diff --git a/backend/internal/app/chunk_quota_security_test.go b/backend/internal/app/chunk_quota_security_test.go
new file mode 100644
index 000000000..806b76192
--- /dev/null
+++ b/backend/internal/app/chunk_quota_security_test.go
@@ -0,0 +1,58 @@
+package app
+
+import (
+	"bytes"
+	"testing"
+	"time"
+)
+
+func TestChunkQuotaRejectsSingleFileLimit(t *testing.T) {
+	svc := newResourceTestService(t)
+	if _, err := svc.reserveChunkedUploadQuota("user-1", megabytes(defaultRuntimePolicy().Resource.ResourceUploadMB)); err == nil {
+		t.Fatal("chunked upload accepted a file at the exclusive single-file limit")
+	}
+}
+
+func TestChunkQuotaReservedUploadConsumesOnce(t *testing.T) {
+	svc := newResourceTestService(t)
+	if err := svc.ReserveChunkUploadSession("user", "session", 7, time.Now().Add(time.Hour), 32); err != nil {
+		t.Fatal(err)
+	}
+	day := time.Now().UTC().Format("2006-01-02")
+	if used, _ := svc.repo.DailyUploadBytes("user", day); used != 7 {
+		t.Fatalf("quota before receiving bytes=%d", used)
+	}
+	resource, err := svc.UploadReservedResourceFile("user", "session", "test.txt", 7, "file", 0, 0, 0, bytes.NewReader([]byte("payload")), "logical-key")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resource.Size != 7 {
+		t.Fatalf("size=%d", resource.Size)
+	}
+	if used, _ := svc.repo.DailyUploadBytes("user", day); used != 7 {
+		t.Fatalf("quota after completion=%d", used)
+	}
+	if err := svc.ReserveChunkUploadSession("user", "retry", 7, time.Now().Add(time.Hour), 32); err != nil {
+		t.Fatal(err)
+	}
+	reused, err := svc.UploadReservedResourceFile("user", "retry", "test.txt", 7, "file", 0, 0, 0, bytes.NewReader([]byte("payload")), "logical-key")
+	if err != nil || reused.ID != resource.ID {
+		t.Fatalf("retry=%v err=%v", reused, err)
+	}
+	if used, _ := svc.repo.DailyUploadBytes("user", day); used != 7 {
+		t.Fatalf("quota after replay=%d", used)
+	}
+}
+
+func TestChunkQuotaFailedCompletionReleases(t *testing.T) {
+	svc := newResourceTestService(t)
+	if err := svc.ReserveChunkUploadSession("user", "failed", 7, time.Now().Add(time.Hour), 32); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := svc.UploadReservedResourceFile("user", "failed", "test.txt", 7, "file", 0, 0, 0, nil); err == nil {
+		t.Fatal("nil file accepted")
+	}
+	if used, _ := svc.repo.DailyUploadBytes("user", time.Now().UTC().Format("2006-01-02")); used != 0 {
+		t.Fatalf("failed upload retained quota=%d", used)
+	}
+}
diff --git a/backend/internal/app/resource_oss_fallback_test.go b/backend/internal/app/resource_oss_fallback_test.go
index cc944b004..7da11c47b 100644
--- a/backend/internal/app/resource_oss_fallback_test.go
+++ b/backend/internal/app/resource_oss_fallback_test.go
@@ -21,6 +21,7 @@ func newResourceFallbackTestService(t *testing.T) (*Service, *gorm.DB) {
 	}
 	if err := db.AutoMigrate(
 		&model.Resource{},
+		&model.UploadReservation{},
 		&model.UserOSSSetting{},
 		&model.SystemSetting{},
 		&model.StorageLocation{},
diff --git a/backend/internal/app/resource_store.go b/backend/internal/app/resource_store.go
index f958f307d..44c235f64 100644
--- a/backend/internal/app/resource_store.go
+++ b/backend/internal/app/resource_store.go
@@ -11,6 +11,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log"
 	"mime/multipart"
 	"net/http"
 	"os"
@@ -79,9 +80,24 @@ func (s *Service) uploadResource(userID string, header *multipart.FileHeader, ki
 }
 
 // UploadResourceFile 接收已完整落盘的本地文件（分片上传合并后调用）。
-// 它与 UploadResource 共享资源幂等、媒体探测、配额和持久化语义，唯一差异是分片会话已在 handler 校验单文件上限，
-// 因而此处不再重复该上限检查；uploadIdentity 用于跨请求重试时复用同一逻辑资源，避免重复对象。
+// 它与 UploadResource 共享资源幂等、媒体探测、配额和持久化语义。
 func (s *Service) UploadResourceFile(userID string, fileName string, size int64, kind string, width int, height int, durationMs int64, file io.ReadSeeker, uploadIdentity ...string) (*model.Resource, error) {
+	return s.uploadResourceFile(userID, "", fileName, size, kind, width, height, durationMs, file, uploadIdentity...)
+}
+
+func (s *Service) UploadReservedResourceFile(userID, reservationID, fileName string, size int64, kind string, width, height int, durationMs int64, file io.ReadSeeker, uploadIdentity ...string) (*model.Resource, error) {
+	if reservationID == "" {
+		return nil, BadAuthRequest("上传会话不存在")
+	}
+	defer func() {
+		if err := s.ReleaseChunkUploadSession(userID, reservationID); err != nil {
+			log.Printf("release upload session failed: %v", err)
+		}
+	}()
+	return s.uploadResourceFile(userID, reservationID, fileName, size, kind, width, height, durationMs, file, uploadIdentity...)
+}
+
+func (s *Service) uploadResourceFile(userID, reservationID, fileName string, size int64, kind string, width int, height int, durationMs int64, file io.ReadSeeker, uploadIdentity ...string) (*model.Resource, error) {
 	if file == nil || size <= 0 {
 		return nil, BadAuthRequest("请选择要上传的文件")
 	}
@@ -99,8 +115,17 @@ func (s *Service) UploadResourceFile(userID string, fileName string, size int64,
 	}
 	kind = uploadedResourceKind(mimeType)
 	if existing != nil {
+		if reservationID != "" {
+			if err := s.ReleaseChunkUploadSession(userID, reservationID); err != nil {
+				return nil, err
+			}
+		}
 		return s.retryStoredResource(userID, existing, kind, mimeType, size, file)
 	}
+	if reservationID != "" {
+		resource, _, err := s.storeResource(userID, kind, fileName, mimeType, size, width, height, durationMs, file, uploadKey, false, reservationID)
+		return resource, err
+	}
 	day, err := s.reserveChunkedUploadQuota(userID, size)
 	if err != nil {
 		return nil, err
@@ -253,11 +278,15 @@ func (s *Service) openResourceRange(userID string, resource *model.Resource, ran
 	return &ResourceStream{Resource: resource, Body: stream.Body, StatusCode: stream.StatusCode, ContentLength: stream.ContentLength, ContentRange: stream.ContentRange, AcceptRanges: stream.AcceptRanges}, nil
 }
 
