Orbit: brain assumes a GNU/Linux userland on macOS (`timeout` and other coreutils missing)

_Context: from a controlled experiment in which eight frontier models (opus, sonnet, gpt, gpt2, gemini-2.5-pro, gemini-3.5-flash, deepseek, haiku) each drove an Orbit session to reanalyze the same RNA-seq dataset (Santana 2023 *C. auris*) on 2026-06-02–04. Evidence quotes are from the per-run `activity.jsonl` logs._

## Problem

On macOS the brain reaches for GNU coreutils that aren't present in the default `zsh`/BSD userland, and the failing command blocks recovery.

## Evidence

- **haiku**: `/bin/bash: line 7: timeout: command not found` — this was the agent's last recovery attempt during a history-copy retry, so the failure left the session dead with an empty notebook.

## Impact

Medium. macOS is a primary Orbit target; assuming `timeout`/`gtimeout`/GNU flags silently breaks shell fallbacks.

## Proposed direction

OS-aware command selection (detect Darwin, prefer portable equivalents or `gtimeout` if present), or a small set of portable helper wrappers the brain is told to use instead of GNU-only commands.