read-only-instrumentslisted

# Read-Only Instruments An **instrument** — in the aviation-panel sense: a gauge you read, not a control you pull — is a read-only aggregate reading over stored state: a distribution, composition tally, or cluster structure, built so the operator can choose interventions from data instead of intuition. Worked example: an agent that accumulates a text corpus ships a module reporting supply per consumed view and pairwise-cosine diversity over the pool — an echo-chamber detector the operator reads before deciding whether to rebalance the corpus. **Not the same thing as an audit log.** An audit log records one event per decision for offline replay ([`replayable-audit-logs`](../replayable-audit-logs/SKILL.md)). An instrument reads across the whole store at query time. They compose: the log is the corpus, the instrument is one lens over it. ## When to build one (instrument-first sequencing) - **Before intervening.** Quantify current state → choose the intervention from readings → re-measure. There is an extra reason worth checking every time: if a confounder is in play (say, an embedding or generation model was swapped days earlier), any uninstrumented change becomes unattributable — you cannot tell your intervention's effect from the confounder's. - **When a floor/threshold would otherwise be guessed.** A rescue-lane floor, a similarity cutoff, a cap — pick it from the measured distribution, never as a bare number invented at the keyboard. - **When an open observat