Half-width of the per-item power jitter band, in raw combat-power units.
Each rolled item gets a uniform integer draw from [-POWER_JITTER_HALF, +POWER_JITTER_HALF] using the session-seeded RNG already in scope, so:
pending_items are the items already rolled in the same batch open; they
are not in character_state.inventory yet, but the empty-slot guarantee
must treat their slots as filled.