Registry of each agent's stable prompt prefix in one compressed trie, so feedback loops and multi-agent exchanges send only the diff instead of the full prompt (register, diff, common, stats). Deterministic and local, with a store under ~/.botte. Use when several agents share a large common prefix and the repeated transmission is the cost. Not for deleting sections that nobody uses — use prefix-pruner; not for per-loop windows over a shared context — use context-windows; not for detecting repeated prompts in the logs — use prompt-repetition.
