Sprint 26 Engineering Log

Program Context

• Phase: Phase 6
• Sprint: Sprint 26
• Status: Completed
• Primary Architecture Layers: Audit & State Plane, Cryptographic Integrity

Architectural Intent

Implement the append-only Merkle ledger runtime based on Sprint 25 model definitions.

Implementation Detail

Implemented:

• Append-only Merkle tree runtime with deterministic left-right growth and duplicate-last odd node strategy.
• Immutable execution leaf persistence with hash-chained JSONL records.
• Periodic root generation based on fixed leaf cadence.
• Root signing using control-plane signing authority contract.
• Root verification routine that validates both deterministic root recomputation and signature integrity.
• Tamper simulation coverage that detects immutable record mutation.

Security and Control Posture

• Immutable leaf chain prevents silent mutation of persisted evidence.
• Root signing establishes control-plane authority over ledger checkpoints.
• Verification path fails closed on root mismatch or signature mismatch.

QA and Validation Evidence

• Unit tests validate deterministic root behavior, persistence, periodic root cadence, signature verification, and tamper detection.
• Sprint QA test confirms roadmap closure lines and core module contract presence.

Risk Register

• Risk: production authority integration currently relies on abstract signer contract.
• Mitigation: wire Vault transit-backed signer adapter in Sprint 27/28 verifier runtime.

Forward Linkage

Sprint 27 adds inclusion proof API, deterministic rebuild/export, and read-only verifier node workflows.