Ledger: threshold signing, CRDT merge, and coordinator quorum

[jeremymanning]

Description

The ledger module has entry definitions, CRDT structure, and transparency anchoring, but the full multi-coordinator operation needs:

• Threshold signing with t-of-n coordinator signatures (currently single-node stub)
• CRDT OR-Map merge across coordinator replicas
• Cross-shard MerkleRoot computation every 10 minutes
• Donor-facing balance verification (worldcompute donor credits --verify)

Requirements

• Implement t-of-n threshold signing (target: 3-of-5 for initial coordinator set)
• CRDT OR-Map: merge function, conflict resolution, eventual consistency
• MerkleRoot computation across all coordinator log heads
• Local O(log n) balance verification for donors
• Ledger replication via GossipSub
• RS(10,18) durability for ledger data

Success Criteria

• Threshold signing works with 3-of-5 coordinator quorum
• CRDT merge produces consistent state across replicas
• MerkleRoot anchored to Rekor every 10 minutes
• credits --verify performs local cryptographic verification
• Integration test: multi-coordinator ledger operations
• cargo test passes

Testing (Principle V)

• 5 coordinator nodes → sign entry → verify 3-of-5 threshold
• Partition coordinators → rejoin → verify CRDT merge consistency
• Verify MerkleRoot appears in Rekor within 10 minutes
• Run credits --verify → verify proof validates against published root

[jeremymanning]

Partially addressed by spec 004 / PR #59 — not closing. BLS threshold signing (threshold_crypto), CRDT OR-Map merge, MerkleRoot computation, verify_balance all real. HOWEVER, the cross-shard anchor to Rekor uses the all-zero placeholder key (see #29).

Remaining work tracked here.

[jeremymanning]

Spec 005 progress — PR #61

STATUS: Indirectly addressed via real Rekor P-256 fix (issue #29).

Ledger "cross-shard anchor to Rekor" per the original issue description now goes through real ECDSA P-256 signature verification instead of the [0u8; 32] Ed25519-assumed bypass. See #29 for details of the Rekor key-algorithm correctness fix.

BLS threshold signing, CRDT merge, MerkleRoot, and verify_balance logic from spec 004 unchanged.

See notes/session-2026-04-19-spec-005-kickoff.md.