chore: checkpoint web Blender migration source, tools and docs

Accumulated uncommitted work: GHOST Web backend, WebGL/GPU web layer,
web workflow engine and protocol, tooling, docs and task records.
Large generated evidence, user-testing archives, build snapshots and
imported test assets remain untracked.

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

blender-5.2.0/source/blender/blenkernel/BKE_cachefile.hh

@@ -4,6 +4,8 @@
 
 #pragma once
 
+#include <string>
+
 /** \file
  * \ingroup bke
  */
@@ -39,6 +41,11 @@ void BKE_cachefile_reader_open(CacheFile *cache_file,
                                const char *object_path);
 void BKE_cachefile_reader_free(CacheFile *cache_file, CacheReader **reader);
 
+/** Last native open diagnostic for this evaluated archive, owner and object path. */
+std::string BKE_cachefile_reader_error(const CacheFile *cache_file,
+                                     const Object *object,
+                                     const char *object_path);
+
 /**
  * Add a layer to the cache_file. Return NULL if the `filepath` is already that of an existing
  * layer or if the number of layers exceeds the maximum allowed layer count.