Sprint 25 Engineering Log

Program Context

Define the formal Merkle ledger model contracts required for append-only non-repudiation authority.

Implemented model definitions for:

Merkle leaf schema bound to unified execution fingerprint and write-ahead intent lineage.
Strict append-only insertion order with contiguous index enforcement.
Deterministic tree growth rules (left-right pairing, SHA-256, duplicate-last strategy).
Root generation cadence based on fixed leaf intervals.
Root signing procedure contract using control-plane signing authority and canonical JWS payload.
Inclusion proof structure with typed audit path nodes and signature metadata.

Ledger model definitions enforce deterministic hashing and immutable ordering constraints.
Root signing payload contract is canonicalized to prevent signature ambiguity.
Inclusion proof schema fixes verifier-facing structure before implementation in Sprint 27.

Added unit tests covering deterministic leaf hashing, append-order enforcement, cadence behavior, signing payload validation, and inclusion proof constraints.
Added Sprint 25 QA assertions ensuring roadmap checklist and required model contracts are present.

Risk: model parameters may diverge from upcoming runtime implementation.
Mitigation: Sprint 26 must implement against these exact contracts and retain deterministic tests.

Sprint 26 implements append-only Merkle tree runtime and immutable persistence using this model baseline.