The recently merged manager-level locking for snapm uses /run/lock/snapm. The parent directory, /run/lock is now deprecated by systemd, and will be removed in systemd-v259:

https://lwn.net/Articles/1041316/

https://github.com/systemd/systemd/pull/38644

Downstream distributions and components that still wish to make used of the directory (serial port locks, lvm, legacy sysv subsystem locking) are encouraged to ship downstream tmpfiles configurations to preserve access to the path.

This is potentially problematic due to the fragmentation problems described by the Debian developers and keszybz: let's side-step the problem by having our own top level directory in /run:

 
 * /run/snapm/lock/ currently contains one file: manager.lock. Directory reserved for future expansion to snapshot-set level locking if required. * /run/snapm/mounts contains snapshot set mounts managed by snapm. One directory per mounted snapshot set /run/snapm/mounts/myset/...
 * (possibly) /run/snapm/scratch a size-constrained tmpfs instance used for temporary storage and working files

Moving the locking over is a simple task (modifying a few constants and testing). The additional directories (mounts etc.) will be added by their respective subsystems (e.g. in RHEL-111300)