feat: email admin when MokoGitea update is detected

The update checker now emails the first admin user when a new version
is found on the configured channel. Notifications are deduplicated —
only sent once per new version, not on every cron tick.

- Added NotifyFunc callback in updatechecker module
- Wired to mailer in cron task registration
- Created mail_update.go with plain-text email including version,
  channel, release URL, and docker pull command

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/updatechecker/updatechecker.go

@@ -26,9 +26,14 @@ type UpdateInfo struct {
 	CheckedAt       time.Time
 }
 
+// NotifyFunc is called when a new update is detected for the first time.
+// Set this from the cron/mailer layer to send admin email notifications.
+var NotifyFunc func(info *UpdateInfo)
+
 var (
-	cachedInfo *UpdateInfo
-	mu         sync.RWMutex
+	cachedInfo        *UpdateInfo
+	lastNotifiedVer   string
+	mu                sync.RWMutex
 )
 
 // xmlUpdates mirrors the updates.xml structure (Joomla-style).
@@ -134,16 +139,22 @@ func CheckForUpdate() error {
 	}
 
 	// Update is available if the latest version string is not a prefix of the current version.
-	// e.g., current "1.26.1+305-gabcdef" does not start with "04.00.00"
-	// This handles both moko semver and git-describe suffixed versions.
 	info.UpdateAvailable = latestVersion != "" && !strings.Contains(currentVersion, latestVersion)
 
 	mu.Lock()
 	cachedInfo = info
+	// Notify only once per new version (avoid spamming on every cron tick)
+	shouldNotify := info.UpdateAvailable && latestVersion != lastNotifiedVer
+	if shouldNotify {
+		lastNotifiedVer = latestVersion
+	}
 	mu.Unlock()
 
 	if info.UpdateAvailable {
 		log.Info("MokoGitea update available: %s [%s] (current: %s)", latestVersion, channel, currentVersion)
+		if shouldNotify && NotifyFunc != nil {
+			NotifyFunc(info)
+		}
 	} else {
 		log.Debug("MokoGitea is up to date: %s [%s]", currentVersion, channel)
 	}

services/cron/tasks_basic.go

@@ -15,6 +15,7 @@ import (
 	"git.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/setting"
 	"git.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/updatechecker"
 	"git.mokoconsulting.tech/MokoConsulting/MokoGitea/services/auth"
+	"git.mokoconsulting.tech/MokoConsulting/MokoGitea/services/mailer"
 	"git.mokoconsulting.tech/MokoConsulting/MokoGitea/services/migrations"
 	mirror_service "git.mokoconsulting.tech/MokoConsulting/MokoGitea/services/mirror"
 	packages_cleanup_service "git.mokoconsulting.tech/MokoConsulting/MokoGitea/services/packages/cleanup"
@@ -190,6 +191,11 @@ func initBasicTasks() {
 }
 
 func registerUpdateChecker() {
+	// Wire up email notification for admin when updates are detected
+	updatechecker.NotifyFunc = func(info *updatechecker.UpdateInfo) {
+		mailer.SendUpdateNotification(info.LatestVersion, info.Channel, info.ReleaseURL, info.DockerImage)
+	}
+
 	RegisterTaskFatal("update_checker", &BaseConfig{
 		Enabled:    true,
 		RunAtStart: true,

services/mailer/mail_update.go

@@ -0,0 +1,53 @@
+// Copyright 2026 Moko Consulting <hello@mokoconsulting.tech>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package mailer
+
+import (
+	"context"
+	"fmt"
+
+	user_model "git.mokoconsulting.tech/MokoConsulting/MokoGitea/models/user"
+	"git.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/log"
+	"git.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/setting"
+	sender_service "git.mokoconsulting.tech/MokoConsulting/MokoGitea/services/mailer/sender"
+)
+
+// SendUpdateNotification emails all admin users when a new MokoGitea version is available.
+func SendUpdateNotification(version, channel, releaseURL, dockerImage string) {
+	if setting.MailService == nil {
+		log.Debug("Update notification skipped: mail service not configured")
+		return
+	}
+
+	admin, err := user_model.GetAdminUser(context.Background())
+	if err != nil {
+		log.Error("SendUpdateNotification: GetAdminUser: %v", err)
+		return
+	}
+
+	subject := fmt.Sprintf("[MokoGitea] Update available: %s (%s)", version, channel)
+
+	body := fmt.Sprintf(`MokoGitea Update Available
+
+A new version is available on the %s channel.
+
+Version:  %s
+Channel:  %s
+Current:  %s`, channel, version, channel, setting.AppVer)
+
+	if releaseURL != "" {
+		body += fmt.Sprintf("\nRelease:  %s", releaseURL)
+	}
+	if dockerImage != "" {
+		body += fmt.Sprintf("\nDocker:   docker pull %s", dockerImage)
+	}
+
+	body += fmt.Sprintf("\n\nUpdate the channel in Site Administration > Dashboard.\n\n— %s", setting.AppName)
+
+	msg := sender_service.NewMessage(admin.EmailTo(), subject, body)
+	msg.Info = "Update notification"
+
+	SendAsync(msg)
+	log.Info("Update notification sent to %s for version %s [%s]", admin.Email, version, channel)
+}