Add managed TLS interoperability and persisted credentials

docs/security.md

@@ -49,6 +49,16 @@ This is a known limitation of the current design. Closing it properly requires b
 Ed25519 key into the TLS cert (e.g. as a SubjectAltName or extension), which is a planned
 future improvement. Until then, clients display both values but gate on the cert fingerprint.
 
+**Managed rewrite checkpoint:** `dotnet/` uses nonblocking BouncyCastle TLS 1.3 and
+captures directional exporters during handshake completion. Its client requires an
+explicit leaf-fingerprint acceptance callback; PKI validation remains unimplemented.
+New managed server certificates include the Ed25519 public key in SAN URI
+`urn:voicecat:identity:ed25519:<lowercase-public-key-hex>`. Existing C++ credentials
+are imported unchanged. Verifying that URI against the declared ServerHello identity
+is still deferred to the managed session layer; leaf-certificate TOFU remains the
+trust gate. Missing members of a persisted credential set cause startup rejection
+rather than automatic identity rotation. See [api-dotnet.md](api-dotnet.md).
+
 Client certificates are reserved for a future "key-based identity" option (see roadmap) but
 are not required in v1.