DefaultVerifier MCP — Phase A

Agent-native MCP server for DefaultVerifier. Phase A starts with verification, not emission.

What this is

An MCP server that exposes DefaultVerifier's verification surface to AI agents. It verifies signed SAR v0.1 settlement receipts locally — offline, no network required.

Doctrine:

Capability ≠ Authority
Authority ≠ Execution
Execution ≠ Verification
Verification must leave evidence

Phase A tools

verify_receipt

Verify a signed SAR v0.1 receipt locally.

• Offline — no network calls
• Canonicalizes using RFC 8785 / JCS
• Verifies Ed25519 signature against bundled public key registry
• Returns typed result with status (tool outcome) and verdict (issuer's signed outcome)

Key semantics:

• status=PASS means the signature and digest are cryptographically valid
• verdict is the issuer-signed outcome from the receipt itself (PASS/FAIL/INDETERMINATE)
• A valid FAIL receipt returns { status:"PASS", verdict:"FAIL" }
• A tampered receipt returns { status:"INVALID" }

get_verification_log

Return entries from DefaultVerifier's local verification log (/var/www/html/verified.json).

• Local file only in Phase A
• Preserves the file's disclaimer and non-endorsement language
• Does not add endorsement language

Boundaries (what DefaultVerifier does NOT claim)

• Does not prove payment finality
• Does not prove legal settlement finality
• Does not execute tasks
• Does not approve actions
• Does not release or custody funds
• Does not imply partnership, endorsement, or official integration
• Does not issue TrustScores

How to run

npm install
npm test       # run self-tests (requires all tests to pass before commit)
npm start      # starts on 127.0.0.1:3013 (dev only — do not deploy directly)

Health check: curl http://127.0.0.1:3013/healthz

MCP endpoint: http://127.0.0.1:3013/mcp

Local-first design

verify_receipt requires no network. It uses:

• keys/sar-keys.json — bundled public key registry (kid-01, kid-02, kid-03)
• Node.js built-in crypto for Ed25519 verification
• canonicalize npm package (RFC 8785/JCS) for byte-for-byte parity with the Python verifier

Key registry

Includes three production keys:

• sar-prod-ed25519-01 — original key
• sar-prod-ed25519-02 — rotation 2
• sar-prod-ed25519-03 — current key (used by recent receipts)

Fixtures

File	Expected result
sar-v0.1-pass.json	status PASS, verdict PASS
sar-v0.1-fail.json	status PASS, verdict FAIL
sar-v0.1-indeterminate.json	status PASS, verdict INDETERMINATE
sar-v0.1-current-kid03.json	status PASS, kid sar-prod-ed25519-03
tampered-receipt.json	status INVALID

Future phases

• Phase B: resolve_receipt — resolve a receipt_id to its canonical source
• Phase C: resolve_chain — follow a receipt chain
• Phase D: check_issuer — issuer registry lookup
• Phase E: emit_receipt_optional — optional emission surface
• Phase F: TrustProfile

Port assignment

Dev port: 127.0.0.1:3013 (not proxied — do not expose without nginx config review)

Production settlement-witness-mcp remains on port 3003 and is not modified by this repo.