Keeps every constraint (explicit run_in_background: false, Agent tool only,
never inline or as a Skill, fallback only after a dispatched subagent fails)
and the reason (fresh-context isolation); drops 'no longer', BACKGROUND/ONLY/
WRONG/FALLBACK caps. test/ship-control-flow.test.ts and
run-in-background-guidance.test.ts check the placeholder and the explicit
flag, not this prose. expected red until the regeneration commit