-func (s *Service) storeResource(userID string, kind string, fileName string, mimeType string, size int64, width int, height int, durationMs int64, body io.Reader, uploadKey *string, forceLocal bool) (*model.Resource, bool, error) {
-	return s.storeResourceWithWriter(userID, kind, fileName, mimeType, size, width, height, durationMs, body, uploadKey, forceLocal, s.storeResourceObject)
+func (s *Service) storeResource(userID string, kind string, fileName string, mimeType string, size int64, width int, height int, durationMs int64, body io.Reader, uploadKey *string, forceLocal bool, reservationIDs ...string) (*model.Resource, bool, error) {
+	return s.storeResourceWithWriter(userID, kind, fileName, mimeType, size, width, height, durationMs, body, uploadKey, forceLocal, s.storeResourceObject, reservationIDs...)
 }
 
-func (s *Service) storeResourceWithWriter(userID string, kind string, fileName string, mimeType string, size int64, width int, height int, durationMs int64, body io.Reader, uploadKey *string, forceLocal bool, writeObject func(*model.Resource, string, io.Reader) (string, error)) (*model.Resource, bool, error) {
+func (s *Service) storeResourceWithWriter(userID string, kind string, fileName string, mimeType string, size int64, width int, height int, durationMs int64, body io.Reader, uploadKey *string, forceLocal bool, writeObject func(*model.Resource, string, io.Reader) (string, error), reservationIDs ...string) (*model.Resource, bool, error) {
+	reservationID := ""
+	if len(reservationIDs) > 0 {
+		reservationID = reservationIDs[0]
+	}
 	// Live2D is reserved for the administrator's validated local import path.
 	if !(forceLocal && kind == "live2d") {
 		kind = normalizeResourceKind(kind, mimeType)
@@ -321,7 +350,7 @@ func (s *Service) storeResourceWithWriter(userID string, kind string, fileName s
 	}
 	resource.Status = model.ResourceStatusReady
 	resource.ETag = etag
-	if err := s.repo.SaveResource(&resource); err != nil {
+	if err := s.saveResourceWithinStorageLimit(&resource, reservationID); err != nil {
 		cleanupErr := s.deleteStoredResourceObject(userID, &resource)
 		if cleanupErr == nil {
 			if deleteErr := s.repo.DeleteResource(userID, resource.ID); deleteErr != nil {
@@ -435,7 +464,7 @@ func (s *Service) retryStoredResource(userID string, resource *model.Resource, k
 	}
 	resource.Status = model.ResourceStatusReady
 	resource.ETag = etag
-	if err := s.repo.SaveResource(resource); err != nil {
+	if err := s.saveResourceWithinStorageLimit(resource, ""); err != nil {
 		s.releaseRetryUploadQuota(userID, day, size)
 		resource.Status = model.ResourceStatusFailed
 		resource.Error = "保存资源重试就绪状态失败"
diff --git a/backend/internal/app/resource_test.go b/backend/internal/app/resource_test.go
index 1fb64ad40..fd3cb81b3 100644
--- a/backend/internal/app/resource_test.go
+++ b/backend/internal/app/resource_test.go
@@ -934,7 +934,7 @@ func newResourceTestService(t *testing.T) *Service {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if err := db.AutoMigrate(&model.SystemSetting{}, &model.UserOSSSetting{}, &model.StorageLocation{}, &model.UserDailyUploadUsage{}, &model.Resource{}); err != nil {
+	if err := db.AutoMigrate(&model.SystemSetting{}, &model.UserOSSSetting{}, &model.StorageLocation{}, &model.UserDailyUploadUsage{}, &model.Resource{}, &model.UploadReservation{}); err != nil {
 		t.Fatal(err)
 	}
 	return &Service{repo: repository.New(db), dataDir: t.TempDir()}
diff --git a/backend/internal/app/task_media_storage.go b/backend/internal/app/task_media_storage.go
index df253be79..82610e247 100644
--- a/backend/internal/app/task_media_storage.go
+++ b/backend/internal/app/task_media_storage.go
@@ -266,7 +266,7 @@ func (s *Service) storeTaskMediaFile(task *model.Task, index int, path, mimeType
 		resource.ETag, err = s.storeTaskMediaObject(resource, "generated."+extensionFromMimeType(mimeType), file)
 		if err == nil {
 			resource.Status, resource.Error, resource.UpdatedAt = model.ResourceStatusReady, "", time.Now()
-			err = s.repo.SaveResource(resource)
+			err = s.saveResourceWithinStorageLimit(resource, "")
 		}
 	}
 	if err != nil {
diff --git a/backend/internal/app/upload_quota.go b/backend/internal/app/upload_quota.go
index da82588e0..1f29bde40 100644
--- a/backend/internal/app/upload_quota.go
+++ b/backend/internal/app/upload_quota.go
@@ -6,6 +6,7 @@ import (
 	"log"
 	"time"
 
+	"infinite-canvas/backend/internal/model"
 	"infinite-canvas/backend/internal/repository"
 )
 
@@ -18,14 +19,49 @@ func (s *Service) reserveUserUploadQuota(userID string, size int64) (string, err
 	return s.reserveUserStoredFileQuota(userID, size, megabytes(policy.Resource.ResourceUploadMB), megabytes(policy.Resource.DailyUploadMB), gigabytes(policy.Resource.StoredFileGB), fmt.Sprintf("单个上传文件必须小于 %dMB", policy.Resource.ResourceUploadMB))
 }
 
