Government UAP concealment — documented mechanisms (framework)

[FRAMEWORK] The load-bearing honesty distinction for the whole cover-up question: it is DOCUMENTED that governments controlled UAP information via specific mechanisms; it is DISPUTED/ALLEGED that the apparatus conceals recovered non-human technology. Strongest documented PURPOSES are prosaic (protect reconnaissance programs, avoid panic, standard secrecy, Cold-War counter-intel). Organizes existing graph nodes into a tier-tagged taxonomy so 'the machinery of secrecy is real' is not conflated with 'the secret is aliens'. See research_outputs/government-concealment-deepdive.md.