.Context, repo UserPlatformQuotaRepository, userID int64, platform string) {
+	t.Helper()
+	limit := 1000.0
+	require.NoError(t, repo.BulkInsertInitial(ctx, []UserPlatformQuotaRecord{
+		{UserID: userID, Platform: platform, DailyLimitUSD: &limit},
+	}))
+}
+
 func TestUserPlatformQuotaRepository_BulkInsertInitial_Idempotent(t *testing.T) {
 	ctx := context.Background()
 	tx := testEntTx(t)
@@ -36,17 +48,17 @@ func TestUserPlatformQuotaRepository_BulkInsertInitial_Idempotent(t *testing.T)
 	daily := 5.0
 	records := []UserPlatformQuotaRecord{
 		{UserID: userID, Platform: "anthropic", DailyLimitUSD: &daily},
-		{UserID: userID, Platform: "openai"},
+		{UserID: userID, Platform: "openai"}, // 三档全空 = 未配置，不建行
 	}
 
 	// 第一次插入
 	require.NoError(t, repo.BulkInsertInitial(txCtx, records), "first insert")
-	// 第二次插入应为 no-op（ON CONFLICT DO NOTHING）
+	// 第二次插入应为 no-op（ON CONFLICT 只补 NULL 档位）
 	require.NoError(t, repo.BulkInsertInitial(txCtx, records), "second insert (idempotent)")
 
 	list, err := repo.ListByUser(txCtx, userID)
 	require.NoError(t, err, "list")
-	require.Len(t, list, 2, "expected 2 records after idempotent insert")
+	require.Len(t, list, 1, "only the configured platform gets a row, and only once")
 
 	// 校验 daily_limit_usd 保留
 	var anthropicRec *UserPlatformQuotaRecord
@@ -114,9 +126,9 @@ func TestUserPlatformQuotaRepository_BulkInsertInitial_CNProvidersAllowed(t *tes
 	daily := 12.0
 	records := []UserPlatformQuotaRecord{
 		{UserID: userID, Platform: "kimi", DailyLimitUSD: &daily},
-		{UserID: userID, Platform: "zhipu"},
-		{UserID: userID, Platform: "deepseek"},
-		{UserID: userID, Platform: "minimax"},
+		{UserID: userID, Platform: "zhipu", DailyLimitUSD: &daily},
+		{UserID: userID, Platform: "deepseek", DailyLimitUSD: &daily},
+		{UserID: userID, Platform: "minimax", DailyLimitUSD: &daily},
 	}
 	require.NoError(t, repo.BulkInsertInitial(txCtx, records),
 		"kimi/zhipu/deepseek/minimax 平台应可写入（CHECK 约束已含国产供应商）")
@@ -168,8 +180,9 @@ func TestUserPlatformQuotaRepository_IncrementUsageWithReset_SameWindow(t *testi
 
 	repo := NewUserPlatformQuotaRepository(client)
 	now := time.Date(2026, 5, 22, 10, 0, 0, 0, time.UTC) // 周五
+	mustSeedQuotaRow(t, ctx, repo, userID, "anthropic")
 
-	// 首次调用：应新建记录
+	// 首次累加：window_start 为 NULL 视为窗口过期，usage 重置为 cost
 	require.NoError(t, repo.IncrementUsageWithReset(ctx, userID, "anthropic", 1.5, now))
 
 	rec, err := repo.GetByUserPlatform(ctx, userID, "anthropic")
@@ -195,6 +208,7 @@ func TestUserPlatformQuotaRepository_IncrementUsageWithReset_DailyReset(t *testi
 	userID := mustCreateUserForQuota(t, client)
 
 	repo := NewUserPlatformQuotaRepository(client)
+	mustSeedQuotaRow(t, ctx, repo, userID, "anthropic")
 
 	day1 := time.Date(2026, 5, 22, 10, 0, 0, 0, time.UTC) // 周五（同一周、同一月）
 	day2 := time.Date(2026, 5, 23, 10, 0, 0, 0, time.UTC) // 周六（同一周、同一月）
@@ -215,6 +229,7 @@ func TestUserPlatformQuotaRepository_IncrementUsageWithReset_WeeklyReset(t *test
 	userID := mustCreateUserForQuota(t, client)
 
 	repo := NewUserPlatformQuotaRepository(client)
+	mustSeedQuotaRow(t, ctx, repo, userID, "openai")
 
 	// 5月22日（周五）和 5月25日（下周一），不同周
 	fri := time.Date(2026, 5, 22, 10, 0, 0, 0, time.UTC)
@@ -230,6 +245,26 @@ func TestUserPlatformQuotaRepository_IncrementUsageWithReset_WeeklyReset(t *test
 	require.InDelta(t, 7.0, rec.MonthlyUsageUSD, 1e-9, "monthly accumulates (same month)")
 }
 
+// TestUserPlatformQuotaRepository_IncrementUsageWithReset_NoRowIsNoop 锁定不变式：
+// 没有配额记录的 (user, platform) 累加时不建行、不报错。
+func TestUserPlatformQuotaRepository_IncrementUsageWithReset_NoRowIsNoop(t *testing.T) {
+	ctx := context.Background()
+	client := testEntClient(t)
+	userID := mustCreateUserForQuota(t, client)
+	repo := NewUserPlatformQuotaRepository(client)
+
+	now := time.Date(2026, 5, 22, 10, 0, 0, 0, time.UTC)
+	require.NoError(t, repo.IncrementUsageWithReset(ctx, userID, "anthropic", 1.5, now))
+
+	rec, err := repo.GetByUserPlatform(ctx, userID, "anthropic")
+	require.NoError(t, err)
+	require.Nil(t, rec, "increment on a missing row must not create one")
+
+	list, err := repo.ListByUser(ctx, userID)
+	require.NoError(t, err)
+	require.Empty(t, list)
+}
+
 func TestUserPlatformQuotaRepository_ResetExpiredWindow(t *testing.T) {
 	ctx := context.Background()
 	tx := testEntTx(t)
@@ -324,10 +359,10 @@ func TestUserPlatformQuotaRepository_ResetExpiredWindow_NotFoundReturnsSentinel(
 		"expected ErrUserPlatformQuotaNotFound, got %v", err)
 }
 
-// TestBatchSnapshotUsage_InsertOverwriteMultiKey 验证 BatchSnapshotUsage 的绝对值覆盖语义：
-//  1. 首批插入 2 条（不同 user），验证 daily 等于首批值；
+// TestBatchSnapshotUsage_OverwriteMultiKey 验证 BatchSnapshotUsage 的绝对值覆盖语义：
+//  1. 首批写入 2 条既有行（不同 user），验证 daily 等于首批值；
 //  2. 对同一 key 传不同值，验证 daily 等于新值（绝对覆盖，非累加）。
-func TestBatchSnapshotUsage_InsertOverwriteMultiKey(t *testing.T) {
+func TestBatchSnapshotUsage_OverwriteMultiKey(t *testing.T) {
 	ctx := context.Background()
 	// BatchSnapshotUsage 不开事务（直接写），使用独立 client 保证跨调用可见性。
 	client := testEntClient(t)
@@ -336,13 +371,15 @@ func TestBatchSnapshotUsage_InsertOverwriteMultiKey(t *testing.T) {
 	userID2 := mustCreateUserForQuota(t, client)
 
 	repo := NewUserPlatformQuotaRepository(client)
+	mustSeedQuotaRow(t, ctx, repo, userID1, "anthropic")
+	mustSeedQuotaRow(t, ctx, repo, userID2, "openai")
 
 	now := time.Date(2026, 5, 29, 12, 0, 0, 0, time.UTC)
 	dailyStart := time.Date(2026, 5, 29, 0, 0, 0, 0, time.UTC)
 	weeklyStart := time.Date(2026, 5, 25, 0, 0, 0, 0, time.UTC) // 当周一
 	monthlyStart := time.Date(2026, 5, 1, 0, 0, 0, 0, time.UTC)
 
