Detection

Before it can drive a pane, cyber-mux has to know which multiplexer it is inside. Detection is two-mode.

1. Fast-path / override

If CYBER_MUX is set to a known value (tmux, herdr, wezterm, zellij, screen, or none), it is trusted outright. CYBER_MUX_PANE carries the pane id alongside it.

This also acts as an override: CYBER_MUX=none forces no-mux behavior even inside a real multiplexer.

screen is detected, but not drivable

screen is a recognized value — pinning it, or running under a real screen session, is reported truthfully rather than silently ignored — but cyber-mux cannot drive GNU Screen, so it rejects the value with a named error instead of returning a backend. Screen addresses its split regions positionally (no per-pane id) and leaves $WINDOW unset in panes opened via screen -X, so a pane has no stable identity to send to, read from, or self-identify by — the affordance every driven backend depends on. Use tmux, herdr, or wezterm.

export CYBER_MUX=tmux CYBER_MUX_PANE=%3

cyber-mux doctor prints exactly this line for your current pane, so you can pin it and skip discovery.

2. Ancestry discovery

With no fast-path set, cyber-mux walks the process ancestry from its own PID (ps -o ppid=,comm=), looking for a tmux, herdr, wezterm/wezterm-gui/wezterm-mux-server, zellij, or screen ancestor. It walks past the tool’s own shell — the immediate parent is often not the human’s pane.

If the walk is inconclusive (e.g. ps is unavailable), it falls back to the $TMUX / $HERDR_ENV / $WEZTERM_PANE / $ZELLIJ environment hints — the fast-positive signal used only when the walk itself found nothing. WezTerm has no separate “inside wezterm” flag the way $TMUX/$HERDR_ENV are: $WEZTERM_PANE is the hint, doubling as both the signal and the pane id. Zellij sets $ZELLIJ inside any Zellij pane, the same ambient-flag shape as $TMUX/$HERDR_ENV. These hints are never trusted over ancestry — an ancestry-verified multiplexer always wins over a stale env hint. The Zellij adapter requires Zellij ≥ 0.44.1, the release that added per-pane CLI addressing.

Self pane

cyber-mux resolves its own pane from environment alone (no ps walk): the CYBER_MUX_PANE fast-path, then $TMUX_PANE (tmux), then $HERDR_PANE_ID (herdr), then $WEZTERM_PANE (wezterm), then $ZELLIJ_PANE_ID (zellij). This is the identity key a session uses to address itself.