Literal ^[[I escape sequence printed to terminal when reattaching to a background session
Open 💬 0 comments Opened Jul 5, 2026 by av-bw
Description
When switching back to a terminal tab running a Claude Code background session (bg) after being away, the raw escape sequence ^[[I is printed as literal text instead of being interpreted by the terminal, right before the session's "currently running as a background agent" message.
Steps to reproduce
- Start a Claude Code session, background it (bg / detach)
- Switch away to another terminal tab for a while
- Switch back to the tab with the backgrounded session
- Observe garbled output at the top, e.g.:
^[[ISession <uuid> is currently running as a background agent (bg). Use `claude agents` to find and attach to it, or add --fork-session to branch off a copy.
[worker crashed (exit 1 — exit_with_message) — respawning…]Expected
No raw escape codes printed to terminal; the reattach message should render cleanly.
Environment
- macOS (Darwin), iTerm2 (or default Terminal)
- Multiple Claude Code bg sessions open across tabs
Notes
Suspect this is a focus-reporting escape sequence (\x1b[I, DECSET 1004) leaking through on reattach, possibly a PTY raw-mode / buffering issue when the worker process respawns. Workaround: running reset in the terminal clears it.