fix(update): detach in-place update from the HTTP request lifetime

The in-place update ran entirely inside c.Request.Context(). Browsers and
reverse proxies commonly abort long-idle requests (axios global timeout
30s, nginx proxy_read_timeout 60s by default), which canceled the request
context mid-download and killed every slow update with
'download failed: context canceled' while the version stayed unchanged.
Users behind slow GitHub links saw the update button fail at a wall-clock
ceiling (~60s) on every attempt (#4504).

- Run PerformUpdate and RollbackToVersion on a context detached from the
  request (context.WithoutCancel) and bounded by a 15-minute deadline so
  the 10-minute GitHub download client owns its own timeout. A client
  disconnect no longer aborts the binary swap; retries then hit the
  system operation lock or report 'Already up to date'.
- Raise the frontend timeout for the update/rollback calls from the
  global 30s axios default to 15 minutes so the browser can actually
  wait for the result.

Fixes #4504

backend/internal/handler/admin/system_handler.go

@@ -22,6 +22,27 @@ type SystemHandler struct {
 	lockSvc   *service.SystemOperationLockService
 }
 
+// systemUpdateTimeout bounds a full in-place update or rollback: the release
+// manifest fetch plus a large binary download over slow links. It must stay
+// above the GitHub download client timeout (10 minutes) so the download owns
+// its own deadline.
+const systemUpdateTimeout = 15 * time.Minute
+
+// systemUpdateContext detaches a long-running update/rollback from the HTTP
+// request lifetime. Browsers and reverse proxies commonly abort idle requests
+// after 30-60s (axios default, nginx proxy_read_timeout), which canceled
+// c.Request.Context() mid-download and killed the update with
+// "download failed: context canceled" (#4504). The swap keeps running after a
+// client disconnect; a later retry then hits the system operation lock or
+// reports "Already up to date".
+func systemUpdateContext(ctx context.Context) (context.Context, context.CancelFunc) {
+	base := context.Background()
+	if ctx != nil {
+		base = context.WithoutCancel(ctx)
+	}
+	return context.WithTimeout(base, systemUpdateTimeout)
+}
+
 type systemUpdateService interface {
 	CheckUpdate(ctx context.Context, force bool) (*service.UpdateInfo, error)
 	PerformUpdate(ctx context.Context) error
@@ -75,9 +96,12 @@ func (h *SystemHandler) PerformUpdate(c *gin.Context) {
 			release(releaseReason, succeeded)
 		}()
 
-		if err := h.updateSvc.PerformUpdate(ctx); err != nil {
+		updateCtx, cancel := systemUpdateContext(ctx)
+		defer cancel()
+
+		if err := h.updateSvc.PerformUpdate(updateCtx); err != nil {
 			if errors.Is(err, service.ErrNoUpdateAvailable) {
-				info, checkErr := h.updateSvc.CheckUpdate(ctx, false)
+				info, checkErr := h.updateSvc.CheckUpdate(updateCtx, false)
 				if checkErr != nil {
 					releaseReason = "SYSTEM_UPDATE_FAILED"
 					return nil, checkErr
@@ -152,7 +176,10 @@ func (h *SystemHandler) Rollback(c *gin.Context) {
 		}()
 
 		if targetVersion != "" {
-			err = h.updateSvc.RollbackToVersion(ctx, targetVersion)
+			// 指定版本回退同样要下载完整二进制，与更新一样和请求生命周期解耦。
+			rollbackCtx, cancel := systemUpdateContext(ctx)
+			defer cancel()
+			err = h.updateSvc.RollbackToVersion(rollbackCtx, targetVersion)
 		} else {
 			err = h.updateSvc.Rollback()
 		}