-	// ── 第一批：插入 2 行 ──────────────────────────────────────────────────────
+	// ── 第一批：覆盖 2 行 ──────────────────────────────────────────────────────
 	firstBatch := []UserPlatformQuotaSnapshot{
 		{
 			UserID:             userID1,
@@ -421,3 +458,48 @@ func TestBatchSnapshotUsage_InsertOverwriteMultiKey(t *testing.T) {
 	require.InDelta(t, 18.8, rec2After.WeeklyUsageUSD, 1e-9, "user2 weekly must be overwritten to 18.8")
 	require.InDelta(t, 28.8, rec2After.MonthlyUsageUSD, 1e-9, "user2 monthly must be overwritten to 28.8")
 }
+
+// TestBatchSnapshotUsage_NoRowIsNoop 锁定不变式：快照只落到既有活跃行；
+// 行不存在或已软删的 (user, platform) 既不建行也不复活。
+func TestBatchSnapshotUsage_NoRowIsNoop(t *testing.T) {
+	ctx := context.Background()
+	client := testEntClient(t)
+	userID := mustCreateUserForQuota(t, client)
+	repo := NewUserPlatformQuotaRepository(client)
+
+	now := time.Date(2026, 5, 29, 12, 0, 0, 0, time.UTC)
+	snap := func(platform string) UserPlatformQuotaSnapshot {
+		return UserPlatformQuotaSnapshot{
+			UserID:             userID,
+			Platform:           platform,
+			DailyUsageUSD:      1.0,
+			WeeklyUsageUSD:     2.0,
+			MonthlyUsageUSD:    3.0,
+			DailyWindowStart:   time.Date(2026, 5, 29, 0, 0, 0, 0, time.UTC),
+			WeeklyWindowStart:  time.Date(2026, 5, 25, 0, 0, 0, 0, time.UTC),
+			MonthlyWindowStart: time.Date(2026, 5, 1, 0, 0, 0, 0, time.UTC),
+		}
+	}
+
+	// 从未有行
+	require.NoError(t, repo.BatchSnapshotUsage(ctx, []UserPlatformQuotaSnapshot{snap("anthropic")}, now))
+	rec, err := repo.GetByUserPlatform(ctx, userID, "anthropic")
+	require.NoError(t, err)
+	require.Nil(t, rec, "snapshot must not create a row")
+
+	// 有过行但已被软删（管理员清空限额）
+	mustSeedQuotaRow(t, ctx, repo, userID, "openai")
+	require.NoError(t, repo.UpsertForUser(ctx, userID, nil))
+	require.NoError(t, repo.BatchSnapshotUsage(ctx, []UserPlatformQuotaSnapshot{snap("openai")}, now))
+	rec, err = repo.GetByUserPlatform(ctx, userID, "openai")
+	require.NoError(t, err)
+	require.Nil(t, rec, "snapshot must not revive or recreate a soft-deleted row")
+
+	// 软删 mixin 默认隐藏已删行，计数全部行需显式跳过
+	all, err := client.UserPlatformQuota.Query().
+		Where(userplatformquota.UserIDEQ(userID)).
+		All(mixins.SkipSoftDelete(ctx))
+	require.NoError(t, err)
+	require.Len(t, all, 1, "only the soft-deleted openai row may exist")
+	require.NotNil(t, all[0].DeletedAt)
+}
diff --git a/backend/internal/repository/user_platform_quota_upsert_test.go b/backend/internal/repository/user_platform_quota_upsert_test.go
index db8e6f4788..e3bfa42936 100644
--- a/backend/internal/repository/user_platform_quota_upsert_test.go
+++ b/backend/internal/repository/user_platform_quota_upsert_test.go
@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/ent/schema/mixins"
 	"github.com/Wei-Shaw/sub2api/ent/userplatformquota"
 	"github.com/stretchr/testify/require"
 )
@@ -146,3 +147,44 @@ func TestUpsertForUser_EmptyClearsAll(t *testing.T) {
 	require.NoError(t, err)
 	require.Empty(t, got)
 }
+
+// TestUpsertForUser_UnlimitedRecordSoftDeletesAndDiscardsUsage 锁定语义：三档全空的记录视为未配置，
+// 等价于该平台不在列表里 → 软删既有行并放弃其累计用量；之后再配置限额会新建行、从新窗口起算。
+func TestUpsertForUser_UnlimitedRecordSoftDeletesAndDiscardsUsage(t *testing.T) {
+	ctx := context.Background()
+	client := testEntClient(t)
+	userID := mustCreateUserForQuota(t, client)
+	repo := NewUserPlatformQuotaRepository(client)
+
+	d := 10.0
+	require.NoError(t, repo.UpsertForUser(ctx, userID, []UserPlatformQuotaRecord{
+		{UserID: userID, Platform: "anthropic", DailyLimitUSD: &d},
+	}))
+	now := time.Date(2026, 5, 22, 10, 0, 0, 0, time.UTC)
+	require.NoError(t, repo.IncrementUsageWithReset(ctx, userID, "anthropic", 7.5, now))
+
+	// 清空限额：提交三档全空的记录
+	require.NoError(t, repo.UpsertForUser(ctx, userID, []UserPlatformQuotaRecord{
+		{UserID: userID, Platform: "anthropic"},
+	}))
+	gone, err := repo.GetByUserPlatform(ctx, userID, "anthropic")
+	require.NoError(t, err)
+	require.Nil(t, gone, "an unlimited record must soft-delete the row instead of keeping it with NULL limits")
+
+	// 重新配置限额：新行从零起算
+	require.NoError(t, repo.UpsertForUser(ctx, userID, []UserPlatformQuotaRecord{
+		{UserID: userID, Platform: "anthropic", DailyLimitUSD: &d},
+	}))
+	back, err := repo.GetByUserPlatform(ctx, userID, "anthropic")
+	require.NoError(t, err)
+	require.NotNil(t, back)
+	require.InDelta(t, 0, back.DailyUsageUSD, 1e-9, "usage restarts from zero")
+	require.Nil(t, back.DailyWindowStart, "window restarts")
+
+	// 软删 mixin 默认隐藏已删行，计数全部行需显式跳过
+	all, err := client.UserPlatformQuota.Query().
+		Where(userplatformquota.UserIDEQ(userID), userplatformquota.PlatformEQ("anthropic")).
+		All(mixins.SkipSoftDelete(ctx))
+	require.NoError(t, err)
+	require.Len(t, all, 2, "one soft-deleted history row plus one active row")
+}
diff --git a/backend/internal/service/auth_email_oauth_auto_test.go b/backend/internal/service/auth_email_oauth_auto_test.go
index d128e6bbcb..316614f534 100644
--- a/backend/internal/service/auth_email_oauth_auto_test.go
+++ b/backend/internal/service/auth_email_oauth_auto_test.go
@@ -75,6 +75,7 @@ func TestEmailOAuthAuto_SnapshotsPlatformQuotaDefaults(t *testing.T) {
 	require.Len(t, quotaRepo.bulkInsertCalls, 1, "createEmailOAuthUser must snapshot platform quotas via BulkInsertInitial")
 
