nx_tls13_client_session_derive_app.nx

nx_tls13_client_session_derive_app.nx -- step 3c.5 of the nx_https_client wiring arc. Runs the SECOND HALF of the RFC 8446 §7.1 key schedule cascade to derive the application-traffic keys, advancing the session from WAIT_APP_KEYS to CONNECTED. After this primitive returns OK, the session is fully usable for application-data send/recv. Cascade (continuing from where 3c.2 left off): handshake_secret (from 3c.2) | v Derive-Secret(., "derived", H_empty) = derived_2 | v IKM = 0^HashLen HKDF-Extract(salt=derived_2, IKM=0) = master_secret | v salt = master_secret; context = H2 = hash(CH..CF) +--> Derive-Secret(., "c ap traffic", H2) = c_app_traffic_secret_0 +--> Derive-Secret(., "s ap traffic", H2) = s_app_traffic_secret_0 then per-secret expand: key = HKDF-Expand-Label(secret, "key", "", 32) iv = HKDF-Expand-Label(secret, "iv", "", 12) The transcript at this point covers CH..client_Finished (CF was appended in 3c.4's emit). H2 = transcript snapshot. Once derived, app_seq counters are reset to 0 (per-direction AEAD nonce sequence starts fresh for application data). State advances to CONNECTED -- application send/recv is now safe. Public API: nx_tls13_client_session_derive_app(session) -> verdict nx_tls13_derive_app_verdict_is_valid(v) -> 0|1 Sealed verdict: NX_TLS13_DERIVE_APP_OK keys derived, state CONNECTED NX_TLS13_DERIVE_APP_BAD_STATE session not at WAIT_APP_KEYS