-// reserveChunkedUploadQuota 用于分片上传完成时预留额度：单文件上限对分片会话不适用（每片已独立校验），
-// 仅受“今日上传”与“账号存储总量”约束；singleFileLimit 传 size+1 使单文件上限永不命中。
+// 分片和普通上传使用相同的单文件上限。
 func (s *Service) reserveChunkedUploadQuota(userID string, size int64) (string, error) {
+	return s.reserveUserUploadQuota(userID, size)
+}
+
+func (s *Service) ReserveChunkUploadSession(userID, id string, size int64, expires time.Time, maxSessions int) error {
 	policy, err := s.RuntimePolicy()
 	if err != nil {
-		return "", err
+		return err
 	}
-	return s.reserveUserStoredFileQuota(userID, size, size+1, megabytes(policy.Resource.DailyUploadMB), gigabytes(policy.Resource.StoredFileGB), "")
+	if size <= 0 || size >= megabytes(policy.Resource.ResourceUploadMB) {
+		return BadAuthRequest(fmt.Sprintf("单个上传文件必须小于 %dMB", policy.Resource.ResourceUploadMB))
+	}
+	if !expires.After(time.Now()) || maxSessions <= 0 {
+		return BadAuthRequest("上传会话参数无效")
+	}
+	err = s.repo.ReserveUploadSession(&model.UploadReservation{ID: id, UserID: userID, Size: size, Day: time.Now().UTC().Format("2006-01-02"), ExpiresAt: expires}, megabytes(policy.Resource.DailyUploadMB), gigabytes(policy.Resource.StoredFileGB), maxSessions)
+	return uploadReservationError(err)
+}
+
+func (s *Service) ReleaseChunkUploadSession(userID, id string) error {
+	return s.repo.ReleaseUploadSession(userID, id)
+}
+
+func uploadReservationError(err error) error {
+	if errors.Is(err, repository.ErrUploadSessionLimit) {
+		return NewAppError(429, err.Error())
+	}
+	if errors.Is(err, repository.ErrUploadStorageLimit) || errors.Is(err, repository.ErrDailyUploadLimitExceeded) {
+		return QuotaExceeded(err.Error())
+	}
+	if errors.Is(err, repository.ErrUploadReservationExpired) {
+		return BadAuthRequest(err.Error())
+	}
+	return err
+}
+
+func (s *Service) saveResourceWithinStorageLimit(resource *model.Resource, reservationID string) error {
+	policy, err := s.RuntimePolicy()
+	if err != nil {
+		return err
+	}
+	return uploadReservationError(s.repo.SaveResourceWithinStorageLimit(resource, gigabytes(policy.Resource.StoredFileGB), megabytes(policy.Resource.DailyUploadMB), reservationID))
 }
 
