Environment: pooled iPhone 18 Pro iOS simulator, 402x874 logical points (1206x2622 raw recording), T3 Code development client, light appearance, Replay (dev), Multi turn scenario. Each commit runs its own Metro bundle and fresh dev server state.

Set T3CODE_DEV_SEED=0 before starting each dev server. Seed a synthetic Sample project using seed-public.mjs. Run set-project.mjs <checkout> <server-port> after seeding to select Replay. The uploaded seed is the executed seed with the synthetic project directory changed from a private literal to an argument.

Run lost-reply-proxy.mjs with REPO=<checkout>, TARGET=<backend-port>, PORT=<device-reachable-proxy-port>. Pair the app through that proxy. Rename the connection Evidence before capturing to avoid private environment labels.

Open Sample project's new-thread composer and run reproduce.mjs. The proxy forwards orchestration.launchThread, suppresses all subsequent messages on that socket, waits for the matching launch Exit from the server, drops the accepted reply, terminates the sockets and blocks reconnects. The driver restores connectivity after five seconds without restarting the app or editing the queued message. No second Send tap is made.

AI-assisted; verified with the tests and tools listed above.