fix(android): pass PROTOCOL_DNS_SD so mDNS registration works

Android 16 added NsdManager.checkProtocol(): registerService with protocol
0 threw IllegalArgumentException: Unsupported protocol — silently, since
the old code swallowed the exception into a dead reflection fallback and
start() overwrote the failure status with the Listening line. mDNS never
actually advertised (the Phase 8 session streamed via --peer, masking it).

Also advertise after the listening status so a registration failure stays
visible, and log the exception and the registration success.

Validated live on the Fairphone 6: the desktop --discover lists the phone
and a full --send session decodes (in-band SPS 320x240 -> 2496x1040) and
renders.

.agents/MEMORY.md

@@ -304,6 +304,32 @@ Validation: `gradle :app:assembleDebug :app:testDebugUnitTest` green
 (25/25, full --rerun-tasks rebuild, only two pre-existing warnings);
 `meson test` 5/5 unchanged (no C++ touched).
 
+### Discovery bug found and fixed on-device (2026-09-10, same day)
+
+The user reported the desktop sender never discovered the phone.
+Root cause (found live on the Fairphone 6): `registerService(info, 0,
+listener)` — Android 16's `NsdManager.checkProtocol()` rejects protocol
+`0` with `IllegalArgumentException: Unsupported protocol`. The old code
+swallowed it into the dead reflection fallback, and `start()` posted the
+"Listening…" status AFTER advertiseNsd, overwriting the failure text — so
+mDNS never advertised and Phase 8's NSD validation was only ever "no
+crash" (8.5 streamed via --peer, masking it).
+
+Fixes in `ReceiverPipeline.advertiseNsd()`/`start()`:
+- pass `NsdManager.PROTOCOL_DNS_SD`;
+- advertise AFTER the listening status so a failure stays visible;
+- `Log.e` the registration exception; `Log.i` on registered success.
+
+On-device validation (adb, live): `mDNS registered:
+screencast._screencast._tcp` in logcat; `dumpsys servicediscovery` shows
+the active Advertiser (key diagnostic: `mClientRequests` empty == no
+request ever issued); desktop `avahi-browse` and `screencast --discover`
+list the phone at 192.168.178.29:5005; a 25s `--send --target monitor
+--peer 192.168.178.29:5005` session decoded (in-band SPS reconfigured
+320x240 → 2496x1040) and rendered (screencap mean brightness 0.51).
+Note: with both the Pi and the phone on the LAN, plain `--send` refuses
+(two receivers found) — target the phone with `--peer`.
+
 Still open (accepted, needs a device or a new test dep):
 
 - Untested on device: `setOutputSurface` mid-session (surface switch) and