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, rmux, herdr, wezterm, zellij, cmux, otty, 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, rmux, herdr, wezterm, zellij, cmux, or otty.

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, rmux-daemon (or bare rmux), 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. cmux and otty are GUI apps whose process names are not discoverable via ancestry, so they are detected by env hint only.

If the walk is inconclusive (e.g. ps is unavailable), it falls back to the $RMUX / $TMUX / $HERDR_ENV / $WEZTERM_PANE / $ZELLIJ / $CMUX_WORKSPACE_ID / $OTTY_PANE_ID environment hints — the fast-positive signal used only when the walk itself found nothing, checked in that order (rmux before tmux, since an rmux pane sets $TMUX too — see below). WezTerm has no separate “inside wezterm” flag the way $TMUX/$HERDR_ENV/$RMUX 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. cmux sets $CMUX_WORKSPACE_ID and otty sets $OTTY_PANE_ID. These hints are never trusted over ancestry — an ancestry-verified multiplexer always wins over a stale env hint. The Zellij adapter requires Zellij ≥ 0.45.0 — 0.44 added per-pane CLI addressing, 0.45.0 added the --no-focus flag every focus-preserving open passes.

Self pane

cyber-mux resolves its own pane from environment alone (no ps walk): the CYBER_MUX_PANE fast-path, then $RMUX_PANE (rmux), then $TMUX_PANE (tmux), then $HERDR_PANE_ID (herdr), then $WEZTERM_PANE (wezterm), then $ZELLIJ_PANE_ID (zellij), then $CMUX_SURFACE_ID (cmux), then $OTTY_PANE_ID (otty). rmux is checked before tmux because an rmux pane sets $TMUX_PANE too, for tmux compatibility. This is the identity key a session uses to address itself.