nx_tls13_server_session_test.nx

nx_tls13_server_session_test.nx -- verify server session skeleton allocates correctly + state machine enum is well-formed. Closed-form invariants: (a) Null inputs return null session (b) Valid inputs return non-null session at INIT state (c) server_random + x25519_priv are copied into owned buffers (not aliased to caller's input) (d) x25519_pub is derived from priv (matches the known-answer relation: pub = X25519(priv, basepoint)) (e) All state constants 0..N-1 are valid; out-of-range invalid (f) Session-new yields all secret-buffer pointers initialised to either non-null (active fields) or null (queued fields) per the documented contract expect_exit: 0 license_tier: ORIGINAL