Belief Ledger

The belief ledger is the diff-tracking layer on top of Arkeus memory. Every time a fact changes class — from inferred to asserted, from asserted to false, from temporary to expired — the ledger records the transition, the cause, and the downstream beliefs that depended on it.

This exists because retraction is the hardest part of memory. Adding a fact is easy. Realizing a fact was wrong and cleanly pulling back everything that got built on top of it is not. In a system without a ledger, the old belief becomes invisible background truth. Agents keep acting as if it were still valid. The correction never reaches the places it needed to reach.

The ledger solves this with two pieces: inline frontmatter on every fact (class, source, last_verified, ttl) and an append-only log at logs/belief_ledger.md that tracks the state changes. When a fact transitions to false or expired, the executor walks the ledger to find what depended on it and flags those artifacts for re-review.

The distinction matters: inline frontmatter tells you what we believe now. The ledger tells you how we came to believe it and what else is loadbearing on it. Without both, you can patch the current state but not the historical derivation chain, which means silent drift becomes possible again.

The ledger is also where observability of absence lives. When a fact is unknown — not just missing, but deliberately marked as unknown — the ledger knows and can surface that gap when it becomes relevant. This is what separates a memory system from a database.