agent-signals

070. psmux starts each pane with a long pwsh command that defines a claude function

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Date
2026-10-31
Agents
Claude Code, Antigravity CLI
Measured on
real machine

Measured

2026-10-31, psmux with tmux 3.4.0 from Chocolatey (C:\ProgramData\chocolatey\bin\psmux.exe and tmux.exe), PowerShell 7.6.7, Antigravity CLI (agy) 1.4.12 and Claude Code 2.1.314, on Windows 11 Pro 10.0.26300 (x64). The probe kit (probes/run.ps1) read the processes with CIM (Win32_Process): the name, the parent, the start time and the command line. Measured on: real machine.

What was measured

  1. Two psmux servers ran, each as tmux.exe. Each pane was a pwsh.exe child of a tmux.exe. Six pane shells ran.
  2. The command line of each pane shell was about 4 KB: pwsh.exe -NoLogo -NoProfile -NoExit -Command "<script>". The script:
    • sets PSReadLine options, and the history file from PSMUX_PSREADLINE_HISTORY;
    • loads the PowerShell profiles by hand, because of -NoProfile;
    • replaces Set-Location, Push-Location and Pop-Location, so that the process folder follows the shell folder;
    • defines a function env that runs a command with variables, in the form of the Unix env;
    • when PSMUX_CLAUDE_TEAMMATE_MODE is set, defines a function claude that adds --teammate-mode $env:PSMUX_CLAUDE_TEAMMATE_MODE, unless the settings of Claude Code already set teammateMode.
  3. An agy process ran as tmux.exe > pwsh.exe > agy.exe.
  4. The Claude probe matched the six pane shells as Claude processes, because their command line holds the word claude. They had no pid file. The two real Claude processes ran as idea64.exe > pwsh.exe > claude.exe, in the terminal of IntelliJ IDEA, not in psmux.
  5. psmux ls and tmux ls gave the same session list: one session with one window and one pane.

Mechanism

psmux runs the pane shell with -NoProfile and its own start script. The claude function exists only in a psmux pane where the variable is set. A user who types claude there starts claude.exe with an extra flag, so the command line of the agent differs from the command line that the user typed.

A reader that finds agent processes by a word in the command line also finds psmux pane shells. It must match the program name, claude.exe.

Incident

The kit printed the six command lines in full, 24 KB in total. The probe fix matches on the program name and cuts each command line.

Screens

None.

Not measured