Terminal escape sequences printed on startup in tmux #16547

Bug Description

When opening opencode inside a tmux session, terminal escape sequence responses are printed as text instead of being consumed properly.

Environment

• Terminal: Alacritty (with TERM=xterm-256color)
• Shell: zsh
• Terminal multiplexer: tmux (TERM=tmux-256color)
• Config files:
  • ~/.config/alacritty/alacritty.toml:

    general.import = [ "~/.config/omarchy/current/theme/alacritty.toml" ]
    
    [env]
    TERM = "xterm-256color"

  • ~/.config/tmux/tmux.conf:

    set -g default-terminal "tmux-256color"
    set -ag terminal-overrides ",*:RGB"
    set -g allow-passthrough on
    set -g escape-time 0
    set -g focus-events on

  • ~/.zshrc:

    alias oc='opencode'
    eval "$(starship init zsh)"

Steps to Reproduce

1. Open alacritty terminal
2. Start tmux: tmux
3. Run opencode: opencode (or oc)
4. Observe the escape sequences printed at the prompt

Expected Behavior

opencode should start normally without printing terminal escape sequences.

Actual Behavior

The following escape sequences are printed:

omarchy master ❯ ?1016;0$y
/2026;2$y_

Additional Context

• Does NOT occur when running opencode outside of tmux (directly in alacritty)
• Does NOT occur in tmux when running other interactive terminal applications
• The sequences appear to be DECRPM (DEC Private Mode Report) responses:
  • ?1016;0$y - Cursor Attribute Report response
  • /2026;2$y - Cursor Shape query response

These sequences suggest opencode is querying terminal cursor capabilities on startup, but the responses are leaking through and being printed as text instead of being consumed properly.

Attempted Fixes

• Added set -g allow-passthrough on to tmux config (already present)
• Added set -ag terminal-features 'alacritty:clipboard' to tmux config
• Neither resolved the issue