GPT review F1: prepare() built the host env from HOME, PATH, TMPDIR,
MOSAIC_CONFIG and NODE_EXTRA_CA_CERTS only, so the pi credential preflight
refused the assistant launch (no-session-credential) and the RESULT wait
failed. scripts/test-federation-acceptance.sh red on 6e9f3d723, green with
the fake ZAI_API_KEY the cli tests use.