Add managed TLS interoperability and persisted credentials

docs/porting-to-dotnet.md

@@ -1,6 +1,8 @@
 # Porting VoiceCat to pure .NET / C#
 
-**Status:** initial wire/crypto slice implemented under `dotnet/`; later phases remain planned.
+**Status:** wire/media crypto and TLS/exporter foundations implemented under `dotnet/`,
+including C++ interoperability, persisted TOFU, and compatible server credentials.
+Codec/audio, managed server/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.
 **Scope:** replace the C++ core (`libvoicecat`), the C++ server, the C++ `vccli`, and the
@@ -676,6 +678,16 @@ not assumed.
 **Exit criterion:** C# client completes a TLS 1.3 handshake with the C++ server, derives
 matching media keys, and pins the leaf fingerprint.
 
+**Checkpoint (2026-09-15):** implemented nonblocking managed TLS, handshake-time
+exporters, explicit certificate acceptance, persisted TOFU, and native-compatible
+credentials. The C++ TLS oracle authenticates a media challenge in both directions
+over an actual socket, proving exporter compatibility. Tests also cover managed
+fragmented loopback, first-connect acceptance, changed-pin rejection, TLS 1.2 rejection,
+close_notify/abrupt EOF, restart persistence, and import of C++ credential files.
+Socket orchestration remains a transport-owner responsibility; the complete managed
+server and client are later phases. See `dotnet/README.md` for the required native
+interoperability test command.
+
 ---
 
 ### Phase 3 — Codec + DSP (est. 1 week)