 	records := quotaRepo.bulkInsertCalls[0]
+	require.Len(t, records, 1, "only platforms with a configured limit get a row")
 	var geminiRecord *UserPlatformQuotaRecord
 	for i := range records {
 		if records[i].Platform == "gemini" {
diff --git a/backend/internal/service/auth_oauth_email_flow_test.go b/backend/internal/service/auth_oauth_email_flow_test.go
index 6e57e95016..e5904caeac 100644
--- a/backend/internal/service/auth_oauth_email_flow_test.go
+++ b/backend/internal/service/auth_oauth_email_flow_test.go
@@ -539,6 +539,7 @@ func TestFinalizeOAuthEmailAccount_SnapshotsPlatformQuotaDefaults(t *testing.T)
 	require.Len(t, quotaRepo.bulkInsertCalls, 1, "snapshotPlatformQuotaDefaults must call BulkInsertInitial once on successful OAuth signup")
 
 	records := quotaRepo.bulkInsertCalls[0]
+	require.Len(t, records, 1, "only platforms with a configured limit get a row")
 	var anthropicRecord *UserPlatformQuotaRecord
 	for i := range records {
 		if records[i].Platform == "anthropic" {
diff --git a/backend/internal/service/auth_service.go b/backend/internal/service/auth_service.go
index f17cfbb4d7..f2a76ccb9d 100644
--- a/backend/internal/service/auth_service.go
+++ b/backend/internal/service/auth_service.go
@@ -1930,7 +1930,7 @@ func resolvedTokenVersion(user *User) int64 {
 	return user.TokenVersion ^ fingerprint
 }
 
-// snapshotPlatformQuotaDefaults 把 plan.PlatformQuotas（platform × 3 window）以
+// snapshotPlatformQuotaDefaults 把 plan.PlatformQuotas 中至少配置了一档限额的平台以
 // BulkInsertInitial 形式写入 user_platform_quotas 表。失败 fail-open（仅 warn log）。
 func (s *AuthService) snapshotPlatformQuotaDefaults(ctx context.Context, userID int64, plan *signupGrantPlan) error {
 	if s.userPlatformQuotaRepo == nil || plan == nil || len(plan.PlatformQuotas) == 0 {
@@ -1941,18 +1941,23 @@ func (s *AuthService) snapshotPlatformQuotaDefaults(ctx context.Context, userID
 	// 整个调用方事务被 Postgres 标记 aborted，把"无关紧要的默认配额快照"放大成
 	// "整笔注册失败"（OAuth pending 路径曾因此 500 → 清 cookie → 404）。
 	ctx = dbent.WithoutTx(ctx)
+	// 仅为至少配置了一档限额的平台建行：user_platform_quotas 中不存在的行等价于不限额，
+	// 三档全空的记录不携带任何可执行的限额。
 	records := make([]UserPlatformQuotaRecord, 0, len(plan.PlatformQuotas))
 	for platform, q := range plan.PlatformQuotas {
-		rec := UserPlatformQuotaRecord{
-			UserID:   userID,
-			Platform: platform,
+		if !q.HasAnyLimit() {
+			continue
 		}
-		if q != nil {
-			rec.DailyLimitUSD = q.DailyLimitUSD
-			rec.WeeklyLimitUSD = q.WeeklyLimitUSD
-			rec.MonthlyLimitUSD = q.MonthlyLimitUSD
-		}
-		records = append(records, rec)
+		records = append(records, UserPlatformQuotaRecord{
+			UserID:          userID,
+			Platform:        platform,
+			DailyLimitUSD:   q.DailyLimitUSD,
+			WeeklyLimitUSD:  q.WeeklyLimitUSD,
+			MonthlyLimitUSD: q.MonthlyLimitUSD,
+		})
+	}
+	if len(records) == 0 {
+		return nil
 	}
 	if err := s.userPlatformQuotaRepo.BulkInsertInitial(ctx, records); err != nil {
 		logger.LegacyPrintf("service.auth", "[Auth] Warning: snapshot platform quota failed user=%d: %v (fail-open)", userID, err)
diff --git a/backend/internal/service/auth_service_platform_quota_test.go b/backend/internal/service/auth_service_platform_quota_test.go
index 31e2b21677..1895e6cb22 100644
--- a/backend/internal/service/auth_service_platform_quota_test.go
+++ b/backend/internal/service/auth_service_platform_quota_test.go
@@ -15,6 +15,7 @@ import (
 type fakeInsertRecorder struct {
 	records []UserPlatformQuotaRecord
 	err     error
+	calls   int             // BulkInsertInitial 被调用的次数
 	lastCtx context.Context // 捕获最后一次 BulkInsertInitial 收到的 ctx（用于断言事务隔离）
 }
 
@@ -23,6 +24,7 @@ func (f *fakeInsertRecorder) GetByUserPlatform(_ context.Context, _ int64, _ str
 }
 
 func (f *fakeInsertRecorder) BulkInsertInitial(ctx context.Context, recs []UserPlatformQuotaRecord) error {
+	f.calls++
 	f.lastCtx = ctx
 	if f.err != nil {
 		return f.err
@@ -51,33 +53,70 @@ func (f *fakeInsertRecorder) BatchSnapshotUsage(_ context.Context, _ []UserPlatf
 	return nil
 }
 
+// TestSnapshotPlatformQuotaDefaults_PassesToRepoBulkInsert 锁定不变式：只有至少配置了一档限额的
+// 平台才建行；三档全空（含 nil 条目）的平台不进入 BulkInsertInitial。
 func TestSnapshotPlatformQuotaDefaults_PassesToRepoBulkInsert(t *testing.T) {
 	fakeRepo := &fakeInsertRecorder{}
 	s := &AuthService{userPlatformQuotaRepo: fakeRepo}
 
 	five := 5.0
+	zero := 0.0
 	plan := &signupGrantPlan{
 		PlatformQuotas: map[string]*DefaultPlatformQuotaSetting{
 			"anthropic":   {DailyLimitUSD: &five},
+			"grok":        {MonthlyLimitUSD: &zero}, // 0 = 显式禁用，属于已配置
 			"openai":      {},
 			"gemini":      {},
-			"antigravity": {},
+			"antigravity": nil,
 		},
 	}
 	if err := s.snapshotPlatformQuotaDefaults(context.Background(), 999, plan); err != nil {
 		t.Fatal(err)
 	}
-	if len(fakeRepo.records) != 4 {
-		t.Errorf("expected 4 records, got %d", len(fakeRepo.records))
+	if len(fakeRepo.records) != 2 {
+		t.Fatalf("expected 2 records (anthropic, grok), got %d: %+v", len(fakeRepo.records), fakeRepo.records)
 	}
-	found := false
+	byPlatform := map[string]UserPlatformQuotaRecord{}
 	for _, r := range fakeRepo.records {
-		if r.UserID == 999 && r.Platform == "anthropic" && r.DailyLimitUSD != nil && *r.DailyLimitUSD == 5 {
-			found = true
+		if r.UserID != 999 {
+			t.Errorf("unexpected user id %d", r.UserID)
+		}
+		byPlatform[r.Platform] = r
+	}
+	if r, ok := byPlatform["anthropic"]; !ok || r.DailyLimitUSD == nil || *r.DailyLimitUSD != 5 {
+		t.Error("anthropic daily = 5 not snapshotted")
+	}
+	if r, ok := byPlatform["grok"]; !ok || r.MonthlyLimitUSD == nil || *r.MonthlyLimitUSD != 0 {
+		t.Error("grok monthly = 0 (explicit disable) must be snapshotted")
+	}
+	for _, p := range []string{"openai", "gemini", "antigravity"} {
+		if _, ok := byPlatform[p]; ok {
+			t.Errorf("platform %q has no configured limit and must not get a row", p)
 		}
 	}
-	if !found {
-		t.Error("anthropic daily = 5 not snapshotted")
+}
+
+// TestSnapshotPlatformQuotaDefaults_AllUnlimitedSkipsInsert 锁定：没有任何平台配置限额时，
+// 不调用 BulkInsertInitial（不产生全空的占位行）。
+func TestSnapshotPlatformQuotaDefaults_AllUnlimitedSkipsInsert(t *testing.T) {
+	fakeRepo := &fakeInsertRecorder{}
+	s := &AuthService{userPlatformQuotaRepo: fakeRepo}
+
+	plan := &signupGrantPlan{
+		PlatformQuotas: map[string]*DefaultPlatformQuotaSetting{
+			"anthropic": {},
+			"openai":    {},
+			"gemini":    nil,
+		},
+	}
+	if err := s.snapshotPlatformQuotaDefaults(context.Background(), 999, plan); err != nil {
+		t.Fatal(err)
+	}
+	if fakeRepo.calls != 0 {
+		t.Fatalf("BulkInsertInitial must not be called when no platform has a configured limit, got %d calls", fakeRepo.calls)
+	}
+	if len(fakeRepo.records) != 0 {
+		t.Errorf("expected no records, got %d", len(fakeRepo.records))
 	}
 }
 
