UDIL Evidence Ledger API.

This header defines the public API for the UDIL evidence ledger subsystem. The ledger implements a local, append only, cryptographically verifiable logging structure intended for audit, non-repudiation, and regulatory evidence purposes.

The UDIL ledger is designed as a foundational substrate for higher-level systems, including secure financial messaging, asset transfer workflows, and globally anchored provenance systems. It is not a consensus blockchain and does not perform settlement, balance tracking, or global ordering.

Core properties provided by this API include:

• Append only record storage with hash chaining
• Deterministic record commitments using Keccak-based hashing
• Cryptographic signatures over records and checkpoints using UDIF keys
• Merkle tree batching and checkpointing for scalable audit
• Inclusion proofs for selective disclosure and sampled verification
• External anchoring references for third-party attestation
• Explicit epoch management for key rotation and administrative resets

Records stored in the ledger are opaque to the ledger itself. The ledger does not interpret message semantics, payload formats, or application-level meaning. Its sole responsibility is to provide verifiable evidence of existence, ordering, and authorization.

Typical usage flow:

1. Initialize a ledger instance with a stable ledger identifier, epoch, signing key, and append-only storage backend.
2. Append records representing messages, acknowledgments, or administrative actions, each producing a signed record commitment.
3. Periodically batch records into checkpoints, producing signed Merkle roots that summarize ledger state over a sequence range.
4. Optionally anchor checkpoint commitments to an external witness system.
5. Provide inclusion proofs and checkpoint artifacts to auditors, counterparties, or regulators as required.

All cryptographic operations are domain separated and deterministic. Verification of records and checkpoints can be performed independently by third parties without access to private keys or plaintext payloads.

This API is intended to be stable and forward compatible. Extensions such as global provenance pillars, cross-ledger anchoring, or asset-level semantics can be layered above this interface without breaking existing evidence guarantees.