 func (s *Service) reserveGeneratedResourceQuota(userID string, size int64) (string, error) {
diff --git a/backend/internal/database/migrations.go b/backend/internal/database/migrations.go
index 302c7e916..518a27b98 100644
--- a/backend/internal/database/migrations.go
+++ b/backend/internal/database/migrations.go
@@ -146,6 +146,9 @@ var schemaMigrations = []migration{
 	{version: 43, name: "topup_sale_strategies", checksum: "sha256:topup-sale-strategies-v43-20260929", apply: func(tx *gorm.DB) error {
 		return tx.AutoMigrate(&model.TopupProduct{}, &model.PaymentOrder{})
 	}},
+	{version: 45, name: "upload_reservations", checksum: "sha256:upload-reservations-v45-20261005", apply: func(tx *gorm.DB) error {
+		return tx.AutoMigrate(&model.UploadReservation{})
+	}},
 	{version: 46, name: "skill_curation", checksum: "sha256:skill-curation-v46-20261005", apply: migrateSkillCuration},
 	{version: 47, name: "skill_curation_roots", checksum: "sha256:skill-curation-roots-v47-20261005", apply: migrateSkillCurationRoots},
 }
diff --git a/backend/internal/database/migrations_test.go b/backend/internal/database/migrations_test.go
index b96fb150d..ff0d526a7 100644
--- a/backend/internal/database/migrations_test.go
+++ b/backend/internal/database/migrations_test.go
@@ -36,6 +36,9 @@ func TestMigrateSchemaRecordsAndValidatesVersion(t *testing.T) {
 	if !status.Ready || status.Current != CurrentSchemaVersion {
 		t.Fatalf("unexpected schema status: %#v", status)
 	}
+	if !db.Migrator().HasTable(&model.UploadReservation{}) {
+		t.Fatal("upload reservation migration missing")
+	}
 	if !db.Migrator().HasIndex(&schemaMigration{}, "idx_schema_migrations_applied_at") {
 		t.Fatal("schema migration v2 did not create the applied_at index")
 	}
diff --git a/backend/internal/database/schema.go b/backend/internal/database/schema.go
index 0f982a32b..d6f56d39e 100644
--- a/backend/internal/database/schema.go
+++ b/backend/internal/database/schema.go
@@ -17,6 +17,7 @@ import (
 func Models() []any {
 	return []any{
 		&model.CloudAgentExecution{},
+		&model.UploadReservation{},
 		&model.CloudAgentPiSession{},
 		&model.CloudAgentEventRecord{},
 		&model.CloudAgentMessageRecord{},
diff --git a/backend/internal/handler/chunk_quota_security_test.go b/backend/internal/handler/chunk_quota_security_test.go
new file mode 100644
index 000000000..90edba801
--- /dev/null
+++ b/backend/internal/handler/chunk_quota_security_test.go
@@ -0,0 +1,108 @@
+package handler
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+	"infinite-canvas/backend/internal/auth"
+	"infinite-canvas/backend/internal/model"
+	"infinite-canvas/backend/internal/platform"
+	"infinite-canvas/backend/internal/repository"
+	"infinite-canvas/backend/internal/service"
+)
+
+func TestChunkAdmissionReservesBeforeBody(t *testing.T) {
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	sqlDB, _ := db.DB()
+	sqlDB.SetMaxOpenConns(1)
+	t.Cleanup(func() { _ = sqlDB.Close() })
+	if err := db.AutoMigrate(&model.User{}, &model.AuthSession{}, &model.SystemSetting{}, &model.Resource{}, &model.UploadReservation{}, &model.UserDailyUploadUsage{}, &model.StorageLocation{}, &model.UserOSSSetting{}, &model.UserDailyActivity{}); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Create(&model.User{ID: "chunk-user", Username: "chunk-user", Status: model.UserStatusActive}).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Create(&model.AuthSession{ID: "chunk-session", UserID: "chunk-user", TokenHash: auth.HashToken("test-token"), ExpiresAt: time.Now().Add(time.Hour)}).Error; err != nil {
+		t.Fatal(err)
+	}
+	policy := platform.DefaultRuntimePolicy()
+	policy.Resource.ResourceUploadMB = 1
+	data, _ := json.Marshal(policy)
+	if err := db.Create(&model.SystemSetting{Key: "runtime_policy", ValueJSON: string(data)}).Error; err != nil {
+		t.Fatal(err)
+	}
+	repo := repository.New(db)
+	svc := service.New(repo, t.TempDir())
+	previous := runtimeService
+	ConfigureRuntime(svc)
+	t.Cleanup(func() { runtimeService = previous })
+	gin.SetMode(gin.TestMode)
+	router := gin.New()
+	RegisterChunkedUploadRoutes(router.Group("/api"), svc)
+	call := func(method, path, body string) *httptest.ResponseRecorder {
+		req := httptest.NewRequest(method, path, strings.NewReader(body))
+		req.Header.Set("Content-Type", "application/json")
+		req.AddCookie(&http.Cookie{Name: service.SessionCookieName, Value: "chunk-session.test-token"})
+		w := httptest.NewRecorder()
+		router.ServeHTTP(w, req)
+		return w
+	}
+	w := call("POST", "/api/resources/uploads", `{"fileName":"large.txt","size":1048576}`)
+	if w.Code != 400 {
+		t.Fatalf("oversize admission status=%d body=%s", w.Code, w.Body.String())
+	}
+	w = call("POST", "/api/resources/uploads", `{"fileName":"test.txt","size":7}`)
+	if w.Code != 200 {
+		t.Fatalf("admission status=%d body=%s", w.Code, w.Body.String())
+	}
+	var response struct {
+		Data struct {
+			UploadID string `json:"uploadId"`
+		} `json:"data"`
+	}
+	if err := json.Unmarshal(w.Body.Bytes(), &response); err != nil {
+		t.Fatal(err)
+	}
+	id := response.Data.UploadID
+	t.Cleanup(func() {
+		if sess := takeChunkSession(id); sess != nil {
+			sess.mu.Lock()
+			dropChunkSession(id)
+			sess.mu.Unlock()
+		}
+	})
+	if used, _ := repo.DailyUploadBytes("chunk-user", time.Now().UTC().Format("2006-01-02")); used != 7 {
+		t.Fatalf("before first chunk daily bytes=%d want 7", used)
+	}
+	var count int64
+	if err := db.Model(&model.UploadReservation{}).Where("id = ?", id).Count(&count).Error; err != nil || count != 1 {
+		t.Fatalf("admission reservation count=%d err=%v", count, err)
+	}
+	w = call("PUT", fmt.Sprintf("/api/resources/uploads/%s/chunks/0", id), "payload")
+	if w.Code != 200 {
+		t.Fatalf("chunk status=%d body=%s", w.Code, w.Body.String())
+	}
+	w = call("POST", fmt.Sprintf("/api/resources/uploads/%s/complete", id), "")
+	if w.Code != 200 || !bytes.Contains(w.Body.Bytes(), []byte(`"resource"`)) {
+		t.Fatalf("complete status=%d body=%s", w.Code, w.Body.String())
+	}
+	if err := db.Model(&model.UploadReservation{}).Count(&count).Error; err != nil || count != 0 {
+		t.Fatalf("remaining reservations=%d err=%v", count, err)
+	}
+	w = call("POST", fmt.Sprintf("/api/resources/uploads/%s/complete", id), "")
+	if w.Code != 404 {
+		t.Fatalf("duplicate completion status=%d", w.Code)
+	}
+}
diff --git a/backend/internal/handler/resource_upload_session.go b/backend/internal/handler/resource_upload_session.go
index 4e824c64f..5a117b916 100644
--- a/backend/internal/handler/resource_upload_session.go
+++ b/backend/internal/handler/resource_upload_session.go
@@ -5,6 +5,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -18,8 +19,8 @@ import (
 )
 
 // 分片上传会话：把“导入本地媒体”拆成 开始→逐片→合并 三段，单片上限 8MB，
-// 文件整体不再受 multipart 单请求大小限制（对齐 Concat 桌面端“任意大小直接入库”的体验）。
-// 会话状态只存在内存（重启即失效 → 前端整传重试），磁盘暂存在系统临时目录，随会话清理。
+// 整体文件仍遵守资源单文件上限；收片前在数据库预留日额度和存储容量。
+// 分片路由需要粘性路由，内存会话失效后重传；配额预留跨实例共享并按时间到期。
 const (
 	chunkUploadChunkSize   = 8 << 20
 	chunkUploadSlackBytes  = 64 << 10 // MaxBytesReader 允许的超片余量
@@ -29,6 +30,9 @@ const (
 )
 
