Add encrypted managed UDP relay and native voice conformance

docs/porting-to-dotnet.md

@@ -3,7 +3,7 @@
 **Status:** wire/media crypto and TLS/exporter foundations implemented under `dotnet/`,
 including C++ interoperability, persisted TOFU, compatible server credentials,
 codec/DSP wrappers, desktop native staging, and the initial managed TLS control server.
-Phase 4 remains in progress; UDP relay, complete session administration, device audio,
+Phase 4 remains in progress; complete session administration, device audio,
 managed client state, and UI phases remain planned.
 See `dotnet/README.md`, `docs/api-dotnet.md`, and `PROGRESS.md` for verification and next steps.
 **Target runtime:** .NET 10 LTS (in-service to Nov 2028), with .NET 11 as the follow-on.
@@ -729,9 +729,24 @@ the existing BouncyCastle dependency with a strict libsodium PHC parser, not a n
 Konscious dependency. Native database tests prove password compatibility in both
 directions without resets. SQLite uses `Microsoft.Data.Sqlite.Core` 10.0.5,
 SQLitePCLRaw bundle 3.0.2 and explicitly pinned SourceGear SQLite 3.50.4.2.
-See `docs/api-dotnet.md` for limits. UDP voice, streams, protected joins, moderation,
-admin handlers and production configuration remain pending. The exit criterion
-below has not yet been met.
+See `docs/api-dotnet.md` for limits. This first checkpoint did not include UDP voice,
+streams, protected joins, moderation, admin handlers or production configuration.
+The subsequent voice checkpoint is described below.
+
+**Voice checkpoint:** the managed server now advertises UDP, issues session-bound
+tokens, implements voice subscription and multi-stream signaling, and relays encrypted
+Opus with recipient-specific counters. The first UDP endpoint is fixed for the session;
+reconnect for endpoint changes. Immutable routing snapshots separate control handlers
+from the UDP crypto owner. Real-socket tests cover replay/forgery/SSRC rejection,
+channel/subscription isolation, stream stop and disconnect. A native client oracle
+exercises bidirectional microphone and screen audio in mono and stereo. The fan-out
+core has a 50-subscriber allocation regression test; transport scheduling and the
+BouncyCastle crypto fallback are excluded from its zero-allocation guarantee.
+Two real C++ `vccli` processes also pass join/text/bidirectional voice tests using
+finite `--test-tone-ms` external capture/playback. The transport load test delivers
+all 2,500 recipient packets from a sender paced at 50 pps to 50 subscribers.
+Administration, protected joins, production configuration and media-aware reaping
+still remain before Phase 4 completion.
 
 1. `VoiceCat.Server`: accept loop, `ConnSession` protocol handling, session registry.
 2. `Db` on `Microsoft.Data.Sqlite` — same schema. **Resolve the Argon2id hash-compat