fix: global library edits check private and scheduled pages, name the backup on failure (P8a, P14)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Abilities/WriteFailed.php

@@ -32,7 +32,7 @@ final class WriteFailed extends RuntimeException
         public readonly ?int $postId,
         public readonly ?int $revisionId,
         ?Throwable $previous,
-        string $detail,
+        private string $detail,
         public readonly ?string $state,
         public readonly ?string $hint,
         public readonly array $details
@@ -82,6 +82,28 @@ final class WriteFailed extends RuntimeException
         return new self($reason, false, $postId, $revisionId, $cause, $detail, $state, $hint, $details);
     }
 
+    /**
+     * The same failure with $details merged into its client details; a non-null $hint or $state
+     * replaces the current one (see rolledBack()/partial()). For callers that learn about
+     * something kept (e.g. a backup) only after the failure was thrown.
+     *
+     * @param array<string, mixed> $details
+     */
+    public function withDetails(array $details, ?string $hint = null, ?string $state = null): self
+    {
+        return new self(
+            $this->reason,
+            $this->rolledBack,
+            $this->postId,
+            $this->revisionId,
+            $this->getPrevious(),
+            $this->detail,
+            $state ?? $this->state,
+            $hint ?? $this->hint,
+            array_merge($this->details, $details)
+        );
+    }
+
     public function toError(): WP_Error
     {
         return $this->rolledBack