feat(panel): let a sponsor slot start at a scheduled time

sponsors.json only had an end date, so a booked placement had to be
added to the file on the day it started. An optional `from` now hides
a sponsor (and its logo) until that instant; entries without it show
immediately as before.

internal/amneziawgnet/bench_test.go

@@ -31,8 +31,8 @@ func BenchmarkStackTunWrite(b *testing.B) {
 
 	b.SetBytes(int64(len(packet)))
 	b.ReportAllocs()
-	b.ResetTimer()
-	for range b.N {
+
+	for b.Loop() {
 		if _, err := tun.Write(bufs, 0); err != nil {
 			b.Fatalf("Write: %v", err)
 		}
@@ -49,8 +49,8 @@ func BenchmarkStackTunRead(b *testing.B) {
 
 	b.SetBytes(int64(len(packet)))
 	b.ReportAllocs()
-	b.ResetTimer()
-	for range b.N {
+
+	for b.Loop() {
 		tun.incomingPacket <- buffer.NewViewWithData(packet)
 		if _, err := tun.Read(buf, sizes, 0); err != nil {
 			b.Fatalf("Read: %v", err)
@@ -77,8 +77,8 @@ func BenchmarkUDPDatagramDelivery(b *testing.B) {
 
 	b.SetBytes(int64(len(payload)))
 	b.ReportAllocs()
-	b.ResetTimer()
-	for range b.N {
+
+	for b.Loop() {
 		if _, err := st.Write(bufs, 0); err != nil {
 			b.Fatalf("Write: %v", err)
 		}

internal/web/service/panel/sponsor.go

@@ -26,6 +26,7 @@ type Sponsor struct {
 	Name   string            `json:"name" example:"Acme VPS"`
 	Enable *bool             `json:"enable,omitempty" example:"true"`
 	Slots  []string          `json:"slots"`
+	From   *time.Time        `json:"from,omitempty" example:"2026-10-01T00:00:00Z"`
 	Until  time.Time         `json:"until" example:"2026-11-01T00:00:00Z"`
 	Logo   string            `json:"logo,omitempty" example:"/sponsors/logo/acme.png"`
 	Title  map[string]string `json:"title"`
@@ -77,8 +78,8 @@ var (
 	logos   = map[string]sponsorLogo{}
 )
 
-// GetSponsors returns the currently active sponsors. The remote file is cached,
-// but expiry is re-checked on every call so a slot ends exactly at Until.
+// GetSponsors returns the currently active sponsors. The remote file is cached, but the
+// window is re-checked on every call so a slot starts exactly at From and ends at Until.
 func (s *PanelService) GetSponsors() (*SponsorList, error) {
 	raw, err := cachedSponsors()
 	if err != nil {
@@ -220,7 +221,8 @@ func activeSponsors(raw *SponsorList, now time.Time) *SponsorList {
 	for _, sp := range raw.Sponsors {
 		// A missing enable counts as on, so a forgotten field never hides a paid slot.
 		disabled := sp.Enable != nil && !*sp.Enable
-		if disabled || sp.ID == "" || !now.Before(sp.Until) || !strings.HasPrefix(sp.Link, "https://") {
+		notStarted := sp.From != nil && now.Before(*sp.From)
+		if disabled || notStarted || sp.ID == "" || !now.Before(sp.Until) || !strings.HasPrefix(sp.Link, "https://") {
 			continue
 		}
 		// A bad logo name drops only the logo; the paid slot still renders with its initial.

internal/web/service/panel/sponsor_test.go

@@ -37,6 +37,8 @@ func TestActiveSponsorsFilters(t *testing.T) {
 	}{
 		{"valid", func(*Sponsor) {}, true},
 		{"expired", func(s *Sponsor) { s.Until = sponsorTestNow }, false},
+		{"not started yet", func(s *Sponsor) { s.From = new(sponsorTestNow.Add(time.Hour)) }, false},
+		{"starts exactly now", func(s *Sponsor) { s.From = new(sponsorTestNow) }, true},
 		{"enable false with future until", func(s *Sponsor) { s.Enable = new(false) }, false},
 		{"enable true without until", func(s *Sponsor) { s.Enable, s.Until = new(true), time.Time{} }, false},
 		{"enable true with future until", func(s *Sponsor) { s.Enable = new(true) }, true},