security: fix rate-limit bypass, payment amount check, stats leak, owner-dir collision, video panic guard

- clientIP: stop trusting client-supplied X-Forwarded-For; use gin ClientIP
  with trusted proxies limited to private docker networks
- payment: verify notify money matches order amount; remove hardcoded
  gateway default, fail loudly when api_base is unset
- stats: public endpoint now serves aggregates only; recent files (owner
  names) moved to admin-only /stats/recent
- auth: reject signups whose username/email-local collides with another
  user's media directory namespace
- v1: recover panics in background video jobs, refund + mark failed

backend/internal/service/admin_read.go

@@ -221,7 +221,6 @@ func (s *AdminReadService) Stats(ctx context.Context) (map[string]any, error) {
 	if err != nil {
 		return nil, err
 	}
-	recentFiles, _ := s.RecentImages(ctx, 24)
 	files, _, _ := s.scanGeneratedFiles(ctx)
 	// Exclude homepage showcase media so 已生成作品 matches the 作品管理 total.
 	pinned := map[string]struct{}{}
@@ -239,15 +238,26 @@ func (s *AdminReadService) Stats(ctx context.Context) (map[string]any, error) {
 		count++
 		size += f.Size
 	}
+	// Aggregate-only: `recent` (owner dirs + filenames) is served via
+	// StatsRecent behind an admin session — it must not leak publicly.
 	return map[string]any{
 		"generated_count":      count,
 		"generated_size_bytes": size,
-		"recent":               recentFiles,
 		"avg_elapsed_ms":       stats.AvgElapsedMS,
 		"avg_elapsed_ms_24h":   stats.AvgElapsedMS24,
 	}, nil
 }
 
+// StatsRecent backs the admin image picker; the route lives in the
+// RequireAdminSession group because entries carry per-user owner names.
+func (s *AdminReadService) StatsRecent(ctx context.Context) (map[string]any, error) {
+	recentFiles, err := s.RecentImages(ctx, 24)
+	if err != nil {
+		return nil, err
+	}
+	return map[string]any{"recent": recentFiles}, nil
+}
+
 // Dashboard assembles the admin overview's analytics entirely server-side
 // (event windows, hourly trend, top models/failures/spenders) plus CDK / invite
 // / checkin summaries. This replaces the old client-side math over the last 200

backend/internal/service/auth.go

@@ -100,6 +100,34 @@ func ownsImageDir(user *model.User, owner string) bool {
 	return false
 }
 
+// checkOwnerDirCollision rejects a signup whose sanitized username or email
+// local-part collides with any existing user's directory candidates. Media
+// authorization (ownsImageDir) matches on those candidates, so without this
+// check registering as <victim-name>@any-domain would grant access to the
+// victim's /images/<name>/ directory.
+func (s *AuthService) checkOwnerDirCollision(ctx context.Context, username, email string) error {
+	newName := sanitizeOwnerName(username)
+	newEmail := sanitizeOwnerName(strings.Split(email, "@")[0])
+	if newName == "" && newEmail == "" {
+		return nil
+	}
+	users, err := s.users.ListOwnerCandidates(ctx)
+	if err != nil {
+		return err
+	}
+	for _, u := range users {
+		oldName := sanitizeOwnerName(u.Name)
+		oldEmail := sanitizeOwnerName(strings.Split(u.Email, "@")[0])
+		if newName != "" && (oldName == newName || oldEmail == newName) {
+			return errors.New("用户名与已有用户冲突,请更换")
+		}
+		if newEmail != "" && newName != newEmail && (oldName == newEmail || oldEmail == newEmail) {
+			return errors.New("邮箱前缀与已有用户冲突,请更换")
+		}
+	}
+	return nil
+}
+
 func (s *AuthService) CurrentUserFromBearer(ctx context.Context, authHeader string) (*model.User, *SessionPayload, error) {
 	token := ParseBearer(authHeader)
 	return s.currentUserFromToken(ctx, token)
@@ -272,6 +300,9 @@ func (s *AuthService) Register(ctx context.Context, email, username, password, i
 	if exists {
 		return nil, "", nil, errors.New("用户名已存在")
 	}
+	if err := s.checkOwnerDirCollision(ctx, normalizedUsername, normalizedEmail); err != nil {
+		return nil, "", nil, err
+	}
 
 	passwordHash, err := HashPassword(password)
 	if err != nil {

backend/internal/service/payment.go

@@ -55,9 +55,6 @@ func (s *PaymentService) get(ctx context.Context, key string) string {
 
 func (s *PaymentService) Settings(ctx context.Context) PaySettings {
 	api := strings.TrimRight(strings.TrimSpace(s.get(ctx, "pay.api_base")), "/")
-	if api == "" {
-		api = "https://www.ezfpy.cn"
-	}
 	ratio, _ := strconv.Atoi(s.get(ctx, "pay.points_ratio"))
 	if ratio <= 0 {
 		ratio = 100
@@ -147,6 +144,11 @@ func (s *PaymentService) CreateOrder(ctx context.Context, user *model.User, amou
 	if cfg.PID == "" || cfg.Key == "" {
 		return nil, ErrPayNotConfig
 	}
+	// Never guess a gateway: an empty api_base must fail loudly instead of
+	// silently routing signed payment traffic to some hardcoded third party.
+	if cfg.APIBase == "" {
+		return nil, ErrPayNotConfig
+	}
 	if !cfg.allows(method) {
 		return nil, ErrPayMethod
 	}
@@ -227,6 +229,11 @@ func (s *PaymentService) HandleNotify(ctx context.Context, params map[string]str
 	if err != nil || order == nil {
 		return false, ErrOrderNotFound
 	}
+	// The gateway signs whatever the cashier actually collected — verify the
+	// paid amount matches the order, or an underpaid notify credits full points.
+	if money, perr := strconv.ParseFloat(strings.TrimSpace(params["money"]), 64); perr != nil || math.Abs(money-order.Amount) > 0.01 {
+		return false, errors.New("notify amount mismatch")
+	}
 	credited, err := s.orders.MarkPaid(ctx, order.ID, params["trade_no"], time.Now())
 	if err != nil {
 		return false, err

backend/internal/service/v1.go

@@ -10,6 +10,7 @@ import (
 	"log"
 	"net/http"
 	"path/filepath"
+	"runtime/debug"
 	"sort"
 	"strings"
 	"sync"
@@ -969,6 +970,16 @@ func (s *V1Service) runVideoJob(ctx context.Context, principal *APIPrincipal, in
 	defer s.inflight.Done(eventID)
 	startedAt := time.Now()
 
+	// A panic in provider fan-out must fail the event (and refund), not
+	// take down the whole API process with it.
+	defer func() {
+		if r := recover(); r != nil {
+			log.Printf("[v1] panic in runVideoJob event=%s model=%s: %v\n%s", eventID, modelItem.Name, r, debug.Stack())
+			_ = s.refundIfNeeded(ctx, principal, eventID, price)
+			_ = s.events.UpdateStatus(ctx, eventID, "failed", fmt.Sprintf("internal error: %v", r), 0)
+		}
+	}()
+
 	// No-store: capture only the UPSTREAM video URL. /content streams it on demand
 	// (grok URLs are auth-gated → fetched with the generating account's token).
 	var videoURL string