v1.6.13

Added

• Legion::Data::AuditRecord — tamper-evident audit record primitive with SHA-256 hash chain (closes #7)
  • append(chain_id:, content_type:, content_hash:, metadata: {}, sign: false) — inserts a new record, linking it to the previous tail via parent_hash and chain_hash
  • verify(chain_id:) — walks the chain and re-derives every hash, returning { valid:, length: } or { valid: false, broken_at:, reason: } on tampering
  • walk(chain_id:, since: nil, limit: 1000) — return deserialized records in chronological order
  • query_by_type(content_type:, since: nil, limit: 100) — cross-chain query by content_type
  • compute_chain_hash(parent_hash, content_hash, timestamp, content_type) — public for independent verification
  • Multiple independent chains share a single audit_records table, keyed by chain_id
  • Chain hash formula: SHA256("parent_hash:content_hash:unix_ns:content_type") — timezone-independent via nanosecond epoch
  • Optional signing via Legion::Crypt.sign when sign: true; signature column is nil when signing is unavailable
• Migration 058: audit_records table with chain_id, content_type, content_hash, parent_hash, chain_hash (unique), signature, metadata, created_at; PostgreSQL NO UPDATE/DELETE rules for DB-level append-only enforcement
• Legion::Data::Model::AuditRecord — Sequel model with before_update/before_destroy immutability guards and parsed_metadata helper
• 29 new specs covering constant, hash computation, DB-unavailable guards, chain creation, chain verification, tamper detection, walk/query operations, and model immutability