Use existing CLI startup-name options with fixture-owned identities while preserving full uninstall. Add three fixture-free behavioral guards selected by ordinary CI and a teardown wiring contract.

Test-only change. Current-head required local build/tests, bounded review, and hosted fixture teardown passed. No production or workflow changes, and no claim of full shared-host isolation or MXC containment.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>