Ctrl+b (tmux prefix) not passed through to parent tmux session

When running Claude Code inside tmux, Ctrl+b is captured by Claude Code and never reaches tmux. This makes it impossible to detach, switch sessions, or use any tmux keybindings without exiting Claude first.

Especially painful on mobile terminals (e.g., Echo on iPhone) where there's no easy way to open a second connection to manage tmux.

Expected behavior: Ctrl+b (or whatever the tmux prefix is) should be passed through to the parent tmux session.

Workaround: Exit Claude Code first, or manage tmux from a separate terminal session.