D422 - A title's writable device paths are modeled as a per-title sandbox, not a special case

Status: decided Date: 2026-08-31

A guest's writable device paths (its per-title save area and mounted removable-storage stand-ins) are layers in the existing overlay filesystem, not a new subsystem; guest writes to them persist across runs by default.

Why: The overlay filesystem already builds a read-only base tree with a writable per-title layer over it, so the console's sandboxed device paths are additional writable mount entries in that same mechanism. Persisting a title's writes by default keeps the saves and reports a run produces available to the next one; a caller that wants a clean slate selects ephemeral retention instead.

Rejected: special-casing the one call site that first hit this - the same shape recurs at every writable path a guest opens.