diff --git a/backend/internal/service/auth_service_register_test.go b/backend/internal/service/auth_service_register_test.go
index c29fdac0c3..aa7519f3d1 100644
--- a/backend/internal/service/auth_service_register_test.go
+++ b/backend/internal/service/auth_service_register_test.go
@@ -298,19 +298,29 @@ func TestAuthService_Register_SnapshotsPlatformQuotaDefaults(t *testing.T) {
 	require.Len(t, quotaRepo.bulkInsertCalls, 1)
 
 	records := quotaRepo.bulkInsertCalls[0]
-	var openaiRecord *UserPlatformQuotaRecord
-	for i := range records {
-		if records[i].Platform == "openai" {
-			openaiRecord = &records[i]
-			break
-		}
-	}
-	require.NotNil(t, openaiRecord, "expected openai platform record")
+	require.Len(t, records, 1, "only platforms with a configured limit get a row")
+	openaiRecord := records[0]
+	require.Equal(t, "openai", openaiRecord.Platform)
 	require.Equal(t, int64(77), openaiRecord.UserID)
 	require.NotNil(t, openaiRecord.WeeklyLimitUSD)
 	require.InDelta(t, 12.34, *openaiRecord.WeeklyLimitUSD, 0.0001)
 }
 
+func TestAuthService_Register_NoDefaultQuotasSkipsSnapshot(t *testing.T) {
+	repo := &userRepoStub{nextID: 78}
+	quotaRepo := &userPlatformQuotaRepoStub{}
+
+	service := newAuthService(repo, map[string]string{
+		SettingKeyRegistrationEnabled: "true",
+	}, nil, quotaRepo)
+
+	_, user, err := service.Register(context.Background(), "newuser2@test.com", "password")
+	require.NoError(t, err)
+	require.NotNil(t, user)
+
+	require.Empty(t, quotaRepo.bulkInsertCalls, "no configured default limit must not create quota rows")
+}
+
 func TestAuthService_Register_DoesNotSnapshotOnDisabled(t *testing.T) {
 	repo := &userRepoStub{}
 	quotaRepo := &userPlatformQuotaRepoStub{}
diff --git a/backend/internal/service/billing_cache_service.go b/backend/internal/service/billing_cache_service.go
index b1c6e0933e..6ed70a5ba1 100644
--- a/backend/internal/service/billing_cache_service.go
+++ b/backend/internal/service/billing_cache_service.go
@@ -1139,10 +1139,9 @@ func (s *BillingCacheService) checkUserPlatformQuotaEligibility(
 		// 超时 50ms:覆盖正常路径与可接受抖动;Redis 异常时 hot path 不阻塞超过此值。
 		// 用 context.Background()+短超时,避免请求 ctx 取消导致刷新丢失。
 		// 显式 setCancel()(而非 defer):缩短 context 生命周期,避免 defer 延迟到函数返回。
-		// isSentinel 判定「该 entry 无任何 limit」,涵盖两类,跨窗口命中时都跳过 refresh:
-		//   1) A3 回填的 sentinel(DB 无行,短 TTL):refresh 会把短 TTL 误升级为 86400s,有害;
-		//   2) DB 有行但三 limit 全未配置的用户(TTL 86400s):refresh 纯属无意义(TTL 升级本身无害)。
-		// 两类的 enforcement(下方 limit!=nil 比较)都因 limit 全 nil 永远放行,跳过 refresh 均正确。
+		// isSentinel 判定「该 entry 无任何 limit」(DB 无行时回填的短 TTL sentinel),跨窗口命中时跳过 refresh:
+		// refresh 会把短 TTL 误升级为 86400s;其 enforcement(下方 limit!=nil 比较)因 limit 全 nil 永远放行,
+		// 跳过 refresh 不改变结果。
 		isSentinel := entry.DailyLimitUSD == nil && entry.WeeklyLimitUSD == nil && entry.MonthlyLimitUSD == nil
 		if windowExpired && s.cache != nil && !isSentinel {
 			refreshed := &UserPlatformQuotaCacheEntry{
diff --git a/backend/internal/service/setting_service.go b/backend/internal/service/setting_service.go
index 06a1b19f1a..369d255294 100644
--- a/backend/internal/service/setting_service.go
+++ b/backend/internal/service/setting_service.go
@@ -162,6 +162,11 @@ type DefaultPlatformQuotaSetting struct {
 	MonthlyLimitUSD *float64 `json:"monthly"`
 }
 
+// HasAnyLimit 报告是否至少配置了一档限额（0 也算配置）。nil receiver 视为未配置。
+func (q *DefaultPlatformQuotaSetting) HasAnyLimit() bool {
+	return q != nil && (q.DailyLimitUSD != nil || q.WeeklyLimitUSD != nil || q.MonthlyLimitUSD != nil)
+}
+
 type ProviderDefaultGrantSettings struct {
 	Balance          float64
 	Concurrency      int
diff --git a/backend/internal/service/user_platform_quota_flusher.go b/backend/internal/service/user_platform_quota_flusher.go
index 3ee23d2c93..c26b91bc9c 100644
--- a/backend/internal/service/user_platform_quota_flusher.go
+++ b/backend/internal/service/user_platform_quota_flusher.go
@@ -180,7 +180,8 @@ func (s *UserPlatformQuotaUsageFlusher) flushOneBatch(parentCtx context.Context)
 	// 读到旧 usage 快照(此刻 member 已离开脏集),而 admin 随后写 DB、本行 UPSERT 又在 admin 写之后落库,
 	// 则旧快照会覆盖 admin 刚写入的值;DeleteCache 后 Redis MISS,下次 preflight 从 DB 重载被覆盖的旧值。
 	// 因 member 已被 SPOP,admin 侧 SREM/清脏标记无法拦截本批(故未做)。影响有限,暂列为已知取舍:
-	//   - UpsertForUser 改 limit,而本 UPSERT 不写 limit 列 → limit 配置不受影响;
+	//   - UpsertForUser 改 limit,而本 UPDATE 只写既有活跃行的 usage/window 列 → limit 配置不受影响,
+	//     被软删的行不会被本 UPDATE 复活或重建;
 	//   - ResetExpiredWindow 改 usage,但 preflight windowExpired 会在窗口真正过期时自愈重置,
 	//     仅"强制重置未过期窗口"且与本批精确交错时短暂失效;
 	//   - 低频 admin 操作 + 默认 flusher_enabled=false。彻底消除需 version OCC(DB 加 version 列条件 UPSERT),
@@ -193,11 +194,9 @@ func (s *UserPlatformQuotaUsageFlusher) flushOneBatch(parentCtx context.Context)
 
