Persist diskName per attachment in the JSON metadata (feature request) #37

Is your feature request related to a problem?

I have several disks configured (e.g. s3 and local) and I'd like to spread uploaded photos across both of them — choosing the target disk dynamically at upload time rather than hardcoding a single disk per attribute via the @attachment({ disk: '...' }) decorator.
The problem is that the disk (or diskName) is not persisted in the JSON metadata stored in the database. As a result, once a file is written, the package has no record of which disk it actually lives on — it always resolves the disk from the decorator/config at read time. This makes it impossible to reliably serve, generate URLs for, or delete files when different rows of the same model are stored on different disks.

Describe the solution you'd like

Store the diskName per attachment inside the persisted JSON metadata, alongside the existing fields (name, extname, mimeType, size, etc.). On read (URL generation, deletion, etc.), the package should use the diskName from the stored metadata when present, and only fall back to the decorator/config disk when it's absent (for backward compatibility).

Describe alternatives you've considered

Hardcoding the disk per attribute via the decorator, but this prevents distributing files of the same model/attribute across multiple disks.

Additional context

This would enable use cases such as load-balancing storage across multiple backends, gradual migration between disks, or routing files to different disks based on runtime conditions.