[tobsch]

Fixes #356 — root cause found and fix verified live (patched into the running container's dist).

Root cause

deriveHardwareAddress(sourceMac, zoneId) in airplayInstance.ts builds each zone's RAOP identifier by
adding zoneId to the last byte of the zone's sourceMac:

bytes[5] = ((bytes[5] ?? 0) + (zoneId & 0xff)) & 0xff;

But the per-zone sourceMac values are not unique — several zones share one (in this install:
…1067, …1068, …1069, …106A each appear on two zones). Adding zoneId on top then collides whenever
sourceMacLastByte + zoneId coincides:

zone	sourceMac	+zoneId	identifier
5 Wohnzimmer	…1068	+5	…106D
6 Elternbad	…1067	+6	…106D ⚠️
9 Küche	…106A	+9	…1073
10 Außenbereich	…1069	+10	…1073 ⚠️

So Wohnzimmer/Elternbad and Küche/Außenbereich each advertised the same _raop._tcp identifier (only the
port differed). An AirPlay client that selects by identifier lands on whichever resolves first — verified:
streaming to 88AEDD68106D played into Elternbad, not the intended Wohnzimmer.

Fix

zoneId is unique per zone, so derive the last byte from it directly rather than adding it to a non-unique
base:

bytes[5] = zoneId & 0xff;

Verification (dist-patched into the running container)

All 11 zones now advertise distinct identifiers, and every zone shows up in discovery (previously the
colliding ones shadowed each other):

…1001 Kinderzimmer Linda   …1005 Wohnzimmer     …1009 Küche
…1002 Kinderzimmer Louise  …1006 Elternbad      …100A Außenbereich
…1004 Esszimmer            …1007 Elternschlafz. …100B Gästebad
                           …1008 Backupküche    …100C Einliegerwohnung

Streaming an AirPlay tone to Wohnzimmer's id (…1005) now lands in the right room —
[Input|AirPlay][Wohnzimmer] airplay pcm chunk … zoneId=5.

(Deeper cleanup out of scope here: the per-zone sourceMac values probably shouldn't be assigned with
duplicates in the first place. Making the identifier derive from the unique zoneId fixes the user-visible
collision regardless.)

[rudyberends]

Went with a slightly different fix: the address is now derived from a SHA-256 hash of serial+zoneId, with the locally-administered bit set. Setting the last byte to zoneId alone fixes a single server, but two audioservers with near-adjacent serials (identical first five bytes) would still collide on equal player ids — hashing the full pair covers that case too, and the locally-administered bit keeps the synthetic address out of the real MAC space. Unit tests cover both collision classes, including your ..68+5 == ..67+6 case.