 	if writeErr != nil {
 		if errors.Is(writeErr, ErrUserPlatformQuotaFKViolation) {
-			// 注意:PG FK violation 是整条 INSERT 回滚 → 整批(含同批正常用户)均未写入 DB,
-			// 且这些 key 已被 SPOP 出脏集、此处不 Readd。活跃 key 会在下次请求重新 SADD,
-			// flusher 读 Redis 当前累计绝对值刷库即自愈;低活跃 key 这轮 DB usage 偏低
-			// (Redis 仍是 enforcement 权威,不受影响;DB 仅展示)。已删用户边角的接受取舍,不做逐行重试。
-			// FK 违反：用户已被删除，直接丢弃不 Readd
+			// FK 违反表示对应用户已不存在,快照无处可落:整批丢弃、不 Readd。
+			// 同批其它 key 会在下次请求重新 SADD,flusher 读 Redis 当前累计绝对值刷库即自愈
+			// (Redis 仍是 enforcement 权威;DB 仅展示)。
 			s.metrics.FlushFKViolationTotal.Add(1)
 			s.metrics.FlushErrorTotal.Add(1)
 			logger.LegacyPrintf("quota_flusher", "[QuotaFlusher] FK violation (dropped %d snaps): %v", len(snaps), writeErr)
diff --git a/backend/internal/service/user_platform_quota_port.go b/backend/internal/service/user_platform_quota_port.go
index 0f88eda4c3..828e7a9636 100644
--- a/backend/internal/service/user_platform_quota_port.go
+++ b/backend/internal/service/user_platform_quota_port.go
@@ -11,8 +11,8 @@ import (
 // handler 只需引用 service 包，无需直接依赖 repository 包。
 var ErrUserPlatformQuotaNotFound = errors.New("user platform quota not found")
 
-// ErrUserPlatformQuotaFKViolation service 层 sentinel：批量 snapshot UPSERT 时存在
-// user_id 不在 users 表的记录（外键违反）。adapter 负责将 repository 层同名 sentinel 包装为此错误。
+// ErrUserPlatformQuotaFKViolation service 层 sentinel：批量快照写入命中了 user_id 不在 users 表的记录。
+// adapter 负责将 repository 层同名 sentinel 包装为此错误。
 var ErrUserPlatformQuotaFKViolation = errors.New("user platform quota snapshot FK violation")
 
 // UserPlatformQuotaSnapshot 是 service 层 flusher 向 DB 写入快照时使用的传输结构。
@@ -44,26 +44,33 @@ type UserPlatformQuotaRecord struct {
 	MonthlyWindowStart *time.Time
 }
 
+// HasAnyLimit 报告该记录是否至少配置了一档限额（0 也算配置）。
+// 三档全空的记录视为未配置：不写入 user_platform_quotas，等价于不限额。
+func (r UserPlatformQuotaRecord) HasAnyLimit() bool {
+	return r.DailyLimitUSD != nil || r.WeeklyLimitUSD != nil || r.MonthlyLimitUSD != nil
+}
+
 // UserPlatformQuotaRepository 定义 service 层所需的 user × platform quota 数据访问端口。
 // repository 包的 userPlatformQuotaRepository 实现此接口。
 type UserPlatformQuotaRepository interface {
 	// GetByUserPlatform 查询单条配额记录，未找到时返回 (nil, nil)。
 	GetByUserPlatform(ctx context.Context, userID int64, platform string) (*UserPlatformQuotaRecord, error)
-	// BulkInsertInitial 幂等批量插入初始配额记录（ON CONFLICT DO NOTHING）。
+	// BulkInsertInitial 幂等批量插入初始配额记录：冲突时只补既有行为 NULL 的档位；三档全空的记录跳过。
 	BulkInsertInitial(ctx context.Context, records []UserPlatformQuotaRecord) error
-	// IncrementUsageWithReset 原子地累加用量，若窗口已过期则先重置再累加。
+	// IncrementUsageWithReset 原子地累加用量，若窗口已过期则先重置再累加；记录不存在时不建行、直接返回 nil。
 	IncrementUsageWithReset(ctx context.Context, userID int64, platform string, cost float64, now time.Time) error
 	// ListByUser 查询用户的所有平台配额记录。
 	ListByUser(ctx context.Context, userID int64) ([]UserPlatformQuotaRecord, error)
 	// UpsertForUser 全量替换该用户所有平台限额配置（事务内）：
-	//   1. 软删除未在 records 中出现的所有 active 行
-	//   2. 对 records 中每条：UPDATE 已存在的（含重新激活软删行）；UPDATE 未命中时 INSERT
-	//      仅改 *_limit_usd + deleted_at + updated_at，保留 *_usage_usd / *_window_start。
+	//   1. 软删除未在 records 中出现、或在 records 中但三档全空的所有 active 行
+	//   2. 对每条至少配置了一档限额的 record：UPDATE 已存在的 active 行；未命中时 INSERT
+	//      仅改 *_limit_usd + updated_at，保留 *_usage_usd / *_window_start。
+	// 清空某平台的限额即软删该行并放弃其累计用量；之后再次配置限额会新建行、从新窗口起算。
 	// records 为空时仅执行步骤 1。
 	UpsertForUser(ctx context.Context, userID int64, records []UserPlatformQuotaRecord) error
 	// ResetExpiredWindow 重置指定窗口（"daily"|"weekly"|"monthly"）的用量与起始时间。
 	// 未命中活跃记录时返回（service-side wrapper of repository.ErrUserPlatformQuotaNotFound）。
 	ResetExpiredWindow(ctx context.Context, userID int64, platform string, window string, newStart time.Time) error
-	// BatchSnapshotUsage 绝对值覆盖写入整批 usage 快照。FK 违反返回 ErrUserPlatformQuotaFKViolation。
+	// BatchSnapshotUsage 绝对值覆盖写入整批 usage 快照到既有活跃行；行不存在或已软删的 (user,platform) 跳过。
 	BatchSnapshotUsage(ctx context.Context, snapshots []UserPlatformQuotaSnapshot, now time.Time) error
 }
diff --git a/backend/migrations/238_purge_unlimited_user_platform_quotas.sql b/backend/migrations/238_purge_unlimited_user_platform_quotas.sql
new file mode 100644
index 0000000000..34979b0de3
--- /dev/null
+++ b/backend/migrations/238_purge_unlimited_user_platform_quotas.sql
@@ -0,0 +1,10 @@
+-- user_platform_quotas 仅保存至少配置了一档限额的记录；不存在的行等价于不限额。
+-- 三档限额全为 NULL 的行不携带任何可执行的限额，也不参与任何读取，直接删除。
+-- 幂等：重复执行影响 0 行。
+-- 行数约为历史用户数 × 平台数，整条语句在一个事务内执行；超大表需按
+-- SETUP_MIGRATION_TIMEOUT_SECONDS 调高迁移超时，或在升级前预先分批清理。
+
+DELETE FROM user_platform_quotas
+ WHERE daily_limit_usd IS NULL
+   AND weekly_limit_usd IS NULL
+   AND monthly_limit_usd IS NULL;
diff --git a/backend/migrations/user_platform_quota_purge_unlimited_migration_test.go b/backend/migrations/user_platform_quota_purge_unlimited_migration_test.go
new file mode 100644
index 0000000000..fdc5e65df8
--- /dev/null
+++ b/backend/migrations/user_platform_quota_purge_unlimited_migration_test.go
@@ -0,0 +1,27 @@
+package migrations
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestUserPlatformQuotasPurgeUnlimitedMigration 校验 238 号迁移只删除三档限额全为 NULL 的行：
+// 这类行等价于"不存在"，任何一档非 NULL 的记录（含软删历史）都必须保留。
+func TestUserPlatformQuotasPurgeUnlimitedMigration(t *testing.T) {
+	content, err := FS.ReadFile("238_purge_unlimited_user_platform_quotas.sql")
+	require.NoError(t, err)
+
+	// 去掉注释行后只允许这一条 DELETE。
+	var stmts []string
+	for _, line := range strings.Split(string(content), "\n") {
+		trimmed := strings.TrimSpace(line)
+		if trimmed == "" || strings.HasPrefix(trimmed, "--") {
+			continue
+		}
+		stmts = append(stmts, trimmed)
+	}
+	sql := strings.Join(stmts, " ")
+	require.Equal(t, "DELETE FROM user_platform_quotas WHERE daily_limit_usd IS NULL AND weekly_limit_usd IS NULL AND monthly_limit_usd IS NULL;", sql)
+}
diff --git a/frontend/src/components/admin/user/UserPlatformQuotaModal.vue b/frontend/src/components/admin/user/UserPlatformQuotaModal.vue
index 7121b8e02d..536f9a8424 100644
--- a/frontend/src/components/admin/user/UserPlatformQuotaModal.vue
+++ b/frontend/src/components/admin/user/UserPlatformQuotaModal.vue
@@ -43,8 +43,8 @@
                   <button
                     type="button"
                     class="text-xs text-gray-400 hover:text-amber-500 disabled:opacity-50"
-                    :disabled="!!resetting[`${row.platform}.daily`]"
-                    :title="t('admin.users.platformQuota.reset.button')"
+                    :disabled="!!resetting[`${row.platform}.daily`] || !savedConfigured.has(row.platform)"
+                    :title="t(savedConfigured.has(row.platform) ? 'admin.users.platformQuota.reset.button' : 'admin.users.platformQuota.reset.unavailable')"
                     @click="onReset(row.platform, 'daily')"
                   >↻</button>
                 </div>
@@ -62,8 +62,8 @@
                   <button
                     type="button"
                     class="text-xs text-gray-400 hover:text-amber-500 disabled:opacity-50"
-                    :disabled="!!resetting[`${row.platform}.weekly`]"
-                    :title="t('admin.users.platformQuota.reset.button')"
+                    :disabled="!!resetting[`${row.platform}.weekly`] || !savedConfigured.has(row.platform)"
+                    :title="t(savedConfigured.has(row.platform) ? 'admin.users.platformQuota.reset.button' : 'admin.users.platformQuota.reset.unavailable')"
                     @click="onReset(row.platform, 'weekly')"
                   >↻</button>
                 </div>
@@ -81,8 +81,8 @@
                   <button
                     type="button"
                     class="text-xs text-gray-400 hover:text-amber-500 disabled:opacity-50"
-                    :disabled="!!resetting[`${row.platform}.monthly`]"
-                    :title="t('admin.users.platformQuota.reset.button')"
+                    :disabled="!!resetting[`${row.platform}.monthly`] || !savedConfigured.has(row.platform)"
+                    :title="t(savedConfigured.has(row.platform) ? 'admin.users.platformQuota.reset.button' : 'admin.users.platformQuota.reset.unavailable')"
                     @click="onReset(row.platform, 'monthly')"
                   >↻</button>
                 </div>
@@ -148,6 +148,18 @@ const loading = ref(false)
 const submitting = ref(false)
 const resetting = reactive<Record<string, boolean>>({})
 const quotas = ref<QuotaRow[]>([])
+// 已保存且至少配置了一档限额的平台。只有这些平台在后端有配额记录，重置用量窗口才有对象。
+const savedConfigured = ref<Set<PlatformQuotaPlatform>>(new Set())
+
+function configuredPlatforms(items: PlatformQuotaItem[]): Set<PlatformQuotaPlatform> {
+  const out = new Set<PlatformQuotaPlatform>()
+  for (const it of items) {
+    if (it.daily_limit_usd != null || it.weekly_limit_usd != null || it.monthly_limit_usd != null) {
+      out.add(it.platform)
+    }
+  }
+  return out
+}
 
