TrimEnd('0','f') missed Library/unity default resources built-ins whose GUID
has no all-zero or all-f suffix (e.g. 0000000000000000e000000000000000, the
LegacyRuntime font / Cube mesh in 6000.3.24f1). Ask AssetDatabase instead: a
real project asset is always a main or sub-asset under Assets/ or Packages/;
built-ins are neither. Also add a Clear button beside the stale-value warning
so a non-resolving stored key can be cleared without picking a substitute
asset first (drawing still never rewrites a stored value on its own).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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