meridian-storage-evidence

meridian-storage-evidence is the single Python distribution implementing the Meridian V1 evidence Catalog. It provides provider-neutral audit, lineage, provenance, telemetry, policy, query-helper, and low-level OpenTelemetry bridge contracts. It never selects an Adapter, Engine, endpoint, Collector, or deployment topology.

The package is licensed under Apache License 2.0 and targets Python 3.12 or newer. Its released dependencies require meridian-storage-core>=1.1.0,<2 and meridian-storage-semantics>=2.0.1,<3. The exact tested public closure is in requirements-validation.lock; see compatibility.

Install

python -m pip install meridian-storage-evidence==1.0.2

Mapping-first Catalog API

Core discovers EvidenceCatalogProvider through the meridian_storage.catalogs entry-point. Consumer code uses the same mapping-first syntax as every other Meridian Catalog:

evidence = meridian.catalog("evidence")

expression = evidence.append(
    resource="runtime.logs",
    data={
        "severity": "INFO",
        "body": "worker ready",
        "attributes": {"worker": worker_name},
    },
)
meridian.execute(expression)

rows = meridian.execute(
    evidence.query(
        resource="runtime.logs",
        where={"severity": {"eq": "INFO"}},
        limit=50,
    ),
).data

The exhaustive V1 surface is append, create_resource, publish_schema, and query. Audit, lineage, provenance, and telemetry are profiles inside the one evidence Catalog—not additional Catalog names.

Typed helpers and operation hooks

Mapping inputs remain authoritative. Typed records add validation and deterministic serialization:

from datetime import UTC, datetime

from meridian_storage.evidence import EvidenceMetadata, LogRecord

record = LogRecord(
    severity="INFO",
    body="worker ready",
    metadata=EvidenceMetadata(
        event_time=datetime.now(UTC),
        observed_time=datetime.now(UTC),
        tenant="tenant-a",
        scope={"environment": "production"},
    ),
)
expression = evidence.append(resource="runtime.logs", data=record)

OperationEvidenceHooks builds explicit append plans from Core Operation, OperationContext, OperationResult, and normalized failures. It propagates request, execution, tenant, scope, trace, and safe Adapter provenance without copying unrestricted request/response bodies. Required atomic audit plans must pass EvidenceHookPlan.validate_atomic_resolution before publication or startup.

OpenTelemetry boundary

OTelEvidenceBridge preserves OTel log, span, and metric fields and supplies a bounded queue, timeouts, recursion suppression, and non-recursive health counters. The separate public meridian-storage-plugin-observability package owns consumer-facing tracers, meters, structured loggers, exporter wiring, and process-wide provider installation. Core deliberately has no Meridian.telemetry() method.

Policy and retention

EvidencePolicy handles required fields, deterministic redaction/drop/rejection, record and attribute bounds, distinct-value cardinality budgets, access-scope inputs, atomicity, queue-failure policy, and logical retention intent. RetentionPolicyInput does not configure storage, delete Data, enable WORM, or implement a military/national-security profile. Those remain deployment and future-profile concerns.

Architecture boundary

Meridian has exactly five Catalogs: structured, object, cache, evidence, and streaming. Evidence persistence belongs to independently released Adapters. Collector deployment, OTLP routing, storage placement, retention execution, recovery, and lifecycle belong to MeridianConstructs and deployment IaC. Public values contain logical Resource references only; they never expose provider credentials, endpoints, or physical names.

The implementation authority is Meridian HLD revision 60 and Meridian Catalogs and Public Interfaces revision 72, section 5.7. See architecture, contracts, and compatibility.

Development

python -m pip install '.[test]'
ruff format --check src tests scripts
ruff check src tests scripts
mypy src
python scripts/verify_contracts.py
pytest --cov=meridian_storage.evidence --cov-report=term-missing
python -m build --no-isolation
python scripts/verify_artifacts.py dist

Release builds are made twice under one SOURCE_DATE_EPOCH, compared byte-for-byte, verified, described by a deterministic SPDX 2.3 SBOM, and attested by GitHub Actions.