 type chunkedUploadSession struct {
+	mu             sync.Mutex
+	closed         bool
+	release        func() error
 	ID             string
 	UserID         string
 	FileName       string
@@ -87,9 +91,16 @@ func removeExpiredChunkSessions() {
 	chunkUploadSessions.Lock()
 	defer chunkUploadSessions.Unlock()
 	for id, sess := range chunkUploadSessions.m {
-		if now.Sub(sess.CreatedAt) > chunkUploadTTL {
+		if now.Sub(sess.CreatedAt) > chunkUploadTTL && sess.mu.TryLock() {
+			sess.closed = true
+			if sess.release != nil {
+				if err := sess.release(); err != nil {
+					log.Printf("release expired upload session failed: %v", err)
+				}
+			}
 			_ = os.RemoveAll(sess.Dir)
 			delete(chunkUploadSessions.m, id)
+			sess.mu.Unlock()
 		}
 	}
 }
@@ -105,6 +116,13 @@ func dropChunkSession(id string) {
 	chunkUploadSessions.Lock()
 	defer chunkUploadSessions.Unlock()
 	if sess := chunkUploadSessions.m[id]; sess != nil {
+		// Caller holds sess.mu. Expiry uses TryLock to avoid lock inversion.
+		sess.closed = true
+		if sess.release != nil {
+			if err := sess.release(); err != nil {
+				log.Printf("release upload session failed: %v", err)
+			}
+		}
 		_ = os.RemoveAll(sess.Dir)
 		delete(chunkUploadSessions.m, id)
 	}
@@ -144,31 +162,24 @@ func RegisterChunkedUploadRoutes(r *gin.RouterGroup, svc *service.Service) {
 			fail(c, http.StatusBadRequest, fmt.Errorf("文件大小必须大于 0"))
 			return
 		}
-		// 超账号存储总量的文件无论如何都会失败，提前给出明确提示。
-		if policy.Resource.StoredFileGB > 0 && req.Size > int64(policy.Resource.StoredFileGB)<<30 {
-			fail(c, http.StatusBadRequest, fmt.Errorf("文件超过账号存储总量上限 %dGB", policy.Resource.StoredFileGB))
-			return
-		}
-		// 同一用户并发会话数兜底，防内存占用失控。
-		active := 0
-		chunkUploadSessions.Lock()
-		for _, sess := range chunkUploadSessions.m {
-			if sess.UserID == user.ID {
-				active++
-			}
-		}
-		chunkUploadSessions.Unlock()
-		if active >= chunkUploadMaxPerUser {
-			fail(c, http.StatusTooManyRequests, fmt.Errorf("同时进行中的上传过多，请稍后重试"))
+		removeExpiredChunkSessions()
+		id, createdAt := newUploadSessionID(), time.Now()
+		if err := svc.ReserveChunkUploadSession(user.ID, id, req.Size, createdAt.Add(chunkUploadTTL), chunkUploadMaxPerUser); err != nil {
+			failService(c, err)
 			return
 		}
+		release := func() error { return svc.ReleaseChunkUploadSession(user.ID, id) }
 		dir, err := os.MkdirTemp("", "canvas-chunk-upload-*")
 		if err != nil {
+			if releaseErr := release(); releaseErr != nil {
+				log.Printf("release upload session failed: %v", releaseErr)
+			}
 			failService(c, err)
 			return
 		}
 		session := &chunkedUploadSession{
-			ID:             newUploadSessionID(),
+			ID:             id,
+			release:        release,
 			UserID:         user.ID,
 			FileName:       req.FileName,
 			Kind:           req.Kind,
@@ -179,7 +190,7 @@ func RegisterChunkedUploadRoutes(r *gin.RouterGroup, svc *service.Service) {
 			IdempotencyKey: req.IdempotencyKey,
 			ChunkCount:     int((req.Size + chunkUploadChunkSize - 1) / chunkUploadChunkSize),
 			Dir:            dir,
-			CreatedAt:      time.Now(),
+			CreatedAt:      createdAt,
 		}
 		chunkUploadSessions.Lock()
 		chunkUploadSessions.m[session.ID] = session
@@ -199,6 +210,12 @@ func RegisterChunkedUploadRoutes(r *gin.RouterGroup, svc *service.Service) {
 			return
 		}
 		index, err := strconv.Atoi(c.Param("index"))
+		session.mu.Lock()
+		defer session.mu.Unlock()
+		if session.closed || time.Since(session.CreatedAt) >= chunkUploadTTL {
+			fail(c, http.StatusNotFound, fmt.Errorf("上传会话不存在或已过期，请重新导入"))
+			return
+		}
 		if err != nil || index < 0 || index >= session.ChunkCount {
 			fail(c, http.StatusBadRequest, fmt.Errorf("非法的分片序号"))
 			return
@@ -224,7 +241,7 @@ func RegisterChunkedUploadRoutes(r *gin.RouterGroup, svc *service.Service) {
 			fail(c, http.StatusBadRequest, fmt.Errorf("分片 %d 上传不完整，请重试", index))
 			return
 		}
-		if readErr == nil || extra > 0 {
+		if readErr != io.EOF || extra > 0 {
 			_ = os.Remove(session.chunkPath(index))
 			fail(c, http.StatusBadRequest, fmt.Errorf("分片 %d 超过大小限制", index))
 			return
@@ -245,6 +262,12 @@ func RegisterChunkedUploadRoutes(r *gin.RouterGroup, svc *service.Service) {
 			fail(c, http.StatusNotFound, fmt.Errorf("上传会话不存在或已过期，请重新导入"))
 			return
 		}
+		session.mu.Lock()
+		defer session.mu.Unlock()
+		if session.closed || time.Since(session.CreatedAt) >= chunkUploadTTL {
+			fail(c, http.StatusNotFound, fmt.Errorf("上传会话不存在或已过期，请重新导入"))
+			return
+		}
 		if !session.hasAllChunks() {
 			fail(c, http.StatusBadRequest, fmt.Errorf("上传文件不完整，请重新导入"))
 			return
@@ -287,7 +310,7 @@ func RegisterChunkedUploadRoutes(r *gin.RouterGroup, svc *service.Service) {
 			return
 		}
 		defer fh.Close()
-		resource, svcErr := svc.UploadResourceFile(user.ID, session.FileName, session.Size, session.Kind, session.Width, session.Height, session.DurationMs, fh, session.IdempotencyKey)
+		resource, svcErr := svc.UploadReservedResourceFile(user.ID, session.ID, session.FileName, session.Size, session.Kind, session.Width, session.Height, session.DurationMs, fh, session.IdempotencyKey)
 		// 无论成败都结束会话：失败时前端会整传重试，不需要保留残片。
 		dropChunkSession(id)
 		if svcErr != nil {
diff --git a/backend/internal/model/upload_reservation.go b/backend/internal/model/upload_reservation.go
new file mode 100644
index 000000000..5b1d8db20
--- /dev/null
+++ b/backend/internal/model/upload_reservation.go
@@ -0,0 +1,13 @@
+package model
+
+import "time"
+
+// UploadReservation survives process restarts; expiry, not process ownership,
+// bounds its lifetime. Day records the UTC quota bucket charged at admission.
+type UploadReservation struct {
+	ID        string    `gorm:"primaryKey;size:64"`
+	UserID    string    `gorm:"index;size:64;not null"`
+	Size      int64     `gorm:"not null"`
+	Day       string    `gorm:"size:10;not null"`
+	ExpiresAt time.Time `gorm:"index;not null"`
+}
diff --git a/backend/internal/repository/upload_reservations.go b/backend/internal/repository/upload_reservations.go
new file mode 100644
index 000000000..43f27efa2
--- /dev/null
+++ b/backend/internal/repository/upload_reservations.go
@@ -0,0 +1,141 @@
+package repository
+
+import (
+	"errors"
+	"time"
+
+	"gorm.io/gorm"
+	"infinite-canvas/backend/internal/model"
