Root cause: when the LLM runs `cmd &`, bash forks the process and
exits immediately. The forked process inherits Node's piped stdout/
stderr FDs. Node.js waits for all holders of those FDs to close before
firing the 'close' event — so the tool hangs until the background
process exits (which for a server is never).
Fix: add rewriteBackgroundCommand() in bash.ts. Before exec, detect
commands with a trailing & background operator and inject
>/dev/null 2>&1 before the & when stdout is not already redirected.
This severs the pipe inheritance so Node gets 'close' immediately
when the shell exits.
Guards:
- Commands already redirecting stdout (>, >>, &>, |) are not rewritten
- && (logical AND) is not affected
- & inside single-quoted strings is not affected
- A brief onUpdate advisory is surfaced when rewrite happens so the
LLM knows to prefer nohup/setsid for robust detachment
Export rewriteBackgroundCommand from pi-coding-agent for testability.
Tests: bash-background.test.ts — 12 cases covering no-op paths,
rewrite paths, compound commands, and already-safe nohup patterns.
Closes#733
a3ff25c668