Constant CHANNEL_SIG_MAX_AGE_SECS 

const CHANNEL_SIG_MAX_AGE_SECS: i64 = JEKT_SIG_MAX_AGE_SECS; // 300i64

Anti-replay window for cross-channel channel_sig — SPEC_JEKT_CROSS_CHANNEL_TRUST_2026_09_02.md §D6: host-tier’s tighter JEKT_SIG_MAX_AGE_SECS, NOT LAN/WAN’s wider one. A cross-channel forward is a same-machine HTTP call to 127.0.0.1; it has no real-network latency budget to accommodate, for the same reason host-tier doesn’t.