Keep old pages readable, detect stale settings writes, make backups honest

- Own CSS is parsed on write only. A page whose stored CSS no longer
  passes a stricter rule answers 200 and opens in the editor; that one
  block loses its CSS. A document read several times in one request is
  validated once.
- Settings and theme refuse a write from an outdated form.
- A backup fails when a media file does not arrive completely and
  leaves no half directory behind; rotation counts intact backups only.
- The archive update takes its backup behind the maintenance page.
- A package import puts all media in place before removing the old
  ones, reports honestly when that fails and keeps a maintenance state
  that was already on.
- Restoring replaces the SQLite file in one move and points at pending
  migrations.
- Six irreversible actions ask first, in a dialog of the admin's own.
- Ctrl+S in the editor takes the field being typed in along; Delete
  no longer removes a block while a dialog is open.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

src/Content/DocumentValidator.php

@@ -9,6 +9,9 @@ final class DocumentValidator
 {
     private bool $writing = false;
 
+    /** @var array<string, true> beim Lesen bereits geprüfte Dokumente dieser Anfrage */
+    private array $passed = [];
+
     public function __construct(private StyleCompiler $styles = new StyleCompiler(), private CustomCode $code = new CustomCode(), private ?PluginRegistry $plugins = null)
     {
     }
@@ -59,6 +62,24 @@ final class DocumentValidator
      *                             lässt unpassende Eigenschaften ohnehin nicht durch.
      */
     public function validate(array $document, bool $requireHeading = true, bool $writing = false): void
+    {
+        // Beim Lesen wird dasselbe Dokument in einer Anfrage oft mehrfach geholt (Seite,
+        // Brotkrumen, strukturierte Daten). Geprüft wird es einmal; der Schlüssel ist sein Inhalt,
+        // ein geändertes Dokument ist also ein anderes.
+        $seen = null;
+        if (!$writing) {
+            $seen = hash('xxh128', serialize($document)).($requireHeading ? '1' : '0');
+            if (isset($this->passed[$seen])) {
+                return;
+            }
+        }
+        $this->check($document, $requireHeading, $writing);
+        if (null !== $seen) {
+            $this->passed[$seen] = true;
+        }
+    }
+
+    private function check(array $document, bool $requireHeading, bool $writing): void
     {
         $this->writing = $writing;
         $schemaVersion = $document['schemaVersion'] ?? null;
@@ -133,7 +154,7 @@ final class DocumentValidator
                 $this->require(is_string($key) && strlen($key) <= 110 && is_string($hash) && 1 === preg_match('/^[a-f0-9]{8}$/D', $hash), 'Ungültiger Vermerk zur Übersetzung.');
             }
             try {
-                $this->validate(Translations::apply($document, $locale), $requireHeading, $this->writing);
+                $this->check(Translations::apply($document, $locale), $requireHeading, $this->writing);
             } catch (InvalidDocument $error) {
                 throw new InvalidDocument(sprintf('%s (%s): %s', Languages::CATALOG[$locale]['name'], $locale, $error->getMessage()), previous: $error);
             }
@@ -171,7 +192,17 @@ final class DocumentValidator
             // and is answered in the controller, not here.
             $this->require(CustomCode::supports($schemaVersion), 'Own code requires schema v13.');
             $this->require(is_string($block[$own]), sprintf('"%s" must be text.', $own));
-            'css' === $own ? $this->code->checkCss($block[$own]) : $this->code->checkScript($block[$own]);
+            // Eigenes CSS wird nur beim Schreiben geparst. Was gespeichert ist, galt beim Speichern;
+            // ist eine Regel inzwischen strenger, lässt compileCss() das CSS dieses einen Blocks
+            // weg (ADR 116). Hier beim Lesen zu werfen hieße: die Seite antwortet mit 500 und lässt
+            // sich nicht einmal mehr zum Reparieren öffnen.
+            if ('css' === $own) {
+                if ($this->writing) {
+                    $this->code->checkCss($block[$own]);
+                }
+            } else {
+                $this->code->checkScript($block[$own]);
+            }
         }
         if (isset($block['style'])) {
             // Free styling: any property of StyleSchema, per device, with an optional hover value.