007 provenance hash chain

007_provenance_hash_chain (completed for v0.1)

Goal

Add tamper-evident provenance to the ledger.

What shipped

• src/abstractruntime/storage/ledger_chain.py
• HashChainedLedgerStore
• verify_ledger_chain(records)
• StepRecord includes optional fields:
• prev_hash, record_hash, signature

Notes

• This provides tamper-evidence, not non-forgeability.
• Signatures are planned as an optional extra.

Related ADRs

• ADR 0003: Provenance Hash Chain — Why hash chain first, signatures later

Next Steps

• 008_signatures_and_keys.md — Cryptographic signatures (planned)