Detection

resolveMux picks a backend for you, and throws if the process is in no supported multiplexer. When you want the detection result itself — the backend name, the pane, and how it was found, without the throw — call the probe directly. See Detection for the two-mode algorithm this implements.

probeMultiplexer is unchanged by resolveMux/MuxSession: it stays the raw, exec-first call below (it is what a session’s own detection runs internally, before there is a session to bind exec to). It is the non-throwing gate for a caller that runs with-or-without a multiplexer:

import { probeMultiplexer, resolveMux, nodeExec } from 'cyber-mux'

if (probeMultiplexer(nodeExec, process.env).mux !== 'none') {
  const mux = resolveMux(process.env)
  // ...
}

import { probeMultiplexer, currentPane, nodeExec, type MuxProbe } from 'cyber-mux'

probeMultiplexer(exec, env, opts?) → MuxProbe

Two-mode detection:

1. Fast-path — $CYBER_MUX (tmux | rmux | herdr | wezterm | zellij | cmux | otty | screen | none) is trusted outright, and also serves as an override (=none forces no-mux even inside a real multiplexer). $CYBER_MUX_PANE carries the pane id. screen is recognized here but is not a drivable backend — probeMultiplexer reports mux: 'screen', and resolveMux/resolveMuxAdapter then reject it with a named error rather than returning an adapter. Recognition is not support.
2. Discovery — otherwise, walk the process ancestry from $$, falling back to an env hint only when the walk is inconclusive: $RMUX → $TMUX → $HERDR_ENV → $WEZTERM_PANE → $ZELLIJ → $CMUX_WORKSPACE_ID → $OTTY_PANE_ID. $RMUX is asked before $TMUX — an rmux pane sets both, so $TMUX proves only “some tmux-language multiplexer”, and asking tmux first would drive an rmux session with the wrong binary. cmux and otty have no ancestry entry at all and are found by env hint alone.

const probe = probeMultiplexer(nodeExec, process.env)
// { mux: 'tmux', pane: '%3', via: 'ancestry' }

MuxProbe carries mux, an optional pane, and via ('env' when the fast-path answered, 'ancestry' when the walk did).

ProbeOptions

• discover — set false to skip the ancestry walk and answer none when the fast-path misses, for a caller that only trusts the explicit override.
• envPrefix — the environment-variable namespace the fast-path reads, without the trailing _PANE. Defaults to CYBER_MUX. See below.

currentPane(env)

This session’s own pane, resolved from env alone (no ps walk): the $CYBER_MUX_PANE fast-path, then $RMUX_PANE, $TMUX_PANE, $HERDR_PANE_ID, $WEZTERM_PANE, $ZELLIJ_PANE_ID, $CMUX_SURFACE_ID, $OTTY_PANE_ID (checked in that order — an rmux pane sets $TMUX_PANE too, so $RMUX_PANE must be asked first). Returns { mux, pane } tagged with the multiplexer, or undefined when the session is in no pane-carrying multiplexer. This is the mux-agnostic self-identity key that mux.callerPane() (and the raw callerPane) is built on.

Embedding under your own namespace

If you embed cyber-mux inside a host tool with its own environment convention, pass envPrefix so the fast-path reads your variables instead of CYBER_MUX, without forking detection:

// Reads $MYTOOL_MUX and $MYTOOL_MUX_PANE for the fast-path;
// discovery still walks the process ancestry unchanged.
const probe = probeMultiplexer(nodeExec, process.env, { envPrefix: 'MYTOOL_MUX' })

<prefix> names the mux and <prefix>_PANE the pane. This is one prefix per call — the host’s — not an alias list; an unset envPrefix is exactly the default CYBER_MUX behavior.