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Add scripts/macos-install-test.sh, a throwaway-user harness for exercising install.sh the way a brand-new user would on macOS, plus the research note that motivates the approach. The harness has up/run/status/down/deep-reset subcommands. Because install.sh writes only to the user home (pipx venv, ~/.bot-bottle, a PATH line) and never installs the backend, deleting the account is a complete, deterministic reset of the install surface. A disposable macOS VM can't stand in on M1/M2: the Apple `container` backend needs Virtualization.framework, and running it inside a guest VM requires nested virtualization (M3+ only), so a throwaway user is the only way to reach the real host backend from a clean $HOME. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>