August 22, 2026 · Joy
Missed the output? Replay it from exact evidence
You look away. The agent prints a stack, a test failure, a file path — then more output lands on top. The terminal tab is still “there.” The line you needed is not.
People guess. They ask the agent “what just happened?” The agent guesses too, from a prompt that no longer contains the bytes.
That is not evidence. That is folklore.
Replay is not scrollback
Scrollback is a UI buffer. It truncates. It dies with the tab. It is not indexed to the session.
Replay means playing output back from durable execution evidence: the same session, the same events, the same cursor. You can miss a pane and still see what ran.
JoyMux is built for that beat: Missed output? Replay it.
Why this matters for coding agents
Agent runs are long and uneven. You will not watch every line. If the only copy of truth is a live PTY, you are one crash or one overflow away from “I think it said…”
Exact replay is how you debug without re-running. Re-running is how you pay twice.
Pair it with hard-reset to the same state when the process itself died — resume the session, replay what you missed, continue.