Nested redaction idempotence¶

openmed.risk.idempotence checks whether a structured redaction result is stable when the result is processed a second time. It is a deterministic, local review aid, not a FHIR or OMOP conformance check, a compliance certification, or a clinical decision guarantee.

Compare two passes¶

Passes may be nested JSON mappings, local JSON files, or result objects with a resource/data/output attribute and a report. Report metadata can contain aggregate counts, a policy or policy_fingerprint, and redaction events:

from openmed.risk import check_idempotence

first = {
    "resource": {
        "resourceType": "Bundle",
        "entry": [{"resource": {"resourceType": "Patient", "id": "synthetic-a"}}],
    },
    "report": {
        "policy_fingerprint": "sha256:" + "a" * 64,
        "counts": {"redacted": 1},
        "redactions": [
            {
                "path": "entry[0].resource.id",
                "action": "replace",
                "surrogate": "[SYNTHETIC-ID]",
            }
        ],
    },
}

second = first  # The second pass has the same synthetic evidence.
result = check_idempotence(first, second)
assert result.is_idempotent

The result compares nested shape, aggregate counts, action counts and paths, surrogate fingerprints, and global or event-level policy fingerprints. A non-idempotent result exposes non_idempotent_paths and structured differences grouped by dimension. Scalar changes are detected even when neither pass includes redaction-event metadata.

Bounded inputs¶

The checker rejects cyclic values, ambiguous wrapper or metadata aliases, duplicate JSON object keys, non-finite numbers, and unsupported scalar types. It also applies fixed limits to file size, nesting depth, container size, total nodes, text and key lengths, metadata sources, and redaction events. Rejections raise IdempotenceInputError with a closed error message that does not include input values or exceptions raised by custom containers.

Privacy properties¶

Reports include schema paths, scalar kinds, array lengths, counts, safe action names, and SHA-256 fingerprints only. Source values, replacement values, and unknown schema keys, action names, or policy names are not copied into JSON, Markdown, repr, or exceptions. Unknown keys and identifiers are represented by SHA-256 fingerprints. Surrogate fingerprints are equality evidence, not a claim of cryptographic anonymization. The checker accepts only in-memory or local JSON inputs and makes no mandatory network call.

Fixtures for FHIR-shaped resources and OMOP-shaped tables should remain synthetic and offline. The checker does not validate clinical semantics or replace a formal privacy review.