+)
+
+var ErrUploadStorageLimit = errors.New("账号存储容量不足")
+var ErrUploadSessionLimit = errors.New("同时进行中的上传过多，请稍后重试")
+var ErrUploadReservationExpired = errors.New("上传会话不存在或已过期，请重新导入")
+
+func lockUploadStorage(tx *gorm.DB, userID string) error {
+	switch tx.Dialector.Name() {
+	case "postgres":
+		return tx.Exec("SELECT pg_advisory_xact_lock(hashtext(?)::bigint)", "upload-storage:"+userID).Error
+	case "sqlite":
+		return tx.Exec("UPDATE upload_reservations SET size = size WHERE 1 = 0").Error
+	default:
+		return gorm.ErrInvalidData
+	}
+}
+
+func (r *Repository) ReserveUploadSession(reservation *model.UploadReservation, dailyLimit, storedLimit int64, sessionLimit int) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		if err := lockUploadStorage(tx, reservation.UserID); err != nil {
+			return err
+		}
+		repo := New(tx)
+		now := time.Now()
+		if !reservation.ExpiresAt.After(now) {
+			return ErrUploadReservationExpired
+		}
+		reservation.Day = now.UTC().Format("2006-01-02")
+		var expired []model.UploadReservation
+		if err := tx.Where("user_id = ? AND expires_at <= ?", reservation.UserID, now).Find(&expired).Error; err != nil {
+			return err
+		}
+		for _, old := range expired {
+			if err := repo.ReleaseDailyUpload(old.UserID, old.Day, old.Size); err != nil {
+				return err
+			}
+			if err := tx.Delete(&old).Error; err != nil {
+				return err
+			}
+		}
+		var active int64
+		if err := tx.Model(&model.UploadReservation{}).Where("user_id = ?", reservation.UserID).Count(&active).Error; err != nil {
+			return err
+		}
+		if active >= int64(sessionLimit) {
+			return ErrUploadSessionLimit
+		}
+		stored, err := repo.UserStoredFileBytes(reservation.UserID)
+		if err != nil {
+			return err
+		}
+		var pending int64
+		if err := tx.Model(&model.UploadReservation{}).Select("COALESCE(SUM(size),0)").Where("user_id = ?", reservation.UserID).Scan(&pending).Error; err != nil {
+			return err
+		}
+		if reservation.Size <= 0 || stored >= storedLimit || pending >= storedLimit-stored || reservation.Size >= storedLimit-stored-pending {
+			return ErrUploadStorageLimit
+		}
+		if err := repo.ReserveDailyUpload(reservation.UserID, reservation.Day, reservation.Size, dailyLimit); err != nil {
+			return err
+		}
+		return tx.Create(reservation).Error
+	})
+}
+
+func (r *Repository) ReleaseUploadSession(userID, id string) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		if err := lockUploadStorage(tx, userID); err != nil {
+			return err
+		}
+		var reservation model.UploadReservation
+		if err := tx.Where("id = ? AND user_id = ?", id, userID).First(&reservation).Error; err != nil {
+			if errors.Is(err, gorm.ErrRecordNotFound) {
+				return nil
+			}
+			return err
+		}
+		if err := New(tx).ReleaseDailyUpload(userID, reservation.Day, reservation.Size); err != nil {
+			return err
+		}
+		return tx.Delete(&reservation).Error
+	})
+}
+
+// SaveResourceWithinStorageLimit publishes ready bytes and consumes the session
+// reservation under the same database lock used by admission on every instance.
+func (r *Repository) SaveResourceWithinStorageLimit(resource *model.Resource, limit, dailyLimit int64, reservationID string) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		if err := lockUploadStorage(tx, resource.UserID); err != nil {
+			return err
+		}
+		now := time.Now()
+		if reservationID != "" {
+			var reservation model.UploadReservation
+			if err := tx.Where("id = ? AND user_id = ? AND size = ? AND expires_at > ?", reservationID, resource.UserID, resource.Size, now).First(&reservation).Error; err != nil {
+				if errors.Is(err, gorm.ErrRecordNotFound) {
+					return ErrUploadReservationExpired
+				}
+				return err
+			}
+			day := now.UTC().Format("2006-01-02")
+			if reservation.Day != day {
+				repo := New(tx)
+				if err := repo.ReserveDailyUpload(resource.UserID, day, reservation.Size, dailyLimit); err != nil {
+					return err
+				}
+				if err := repo.ReleaseDailyUpload(resource.UserID, reservation.Day, reservation.Size); err != nil {
+					return err
+				}
+			}
+		}
+		// Save inside the transaction so physical-object deduplication uses the
+		// existing usage query; rollback leaves the resource non-ready on denial.
+		if err := tx.Save(resource).Error; err != nil {
+			return err
+		}
+		stored, err := New(tx).UserStoredFileBytes(resource.UserID)
+		if err != nil {
+			return err
+		}
+		var pending int64
+		if err := tx.Model(&model.UploadReservation{}).Select("COALESCE(SUM(size),0)").Where("user_id = ? AND id <> ? AND expires_at > ?", resource.UserID, reservationID, now).Scan(&pending).Error; err != nil {
+			return err
+		}
+		if stored >= limit || pending >= limit-stored {
+			return ErrUploadStorageLimit
+		}
+		if reservationID != "" {
+			return tx.Delete(&model.UploadReservation{}, "id = ? AND user_id = ?", reservationID, resource.UserID).Error
+		}
+		return nil
+	})
+}
diff --git a/backend/internal/repository/upload_reservations_test.go b/backend/internal/repository/upload_reservations_test.go
new file mode 100644
index 000000000..507992b5b
--- /dev/null
+++ b/backend/internal/repository/upload_reservations_test.go
@@ -0,0 +1,195 @@
+package repository
+
+import (
+	"errors"
+	"fmt"
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+	"infinite-canvas/backend/internal/model"
+)
+
+func uploadReservationTestDB(t *testing.T) (*gorm.DB, *Repository, *Repository) {
+	t.Helper()
+	dsn := filepath.Join(t.TempDir(), "uploads.db") + "?_busy_timeout=5000&_journal_mode=WAL"
+	db, err := gorm.Open(sqlite.Open(dsn), &gorm.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := db.AutoMigrate(&model.UploadReservation{}, &model.UserDailyUploadUsage{}, &model.Resource{}); err != nil {
+		t.Fatal(err)
+	}
+	peer, err := gorm.Open(sqlite.Open(dsn), &gorm.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, conn := range []*gorm.DB{db, peer} {
+		sqlDB, _ := conn.DB()
+		t.Cleanup(func() { _ = sqlDB.Close() })
+	}
+	return db, New(db), New(peer)
+}
+
+func TestUploadReservationConcurrentAdmission(t *testing.T) {
+	for _, tc := range []struct {
+		name                     string
+		size, daily, stored      int64
+		sessions, attempts, want int
