Symptom

Desktop app could not discover a Krill server running on the same machine. Remote servers (on separate Pi nodes) appeared normally. The demo-recording pipeline was completely blocked because it co-locates the app and a sandbox server on the same box.

Root cause

ClientBeaconWireHandler.handleIncomingWire filtered “own” beacons by comparing wire.host() == hostName. When app and server share a host, both advertise the same hostname in their beacons, so the server’s beacon was indistinguishable from the client’s own and was silently dropped — even though their installId values are different.

Fix

• composeApp/src/commonMain/kotlin/krill/zone/app/io/beacon/BeaconWireHandler.kt: replaced the hostname equality check with wire.installId == selfId(). Added selfId: () -> String = installId constructor parameter (default preserves existing behavior) so the seam is testable without reading the filesystem.
• Added composeApp/src/desktopTest/kotlin/krill/zone/app/io/beacon/ClientBeaconWireHandlerSelfFilterTest.kt with three cases: own-beacon dropped, same-host server beacon accepted, remote server beacon accepted.

Prevention

• Use installId (stable UUID) for any “is this my own beacon?” check, not hostName. Hostname equality is not a unique identity — it breaks whenever two processes share a host.
• The connect guard two lines below the dropped check already used installId correctly; the self-filter should have matched it.
• When a production function calls a platform expect-val (installId, hostName, platform), inject it as a constructor parameter with a default so the unit is testable without an environment.