Plugins shelling out to bare `hermes` via the terminal tool hit
`command not found` (exit 127) when the gateway was launched without the
hermes install dir on PATH (systemd, service managers, cron, desktop
launchers) — even though `hermes` works in the user's own interactive
terminal, which sources the shell rc that exports that dir.
The terminal tool's subshell PATH was the agent process PATH plus a
static set of system dirs (_SANE_PATH); it never included wherever the
hermes console-script actually lives (~/.local/bin, the venv bin/Scripts,
pipx, nix). Resolve that dir once (which/argv0/sys.executable) and
prepend-if-missing it so bare `hermes` resolves regardless of launch
method.
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