CngxChipGroupHost

Parent contract every chip-group molecule (CngxChipGroup single, CngxMultiChipGroup multi) provides via useExisting. CngxChipInGroup leaves inject this token (NOT optional) - never the concrete group class - so the leaf stays decompose-ready and free of cyclic type dependencies, and the Phase 5 split between single + multi groups can share the same leaf implementation.

Selection state is queried via isSelected(value) and mutated via toggle(value) / remove(value). isDisabled is a Signal<boolean> so the leaf's reactive aria-disabled and the disabled-cascade derivation track it without re-injection. Per reference_atomic_decompose §4 - leaf communicates with its parent via DI token, never via concrete parent-class injection.

Mode (single vs multi) is intentionally NOT exposed on this contract: the leaf does not branch behaviour on mode, and no consumer / bridge surface in scope reads it. A future feature that needs mode discovery can extend the interface then; until then the field stays out of the public surface.