refactor: DiviWriteAbility base and shared DiviErrors (H4)

The five Divi write tools extend DiviWriteAbility (final permission and
execute, change() per tool, shared output schema). DiviErrors holds the
unknown-node, position and compose-error mapping; DiviContentComposer uses
the same mapping (ledger T9). ToolNamingTest skips abstract classes.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Integrations/Divi/Pages/DiviWriteAbility.php

@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Integrations\Divi\Pages;
+
+use LIT\MCP\Abilities\Ability;
+use LIT\MCP\Abilities\ToolResult;
+use WP_Error;
+
+/**
+ * The frame of the Divi write tools (spec §5.6): permission and execute both load the page
+ * through DiviWriter::page() (rights, Divi layout, tree_rev lock – execute never trusts state
+ * from permission), the tool changes the tree in change() – only when its whole input
+ * validated, all or nothing (ruling S39) – and DiviWriter::save() stores it and builds the
+ * result. The composition is bound to the page (DiviWriter::composition(), ruling S22).
+ */
+abstract class DiviWriteAbility implements Ability
+{
+    public function __construct(protected DiviWriter $writer)
+    {
+    }
+
+    /**
+     * Changes the tree of $page, or returns why nothing is written. Client values enter the
+     * tree only through $composition (Composer / TreeEditor).
+     *
+     * @param array<string, mixed> $input
+     */
+    abstract protected function change(DiviPage $page, array $input, DiviComposition $composition): DiviChange|WP_Error;
+
+    public function outputSchema(): ?array
+    {
+        return ToolResult::schema(['tree_rev' => ['type' => 'string']], ['tree_rev']);
+    }
+
+    public function isDirect(): bool
+    {
+        return true;
+    }
+
+    final public function permission(array $input): bool|WP_Error
+    {
+        $page = $this->writer->page($input);
+
+        return $page instanceof WP_Error ? $page : true;
+    }
+
+    final public function execute(array $input): mixed
+    {
+        $page = $this->writer->page($input);
+        if ($page instanceof WP_Error) {
+            return $page;
+        }
+
+        $change = $this->change($page, $input, $this->writer->composition($page));
+        if ($change instanceof WP_Error) {
+            return $change;
+        }
+
+        return $this->writer->save($this->name(), $page, $change, $input);
+    }
+}