+		denied                   error
+	}{
+		{"sessions", 1, 1000, 1000, 32, 40, 32, ErrUploadSessionLimit},
+		{"storage", 60, 1000, 100, 32, 2, 1, ErrUploadStorageLimit},
+		{"daily", 60, 100, 1000, 32, 2, 1, ErrDailyUploadLimitExceeded},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			_, first, second := uploadReservationTestDB(t)
+			start := make(chan struct{})
+			results := make(chan error, tc.attempts)
+			var wg sync.WaitGroup
+			for i := 0; i < tc.attempts; i++ {
+				wg.Add(1)
+				go func() {
+					defer wg.Done()
+					<-start
+					repo := []*Repository{first, second}[i%2]
+					results <- repo.ReserveUploadSession(&model.UploadReservation{ID: fmt.Sprint(i), UserID: "user", Size: tc.size, ExpiresAt: time.Now().Add(time.Hour)}, tc.daily, tc.stored, tc.sessions)
+				}()
+			}
+			close(start)
+			wg.Wait()
+			close(results)
+			accepted := 0
+			for err := range results {
+				if err == nil {
+					accepted++
+				} else if !errors.Is(err, tc.denied) {
+					t.Fatalf("unexpected denial: %v", err)
+				}
+			}
+			if accepted != tc.want {
+				t.Fatalf("accepted=%d want=%d", accepted, tc.want)
+			}
+			if used, err := first.DailyUploadBytes("user", time.Now().UTC().Format("2006-01-02")); err != nil || used != int64(tc.want)*tc.size {
+				t.Fatalf("reserved bytes=%d err=%v", used, err)
+			}
+		})
+	}
+}
+
+func TestUploadReservationAtomicCapacityCommit(t *testing.T) {
+	db, first, second := uploadReservationTestDB(t)
+	start := make(chan struct{})
+	results := make(chan error, 2)
+	var wg sync.WaitGroup
+	for i, repo := range []*Repository{first, second} {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			<-start
+			results <- repo.SaveResourceWithinStorageLimit(&model.Resource{ID: fmt.Sprint(i), UserID: "user", ObjectKey: fmt.Sprint(i), Status: model.ResourceStatusReady, Size: 60}, 100, 1000, "")
+		}()
+	}
+	close(start)
+	wg.Wait()
+	close(results)
+	accepted := 0
+	for err := range results {
+		if err == nil {
+			accepted++
+		} else if !errors.Is(err, ErrUploadStorageLimit) {
+			t.Fatal(err)
+		}
+	}
+	if accepted != 1 {
+		t.Fatalf("committed=%d want=1", accepted)
+	}
+	var count int64
+	if err := db.Model(&model.Resource{}).Count(&count).Error; err != nil || count != 1 {
+		t.Fatalf("resource rows=%d err=%v", count, err)
+	}
+}
+
+func TestUploadReservationCommitAndExpiry(t *testing.T) {
+	db, r, peer := uploadReservationTestDB(t)
+	old := model.UploadReservation{ID: "old", UserID: "user", Size: 60, Day: "2026-10-04", ExpiresAt: time.Now().Add(-time.Hour)}
+	if err := db.Create(&old).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := r.ReserveDailyUpload("user", old.Day, 60, 1000); err != nil {
+		t.Fatal(err)
+	}
+	lease := model.UploadReservation{ID: "new", UserID: "user", Size: 60, Day: "2026-10-05", ExpiresAt: time.Now().Add(time.Hour)}
+	if err := peer.ReserveUploadSession(&lease, 1000, 100, 1); err != nil {
+		t.Fatal(err)
+	}
+	if used, _ := r.DailyUploadBytes("user", old.Day); used != 0 {
+		t.Fatalf("expired previous-day bytes=%d", used)
+	}
+	if err := r.ReleaseUploadSession("other", lease.ID); err != nil {
+		t.Fatal(err)
+	}
+	other := model.Resource{ID: "other", UserID: "user", Size: 40, Status: model.ResourceStatusReady, ObjectKey: "other"}
+	if err := r.SaveResourceWithinStorageLimit(&other, 100, 1000, ""); !errors.Is(err, ErrUploadStorageLimit) {
+		t.Fatalf("ordinary upload ignored reserved capacity: %v", err)
+	}
+	resource := model.Resource{ID: "resource", UserID: "user", Size: 59, Status: model.ResourceStatusReady, ObjectKey: "resource"}
+	if err := r.SaveResourceWithinStorageLimit(&resource, 100, 1000, lease.ID); !errors.Is(err, ErrUploadReservationExpired) {
+		t.Fatalf("mismatched lease: %v", err)
+	}
+	resource.Size = 60
+	if err := r.SaveResourceWithinStorageLimit(&resource, 100, 1000, lease.ID); err != nil {
+		t.Fatal(err)
+	}
+	if err := peer.ReleaseUploadSession("user", lease.ID); err != nil {
+		t.Fatal(err)
+	}
+	if used, _ := r.DailyUploadBytes("user", lease.Day); used != 60 {
+		t.Fatalf("committed daily bytes=%d", used)
+	}
+	if err := r.SaveResourceWithinStorageLimit(&resource, 100, 1000, lease.ID); !errors.Is(err, ErrUploadReservationExpired) {
+		t.Fatalf("lease reused: %v", err)
+	}
+	resource.ID = "expired"
+	if err := r.SaveResourceWithinStorageLimit(&resource, 100, 1000, old.ID); !errors.Is(err, ErrUploadReservationExpired) {
+		t.Fatalf("expired lease accepted: %v", err)
+	}
+}
+
+func TestUploadReservationCommitAcrossUTCDay(t *testing.T) {
+	db, r, _ := uploadReservationTestDB(t)
+	today := time.Now().UTC().Format("2006-01-02")
+	yesterday := time.Now().UTC().Add(-24 * time.Hour).Format("2006-01-02")
+	lease := model.UploadReservation{ID: "midnight", UserID: "user", Size: 15, Day: yesterday, ExpiresAt: time.Now().Add(time.Hour)}
+	if err := db.Create(&lease).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := r.ReserveDailyUpload("user", yesterday, 15, 100); err != nil {
+		t.Fatal(err)
+	}
+	if err := r.ReserveDailyUpload("user", today, 90, 100); err != nil {
+		t.Fatal(err)
+	}
+	resource := model.Resource{ID: "midnight", UserID: "user", Size: 15, ObjectKey: "midnight", Status: model.ResourceStatusReady}
+	if err := r.SaveResourceWithinStorageLimit(&resource, 1000, 100, lease.ID); !errors.Is(err, ErrDailyUploadLimitExceeded) {
+		t.Fatalf("new-day quota bypassed: %v", err)
+	}
+	if used, _ := r.DailyUploadBytes("user", yesterday); used != 15 {
+		t.Fatalf("failed commit refunded reservation: %d", used)
+	}
+	if err := r.ReleaseDailyUpload("user", today, 90); err != nil {
+		t.Fatal(err)
+	}
+	if err := r.SaveResourceWithinStorageLimit(&resource, 1000, 100, lease.ID); err != nil {
+		t.Fatal(err)
+	}
+	if used, _ := r.DailyUploadBytes("user", today); used != 15 {
+		t.Fatalf("new-day usage=%d", used)
+	}
+	if used, _ := r.DailyUploadBytes("user", yesterday); used != 0 {
+		t.Fatalf("old-day reservation=%d", used)
+	}
+}
diff --git a/docs/content/docs/backend/backend-database.mdx b/docs/content/docs/backend/backend-database.mdx
index 9874dcaa6..4211cb0e6 100644
--- a/docs/content/docs/backend/backend-database.mdx
+++ b/docs/content/docs/backend/backend-database.mdx
@@ -5,6 +5,14 @@ description: 影策后端核心持久化表与状态边界
 