 function emptyRow(p: PlatformQuotaPlatform): QuotaRow {
   return {
@@ -190,9 +202,11 @@ async function load() {
   try {
     const data = await adminAPI.users.getPlatformQuotas(props.user.id)
     quotas.value = normalize(data.platform_quotas || [])
+    savedConfigured.value = configuredPlatforms(data.platform_quotas || [])
   } catch {
     appStore.showError(t('admin.users.platformQuota.loadFailed'))
     quotas.value = PLATFORMS.map(emptyRow)
+    savedConfigured.value = new Set()
   } finally {
     loading.value = false
   }
@@ -273,6 +287,7 @@ async function onReset(platform: PlatformQuotaPlatform, quotaWindow: PlatformQuo
   try {
     const data = await adminAPI.users.resetPlatformQuotaWindow(props.user.id, platform, quotaWindow)
     quotas.value = normalize(data.platform_quotas || [])
+    savedConfigured.value = configuredPlatforms(data.platform_quotas || [])
     appStore.showSuccess(t('admin.users.platformQuota.reset.success', { platform, window: windowLabel }))
   } catch (e: any) {
     appStore.showError(e?.response?.data?.message || t('admin.users.platformQuota.reset.failed'))
diff --git a/frontend/src/components/admin/user/__tests__/UserPlatformQuotaModal.spec.ts b/frontend/src/components/admin/user/__tests__/UserPlatformQuotaModal.spec.ts
index 4315293907..d582126294 100644
--- a/frontend/src/components/admin/user/__tests__/UserPlatformQuotaModal.spec.ts
+++ b/frontend/src/components/admin/user/__tests__/UserPlatformQuotaModal.spec.ts
@@ -168,7 +168,42 @@ describe('UserPlatformQuotaModal', () => {
     confirmSpy.mockRestore()
   })
 
+  // 只有已保存限额的平台在后端有配额记录，重置按钮才可用
+  const anthropicConfigured = {
+    platform_quotas: [
+      {
+        platform: 'anthropic',
+        daily_limit_usd: 10,
+        weekly_limit_usd: null,
+        monthly_limit_usd: null,
+        daily_usage_usd: 0,
+        weekly_usage_usd: 0,
+        monthly_usage_usd: 0,
+      },
+    ],
+  }
+
+  it('未配置限额的平台重置按钮禁用并提示不可用', async () => {
+    const w = await mountAndOpen()
+    const resetBtns = w.findAll('button').filter((b) => b.text() === '↻')
+    expect(resetBtns.length).toBe(15) // 5 平台 × 3 窗口
+    for (const b of resetBtns) {
+      expect((b.element as HTMLButtonElement).disabled).toBe(true)
+      expect(b.attributes('title')).toBe('admin.users.platformQuota.reset.unavailable')
+    }
+  })
+
+  it('已保存限额的平台重置按钮可用，其余仍禁用', async () => {
+    apiMocks.getPlatformQuotas.mockResolvedValue(anthropicConfigured)
+    const w = await mountAndOpen()
+    const resetBtns = w.findAll('button').filter((b) => b.text() === '↻')
+    const enabled = resetBtns.filter((b) => !(b.element as HTMLButtonElement).disabled)
+    expect(enabled.length).toBe(3) // anthropic 的 daily/weekly/monthly
+    expect(enabled[0].attributes('title')).toBe('admin.users.platformQuota.reset.button')
+  })
+
   it('重置按钮 confirm 取消则不调用 API', async () => {
+    apiMocks.getPlatformQuotas.mockResolvedValue(anthropicConfigured)
     const confirmSpy = vi.spyOn(window, 'confirm').mockReturnValue(false)
     const w = await mountAndOpen()
     const resetBtns = w.findAll('button').filter((b) => b.text() === '↻')
@@ -180,6 +215,7 @@ describe('UserPlatformQuotaModal', () => {
   })
 
