feat: add resilient container restart controls

internal/web/static/app.js

@@ -478,6 +478,115 @@
     });
   }
 
+  const containerRestartForm = document.querySelector('[data-container-restart-form]');
+  if (containerRestartForm) {
+    const overlay = document.querySelector('[data-container-restart-overlay]');
+    const title = overlay?.querySelector('[data-container-restart-title]');
+    const message = overlay?.querySelector('[data-container-restart-message]');
+    const close = overlay?.querySelector('[data-container-restart-close]');
+    const submit = containerRestartForm.querySelector('button[type="submit"]');
+    let polling = false;
+    let startedAt = 0;
+    let expectedInstance = containerRestartForm.dataset.instanceId || '';
+    let consecutiveReady = 0;
+    let sawUnavailable = false;
+
+    const setRestartState = (state, heading, text) => {
+      if (!overlay) return;
+      overlay.dataset.updateState = state;
+      overlay.setAttribute('aria-busy', String(state !== 'complete' && state !== 'failed'));
+      if (title) title.textContent = heading;
+      if (message) message.textContent = text;
+    };
+
+    const pollContainerRestart = async () => {
+      if (!polling) return;
+      if (Date.now() - startedAt > 90 * 1000) {
+        polling = false;
+        setRestartState('failed', 'Neustart nicht bestätigt', 'Die neue Container-Instanz wurde nicht rechtzeitig erreichbar. Prüfe den Containerstatus am Docker-Host.');
+        if (close) close.hidden = false;
+        return;
+      }
+      try {
+        const response = await fetch(`/healthz?restart-check=${Date.now()}`, {cache: 'no-store', credentials: 'same-origin'});
+        if (!response.ok) throw new Error('healthcheck unavailable');
+        const currentInstance = response.headers.get('X-Domain-Control-Instance') || '';
+        const isNewInstance = expectedInstance
+          ? (currentInstance !== '' && currentInstance !== expectedInstance) || (currentInstance === '' && sawUnavailable)
+          : sawUnavailable;
+        if (isNewInstance) {
+          consecutiveReady += 1;
+          setRestartState('restarting', 'Neue Instanz wird geprüft', 'Der Container ist wieder erreichbar. Die Verbindung wird noch einmal bestätigt.');
+          if (consecutiveReady >= 2) {
+            polling = false;
+            setRestartState('complete', 'Container neu gestartet', 'Die neue Container-Instanz ist bereit. Die Seite wird neu geladen.');
+            window.setTimeout(() => window.location.assign('/system'), 900);
+            return;
+          }
+        } else {
+          consecutiveReady = 0;
+          setRestartState('restarting', 'Container wird neu gestartet', 'Die bisherige Instanz wird geordnet beendet.');
+        }
+      } catch {
+        sawUnavailable = true;
+        consecutiveReady = 0;
+        setRestartState('restarting', 'Verbindung wird aufgebaut', 'Der Container ist kurz nicht erreichbar und startet automatisch neu.');
+      }
+      window.setTimeout(pollContainerRestart, 700);
+    };
+
+    containerRestartForm.addEventListener('submit', async (event) => {
+      event.preventDefault();
+      if (polling || !overlay) return;
+      if (!window.confirm('Den vollständigen DynDNS-Container jetzt neu starten? Der Dienst ist kurz nicht erreichbar.')) return;
+
+      const formData = new FormData(containerRestartForm);
+      const requestBody = new URLSearchParams();
+      for (const [name, value] of formData) {
+        if (typeof value === 'string') requestBody.append(name, value);
+      }
+      polling = true;
+      startedAt = Date.now();
+      consecutiveReady = 0;
+      sawUnavailable = false;
+      overlay.hidden = false;
+      if (close) close.hidden = true;
+      if (submit) submit.disabled = true;
+      document.body.classList.add('software-update-open');
+      setRestartState('restarting', 'Neustart wird vorbereitet', 'Die Anwendung wird geordnet beendet und automatisch wieder gestartet.');
+
+      let responseReceived = false;
+      try {
+        const response = await fetch(containerRestartForm.action, {method: 'POST', body: requestBody, headers: {'Accept': 'application/json'}, credentials: 'same-origin'});
+        responseReceived = true;
+        const contentType = response.headers.get('content-type') || '';
+        const result = contentType.includes('application/json')
+          ? await response.json().catch(() => ({}))
+          : {message: (await response.text()).trim().slice(0, 240)};
+        if (!response.ok || !result.accepted) throw new Error(result.message || 'Container-Neustart konnte nicht gestartet werden.');
+        expectedInstance = result.instance_id || expectedInstance;
+      } catch (error) {
+        if (responseReceived) {
+          polling = false;
+          setRestartState('failed', 'Neustart nicht gestartet', error instanceof Error ? error.message : 'Container-Neustart konnte nicht gestartet werden.');
+          if (close) close.hidden = false;
+          if (submit) submit.disabled = false;
+          return;
+        }
+        sawUnavailable = true;
+      }
+      window.setTimeout(pollContainerRestart, 350);
+    });
+
+    close?.addEventListener('click', () => {
+      polling = false;
+      overlay.hidden = true;
+      close.hidden = true;
+      document.body.classList.remove('software-update-open');
+      if (submit) submit.disabled = false;
+    });
+  }
+
   const countdowns = [...document.querySelectorAll('[data-countdown]')];
   const currentIPv4Fields = [...document.querySelectorAll('[data-current-ipv4-placeholder]')];
   const dashboardIPv4 = document.querySelector('[data-dashboard-ipv4]');