 # 后端数据库
 
+## 分片上传预留
+
+Schema 45 新增 `upload_reservations`：`id`、`user_id`、`size`、`day`、`expires_at`。创建会话时在数据库事务内检查并行会话数、现有资源容量、未到期预留和每日上传用量，更新既有 `user_daily_upload_usages` 后插入预留。SQLite 先取得写锁，PostgreSQL 使用账号级事务 advisory lock。
+
+资源变为 ready 与删除对应预留在同一事务中提交；普通资源上传及生成结果的容量提交也使用同一锁，并计入分片预留。沿用 `UserStoredFileBytes` 的 ready 物理对象去重口径，不改变容量配置。跨 UTC 日期完成时重新预留当天日额度并释放原日额度，失败则整体回滚。
+
+预留有效期 90 分钟。失败或会话删除时释放原日额度；再次创建该账号会话时清理已到期预留。进程重启不批量删除其他实例的预留。分片文件与路由会话仍在本机，需要粘性路由；崩溃后的残片需要部署侧临时目录清理策略，未增加跨实例文件恢复或启动时全局清扫。
+
 ## 更新公告配置
 
 外观 JSON 合同版本 10 新增 `updates`：`enabled`、`currentVersion`、`releases`。每个版本保存 `id/version/title/date/blocks`，内容块保存 `id/type/text/resourceId/caption/layout`；公共媒体 URL 由服务端按当前引用生成，不保存客户端 URL。关闭开关保留公告和资源引用，只关闭公共展示。不增加数据库表或 schema 迁移。
diff --git a/docs/content/docs/backend/http-api.mdx b/docs/content/docs/backend/http-api.mdx
index 92f232c7d..ea1397648 100644
--- a/docs/content/docs/backend/http-api.mdx
+++ b/docs/content/docs/backend/http-api.mdx
@@ -11,6 +11,12 @@ description: 信封、错误码与 OpenAPI
 
 邮箱原值仍按原有小写、去首尾空格规则保存。登录、密码重置、验证码收件地址保持精确邮箱匹配，避免既有重复别名账号被合并或错误授权。已存在的重复账号不迁移、不删除、不重新发放注册奖励；它们会阻止相同规范信箱的新注册。写入前在事务内重新检查，以覆盖不同实例使用不同验证码的并发注册。无数据库结构迁移；唯一性由公开注册与绑定的事务入口保证，直接 SQL 写入不属于该约束入口。
 
+## 分片上传配额
+
+`POST /resources/uploads` 在接收分片前预留整个文件的日额度和账号容量。文件大小必须严格小于 `resourceUploadMB`；同一账号最多 32 个未到期会话，跨后端实例共同计数。未满足配额的请求不会创建分片目录。分片和完成请求按会话串行执行；会话过期或已完成返回 404，重新创建会话后可整传重试。
+
+完成上传时以数据库事务提交容量并消费预留，使用既有资源幂等标识。失败释放预留；跨 UTC 日期完成需要通过当天日额度检查。请求与响应字段不变。
+
 ## AutoDL 视频画面规格配置
 
 渠道模型的 `capabilityConfig.video.resolutions` 与 `defaultResolution` 直接表示所选完整分辨率与默认值，始终生效；不再使用或返回 `customSizeEnabled`、`customScreenSpec`。AutoDL v2.3.0 未声明独立比例参数，因此 `ratios` 为空、`defaultRatio` 为空字符串，横竖与方形由完整分辨率标签表达。