   it('重置按钮 confirm 确认则调用 API', async () => {
+    apiMocks.getPlatformQuotas.mockResolvedValue(anthropicConfigured)
     const confirmSpy = vi.spyOn(window, 'confirm').mockReturnValue(true)
     const w = await mountAndOpen()
     const resetBtns = w.findAll('button').filter((b) => b.text() === '↻')
diff --git a/frontend/src/components/user/dashboard/UserDashboardStats.vue b/frontend/src/components/user/dashboard/UserDashboardStats.vue
index ad9fae1ff4..293172bf8f 100644
--- a/frontend/src/components/user/dashboard/UserDashboardStats.vue
+++ b/frontend/src/components/user/dashboard/UserDashboardStats.vue
@@ -137,13 +137,15 @@
     <div class="mb-3 flex items-center justify-between">
       <h3 class="text-sm font-semibold text-gray-900 dark:text-white">{{ t('dashboard.platformBreakdown') }}</h3>
       <span class="text-xs text-gray-500 dark:text-gray-400">
-        {{ t('dashboard.platformCount', { count: sortedPlatforms.length }) }}
+        {{ t('dashboard.platformCount', { count: platformCount }) }}
       </span>
     </div>
     <div class="grid grid-cols-1 gap-3 sm:grid-cols-2 lg:grid-cols-4">
       <div
         v-for="item in platformCards"
         :key="item.platform"
+        data-testid="platform-card"
+        :data-platform="item.platform"
         :class="[
           'rounded-lg border p-3',
           item.isOther
@@ -226,7 +228,7 @@
 import { computed } from 'vue'
 import { useI18n } from 'vue-i18n'
 import Icon from '@/components/icons/Icon.vue'
-import type { UserDashboardStats as UserStatsType } from '@/api/usage'
+import type { PlatformDashboardStats, UserDashboardStats as UserStatsType } from '@/api/usage'
 import type { PlatformQuotaItem } from '@/types'
 
 interface FusedPlatformCard {
@@ -261,27 +263,27 @@ const PLATFORM_LABELS: Record<string, string> = {
 
 const platformLabel = (p: string) => PLATFORM_LABELS[p] ?? p
 
-const sortedPlatforms = computed(() => {
-  const list = props.stats?.by_platform ?? []
-  return [...list].sort((a, b) => b.total_actual_cost - a.total_actual_cost)
-})
-
 // 处理"各平台之和 < 总值"的差值：后端按平台聚合时过滤了无法归属平台的行
 // （group 与 account 都缺 platform）。这里把差值作为"其他"卡片显式展示，
 // 避免 Row 1 总值与 Row 3 平台拆分加总对不上、用户困惑。
 const OTHER_THRESHOLD = 0.0001
 const platformCards = computed<FusedPlatformCard[]>(() => {
   // 建立 by_platform Map
-  const byPlat = new Map<string, (typeof sortedPlatforms.value)[number]>()
+  const byPlat = new Map<string, PlatformDashboardStats>()
   for (const item of props.stats?.by_platform ?? []) byPlat.set(item.platform, item)
 
-  // 建立 quota Map
+  // 建立 quota Map。三档全空的记录不产生卡片，挂到卡片上也不渲染配额区。
   const byQuota = new Map<string, PlatformQuotaItem>()
   for (const q of props.platformQuotas ?? []) byQuota.set(q.platform, q)
 
-  // union 平台集合。后端 by_platform / quota 接口均不会返回 platform='__other__'，
+  // 卡片集合 = 有用量的平台 ∪ 至少配置了一档限额的平台。
+  // 三档全空的限额记录等价于不限额，不单独产生卡片。
+  // 后端 by_platform / quota 接口均不会返回 platform='__other__'，
   // 无需显式排除；__other__ 由下方差值补差逻辑单独追加。
-  const platforms = new Set<string>([...byPlat.keys(), ...byQuota.keys()])
+  const platforms = new Set<string>(byPlat.keys())
+  for (const [platform, q] of byQuota) {
+    if (hasAnyLimit(q)) platforms.add(platform)
+  }
 
   const PLATFORM_ORDER = ['anthropic', 'openai', 'gemini', 'antigravity', 'grok']
   const cards: FusedPlatformCard[] = []
@@ -330,6 +332,9 @@ const platformCards = computed<FusedPlatformCard[]>(() => {
   return cards
 })
 
+// 标题右侧的平台计数 = 实际渲染的平台卡片数，不含"其他"差额卡。
+const platformCount = computed(() => platformCards.value.filter((c) => !c.isOther).length)
+
 // Quota helpers
 
