These docs are under active development and cover the v0.20 Kobicha security model.
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§3.3

Allocation

LUIDs MUST be allocated by the kernel.

§3.3.1 Uniqueness scope

Each LUID MUST be unique within a single boot session.

LUID values MUST NOT be assumed unique across reboots. A value allocated in one boot session MAY be reused in a subsequent boot session.

§3.3.2 Monotonicity

The kernel MUST allocate LUIDs in strictly monotonically increasing order within a boot session, treating the two fields as a single unsigned 64-bit integer (HighPart << 32 | LowPart).

The starting value of the allocation sequence after each boot is implementation-defined.

ⓘ Informative
Subsystems that define well-known LUID values (such as privilege identifiers) typically reserve values below the allocation starting point. The starting value should be chosen to leave room for current and future well-known values.

§3.3.3 Fabrication prohibition

Userspace code MUST NOT fabricate LUID values. All LUIDs MUST be obtained through the kernel allocation interface or from well-known constants defined in a Peios specification.