Review raised whether default-on can be reconciled with the prompt-cache
contract in AGENTS.md, which permits mutating past context only for context
compression and treats per-conversation caching as sacred. It cannot, and the
codebase already says so in its own words.
A micro-compaction pass rewrites already-sent history, so it invalidates the
cached prefix every turn rather than at an episodic boundary. That is the exact
cost the proactive prune gates against: `proactive_prune_min_reclaim_tokens`
exists, per its own config comment, to keep rewrites to "one big episodic break
instead of a tiny break every tool iteration." Micro-compaction has no
equivalent gate -- one exchange per turn means one break per turn, by design.
Default to off. An operator who wants the amortized stall can opt in with
`compression.micro_compact: true` and accept the tradeoff knowingly; nobody
inherits a per-turn cache break from installing an update.
Also register the key in config_defaults so it is discoverable and picked up by
the update path's new-options check -- it was previously read by agent_init but
declared nowhere -- and document the cache cost in docs/micro-compaction.md
instead of only the benefit. The measurements behind the feature (occupancy
plateau, zero batch compactions) never priced cache invalidation, and the doc
now says which numbers a reader would need to measure to justify enabling it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Michael Jordan
d19c182879