 type QuotaWindow = 'daily' | 'weekly' | 'monthly'
diff --git a/frontend/src/components/user/dashboard/__tests__/UserDashboardStats.spec.ts b/frontend/src/components/user/dashboard/__tests__/UserDashboardStats.spec.ts
new file mode 100644
index 0000000000..a2ab9ed5cf
--- /dev/null
+++ b/frontend/src/components/user/dashboard/__tests__/UserDashboardStats.spec.ts
@@ -0,0 +1,154 @@
+import { describe, it, expect, vi } from 'vitest'
+import { mount, type VueWrapper } from '@vue/test-utils'
+
+// t() 回显 key；带参数时附上 JSON，便于断言计数
+vi.mock('vue-i18n', async () => {
+  const actual = await vi.importActual<typeof import('vue-i18n')>('vue-i18n')
+  return {
+    ...actual,
+    useI18n: () => ({
+      t: (key: string, params?: Record<string, unknown>) =>
+        params ? `${key}:${JSON.stringify(params)}` : key,
+    }),
+  }
+})
+
+import UserDashboardStats from '../UserDashboardStats.vue'
+import type { UserDashboardStats as UserStatsType, PlatformDashboardStats } from '@/api/usage'
+import type { PlatformQuotaItem } from '@/types'
+
+function makeStats(over: Partial<UserStatsType> = {}): UserStatsType {
+  return {
+    total_api_keys: 1,
+    active_api_keys: 1,
+    total_requests: 0,
+    total_input_tokens: 0,
+    total_output_tokens: 0,
+    total_cache_creation_tokens: 0,
+    total_cache_read_tokens: 0,
+    total_tokens: 0,
+    total_cost: 0,
+    total_actual_cost: 0,
+    today_requests: 0,
+    today_input_tokens: 0,
+    today_output_tokens: 0,
+    today_cache_creation_tokens: 0,
+    today_cache_read_tokens: 0,
+    today_tokens: 0,
+    today_cost: 0,
+    today_actual_cost: 0,
+    average_duration_ms: 0,
+    rpm: 0,
+    tpm: 0,
+    by_platform: [],
+    ...over,
+  }
+}
+
+function usage(platform: string, cost: number): PlatformDashboardStats {
+  return {
+    platform,
+    total_requests: 1,
+    total_tokens: 10,
+    total_actual_cost: cost,
+    today_requests: 1,
+    today_tokens: 10,
+    today_actual_cost: cost,
+  }
+}
+
+function quota(over: Partial<PlatformQuotaItem> & { platform: string }): PlatformQuotaItem {
+  return {
+    daily_limit_usd: null,
+    weekly_limit_usd: null,
+    monthly_limit_usd: null,
+    daily_usage_usd: 0,
+    weekly_usage_usd: 0,
+    monthly_usage_usd: 0,
+    ...over,
+  } as PlatformQuotaItem
+}
+
+function mountStats(stats: UserStatsType, platformQuotas: PlatformQuotaItem[] | null = null, isSimple = false) {
+  return mount(UserDashboardStats, {
+    props: { stats, balance: 0, isSimple, platformQuotas },
+    global: { stubs: { Icon: true } },
+  })
+}
+
+/** 渲染出的平台卡片，按 DOM 顺序返回 data-platform */
+function cardPlatforms(w: VueWrapper): string[] {
+  return w.findAll('[data-testid="platform-card"]').map((c) => c.attributes('data-platform') ?? '')
+}
+
+describe('UserDashboardStats 按平台拆分', () => {
+  it('只有用量的平台才产生卡片；三档全空的限额记录不产生卡片', () => {
+    const w = mountStats(
+      makeStats({ total_actual_cost: 0.03, today_actual_cost: 0.03, by_platform: [usage('grok', 0.03)] }),
+      [
+        quota({ platform: 'anthropic' }),
+        quota({ platform: 'openai' }),
+        quota({ platform: 'gemini' }),
+        quota({ platform: 'grok' }),
+      ]
+    )
+    expect(cardPlatforms(w)).toEqual(['grok'])
+    expect(w.text()).toContain('dashboard.platformCount:{"count":1}')
+    expect(w.html()).not.toContain('dashboard.platformQuota.title')
+  })
+
+  it('配置了限额但没有用量的平台也产生卡片，并渲染配额区', () => {
+    const w = mountStats(
+      makeStats({ total_actual_cost: 0.03, today_actual_cost: 0.03, by_platform: [usage('grok', 0.03)] }),
+      [quota({ platform: 'openai', daily_limit_usd: 10, daily_usage_usd: 2.5 }), quota({ platform: 'anthropic' })]
+    )
+    // 固定顺序：openai 排在 grok 前
+    expect(cardPlatforms(w)).toEqual(['openai', 'grok'])
+    expect(w.text()).toContain('dashboard.platformQuota.title')
+    expect(w.text()).toContain('dashboard.platformCount:{"count":2}')
+  })
+
+  it('同一平台既有用量又有限额只产生一张卡片', () => {
+    const w = mountStats(
+      makeStats({ total_actual_cost: 1, today_actual_cost: 1, by_platform: [usage('openai', 1)] }),
+      [quota({ platform: 'openai', daily_limit_usd: 10, daily_usage_usd: 1 })]
+    )
+    expect(cardPlatforms(w)).toEqual(['openai'])
+    expect(w.text()).toContain('dashboard.platformQuota.title')
+  })
+
+  it('限额为 0 的平台视为已配置，渲染禁用态', () => {
+    const w = mountStats(makeStats(), [quota({ platform: 'gemini', weekly_limit_usd: 0 })])
+    expect(cardPlatforms(w)).toEqual(['gemini'])
+    expect(w.text()).toContain('dashboard.platformQuota.disabled')
+    expect(w.text()).toContain('dashboard.platformCount:{"count":1}')
+  })
+
+  it('固定顺序之外的平台也产生卡片，并排在固定顺序之后', () => {
+    const w = mountStats(
+      makeStats({ total_actual_cost: 0.5, today_actual_cost: 0, by_platform: [usage('kimi', 0.3), usage('anthropic', 0.2)] })
+    )
+    expect(cardPlatforms(w)).toEqual(['anthropic', 'kimi'])
+    expect(w.text()).toContain('Kimi')
+  })
+
+  it('总值大于各平台之和时追加"其他"卡片，且不计入平台计数', () => {
+    const w = mountStats(
+      makeStats({ total_actual_cost: 1.0, today_actual_cost: 0, by_platform: [usage('anthropic', 0.4)] })
+    )
+    expect(cardPlatforms(w)).toEqual(['anthropic', '__other__'])
+    expect(w.text()).toContain('dashboard.platformOther')
+    expect(w.text()).toContain('dashboard.platformCount:{"count":1}')
+  })
+
+  it('没有任何用量也没有配置限额时不渲染整块', () => {
+    const w = mountStats(makeStats(), [quota({ platform: 'anthropic' }), quota({ platform: 'openai' })])
+    expect(w.html()).not.toContain('dashboard.platformBreakdown')
+    expect(cardPlatforms(w)).toEqual([])
+  })
+
+  it('简易模式不渲染整块', () => {
+    const w = mountStats(makeStats({ by_platform: [usage('openai', 1)] }), null, true)
+    expect(w.html()).not.toContain('dashboard.platformBreakdown')
+  })
+})
diff --git a/frontend/src/i18n/locales/en/admin/overview.ts b/frontend/src/i18n/locales/en/admin/overview.ts
index 18e9318abe..f81b1ced93 100644
--- a/frontend/src/i18n/locales/en/admin/overview.ts
+++ b/frontend/src/i18n/locales/en/admin/overview.ts
@@ -758,6 +758,7 @@ export default {
         clearAllConfirm: 'Clear daily / weekly / monthly limits for ALL platforms? All platforms will become "unlimited" with no local undo — you must manually re-enter values before saving.',
         reset: {
           button: 'Reset window',
+          unavailable: 'No limit configured for this platform, so there is no usage window to reset',
           confirm: 'Reset the {window} usage for {platform} for this user? This is effective immediately.',
           success: 'Reset {platform} {window} usage',
           failed: 'Reset failed',
diff --git a/frontend/src/i18n/locales/en/admin/settings.ts b/frontend/src/i18n/locales/en/admin/settings.ts
index da509a8251..534f79d617 100644
--- a/frontend/src/i18n/locales/en/admin/settings.ts
+++ b/frontend/src/i18n/locales/en/admin/settings.ts
@@ -407,7 +407,7 @@ export default {
         subscriptionGroup: 'Subscription Group',
         subscriptionValidityDays: 'Validity (days)',
         defaultPlatformQuotas: 'Default Platform Quotas (on signup)',
-        defaultPlatformQuotasHint: 'Automatically assigned to new users on signup; existing users are not affected. Leave blank = unlimited.',
+        defaultPlatformQuotasHint: 'Applied to new users on signup; existing users are not affected. Leave blank = no limit for that platform and window.',
         platformQuotaNotice: 'Monthly quota uses a 30-day rolling window, not a calendar month.',
       },
       platformQuota: {
diff --git a/frontend/src/i18n/locales/zh/admin/overview.ts b/frontend/src/i18n/locales/zh/admin/overview.ts
index 8eca58fe35..d7ba0942f6 100644
--- a/frontend/src/i18n/locales/zh/admin/overview.ts
+++ b/frontend/src/i18n/locales/zh/admin/overview.ts
@@ -755,6 +755,7 @@ export default {
         clearAllConfirm: '确认清空全部平台的日 / 周 / 月限额？所有平台将变为"无限额"，本地无法撤销，需要在保存前手动重填。',
         reset: {
           button: '重置该窗口',
+          unavailable: '该平台未配置限额，没有可重置的用量窗口',
           confirm: '确认重置该用户 {platform} 平台的 {window} 用量？此操作立即生效。',
           success: '已重置 {platform} {window} 用量',
           failed: '重置失败',
diff --git a/frontend/src/i18n/locales/zh/admin/settings.ts b/frontend/src/i18n/locales/zh/admin/settings.ts
index 5bdedb0104..fd2530daba 100644
--- a/frontend/src/i18n/locales/zh/admin/settings.ts
+++ b/frontend/src/i18n/locales/zh/admin/settings.ts
@@ -402,7 +402,7 @@ export default {
         subscriptionGroup: '订阅分组',
         subscriptionValidityDays: '有效期（天）',
         defaultPlatformQuotas: '默认平台限额（注册时分配）',
-        defaultPlatformQuotasHint: '新用户注册时自动写入平台限额记录；已有用户不受影响。留空 = 该平台该窗口不限制。',
+        defaultPlatformQuotasHint: '新用户注册时自动获得这里配置的限额；已有用户不受影响。留空 = 该平台该窗口不限制。',
         platformQuotaNotice: '月限额为 30 天滚动窗口，非自然月',
       },
       platformQuota: {