An audit-grade ledger is a hash-linked, tamper-evident record of every decision and action a system takes, designed to survive adversarial review — an inspector general, a regulator, a forensic audit. Each entry is chained to the previous one, so alteration of any record is detectable by construction.
The distinction from ordinary logging is adversarial durability. Logs serve the operator on a good day; an audit-grade ledger serves the institution on its worst day, when the question is not 'what happened?' but 'prove it.'
Hash-linking means each record incorporates a cryptographic digest of its predecessor: change any historical entry and every subsequent hash breaks visibly. Combined with signatures and timestamps, the ledger becomes evidence rather than testimony.
This vocabulary is implemented, not aspirational — it describes how the MAIA substrate actually runs. See the platform or read the research.