build.asset-missing

Meaning

a file the scene names (an asset, a texture its material file names, or an asset of a prefab a script spawns, resolved from the scene's folder) is not in this revision where it resolves; Play and export refuse the scene (content-incomplete), a bare argus run draws a placeholder. Also on a scene write (scene.patch and the other structural tools), checked on disk

Fix

put the file where the message says, or fix the path: a scene's asset paths resolve from the scene file's folder, a material's textures from the material file's folder, never the project root