- Add ReservationError::AlsaError variant; stop conflating ALSA
enumeration errors with DbusError.
- Mirror ReservationError variant set on the non-Linux stub so cross-
platform pattern matching compiles on every target.
- Add empty Drop to stub for RAII symmetry with the Linux variant.
- Collapse ReservationState to its real Task 1 shape (Degraded only);
Task 2 reintroduces Active when it has real fields.
- Rewrite acquire() doc-comment to honestly describe Task 1's behaviour
and hint at Task 2's full failure-mode set.
No behaviour change. Foundation commit for Task 2.
cc
vicrodh
f0ea0c88ec