Copying subimage output to Partition

[eadwu]

How would I vendor say a sysext image into a partition?

My naive attempt

[Partition]
Type=linux-generic
Label=%M_sysext
Format=erofs
CopyBlocks=%O/sysext_%v.raw:/
Minimize=yes
Compression=zstd

results in Failed to expand specifiers in CopyBlocks= source path, ignoring: %O/sysext_%v.raw:/

Same with CopyFiles, though the docs imply this one is from image.

Or should the image be copied into the main image?

[MoltenArmor]

This is a systemd-repart partition definition, not a mkosi config. systemd-repart will not understand mkosi's specifier. Consider adding this to your subimage's mkosi.postoutput: cp $OUTPUTDIR/xxx.raw $OUTPUTDIR/<YOUR BASE SUBIMAGE>/.