I architect and maintain modular, zero-dependency, production-grade financial abstractions engineered to eliminate double-charging, guarantee Serializable ACID & Two-Phase Commit (2PC) invariants, enforce PCI-DSS v4.0.1 & OFAC SDN compliance, and orchestrate end-to-end money movement at scale:

 [Inbound Card / Wallet Pay-In]               [Dispute & Risk Shield]
        │                                               │
        ▼                                               ▼
┌──────────────────────┐                       ┌──────────────────────┐
│ 💳 checkout-core     │◄─────────────────────►│ 🛡️ refund-guard      │
│ (TypeScript 100%)    │   Webhook & Dispute   │ (TypeScript 100%)    │
│ • PCI-DSS AES-256    │   State Sync          │ • Chargeback Defense │
│ • 3DS2 & Reg II      │                       │ • Automated Evidence │
│ • Interchange++ & FX │                       │ • Balance Protection │
└──────────┬───────────┘                       └──────────┬───────────┘
           │                                              │
           │         Zero-Sum Double-Entry Posting        │
           └───────────────────┐      ┌───────────────────┘
                               ▼      ▼
                       ┌──────────────────────┐
                       │ 🏛️ ledger-vault      │
                       │ (Go 100%)            │
                       │ • Serializable ACID  │
                       │ • ISO-4217 Precision │
                       │ • SHA-256 Hash-Chain │
                       └──────────┬───────────┘
                                  │
                                  │ Atomic 2PC Settlement & Reserve Holdback
                                  ▼
                       ┌──────────────────────┐
                       │ 💸 payout-engine     │
                       │ (Go 100%)            │
                       │ • OFAC & IRS 1099-K  │
                       │ • FedNow ISO-20022   │
                       │ • NACHA ACH & SEPA   │
                       └──────────────────────┘

Repository	Role & Domain	Runtime	Verification & Compliance	CI Status
💳 checkout-core	Inbound Payment & Acquiring Engine	TypeScript 100%	PCI-DSS v4.0.1, EMV 3DS2, Reg II, ISO-8583, TLA+
💸 payout-engine	Outbound Treasury & Clearing Gateway	Go 100%	OFAC SDN, NACHA ACH, FedNow ISO-20022, IRS 1099-K, TLA+
🛡️ refund-guard	Dispute & Chargeback Defense Middleware	TypeScript	Idempotent Reversals, HMAC Webhooks, Audit Ledgers	Active
🏛️ ledger-vault	Immutable Double-Entry Accounting Core	Go	Serializable ACID, Zero-Sum Invariants, SHA-256 Chain	Active

• 💳 checkout-core — Enterprise Acquiring & Transaction Engine (v1.0.0):
  • PCI-DSS v4.0.1 Cryptographic Isolation: Authenticated AES-256-GCM Primary Account Number (PAN) tokenization vault, ISO/IEC 7812 Luhn validation, and Apple Pay / Google Pay EMV TAVV cryptogram verification.
  • Smart Routing & Conversion Optimization: US Federal Reserve Regulation II (Durbin Amendment) least-cost PINless debit router (STAR, NYCE, PULSE, ACCEL), EMV 3-D Secure 2 (3DS2) PSD2 SCA exemption engine, ISO-8583 hard/soft decline classifier, and multi-gateway Circuit Breakers.
  • Financial Precision & Auditing: Fixed-point BigInt ISO-4217 FX conversion with deterministic Banker's Rounding (Round Half to Even), Interchange++ scheme fee calculator, ISO-20022 (pain.001.001.09) XML credit transfer generator, 3-way settlement reconciliation, and SHA-256 Merkle Tree batch inclusion proofs.
• 💸 payout-engine — Automated Treasury & Multi-Rail Disbursement Gateway (v1.0.0):
  • Atomic 2PC & Marketplace Treasury: Unanimous Two-Phase Commit (2PC) batch coordinator, multi-party Stripe Connect-style split settlement with exact penny-remainder conservation, configurable Rolling Reserve holdbacks, multilateral intraday obligation netting, and Nostro liquidity pool routing.
  • Multi-Rail Clearing & Failover: Real-time US FedNow / TCH RTP (ISO-20022 pacs.008.001.08) XML builder, 94-byte NACHA ACH CCD generator with weighted Modulo-10 ABA routing validation and R01–R29 return code classification, SEPA ISO-13616 Modulo-97 IBAN validator, and automatic rail failover.
  • Pre-Disbursement Regulatory Shield: OFAC SDN sanctions screening, statutory 24% US IRS Form 1099-K backup withholding for unverified TINs, 24-hour beneficiary bank-swap cooling locks (ATO defense), and bounded exponential backoff retry queues with Dead-Letter Queue (DLQ) isolation.
• 🛡️ refund-guard — Idempotent Dispute & Chargeback Management Middleware:
  • Real-time webhook state synchronization, constant-time HMAC-SHA256 signature verification, SHA-256 cryptographic audit ledgers, and automated merchant balance protection against friendly fraud and double-refund race conditions.
• 🏛️ ledger-vault — Immutable Double-Entry Accounting & Reconciliation Engine:
  • Append-only financial ledger enforcing PostgreSQL SERIALIZABLE ACID isolation, strict zero-sum debit/credit invariants ($\sum \text{Debits} - \sum \text{Credits} = 0$), ISO-4217 minor-unit precision, and tamper-evident cryptographic hash-chaining.

• Languages & Runtimes: TypeScript (strict zero-dependency ESM/CommonJS), Go (Golang 1.22+ with concurrency -race verification), PostgreSQL (SERIALIZABLE ACID SQL), TLA+ (Formal Mathematical Specification).
• Payment Protocols & Banking Rails: ISO-20022 (pain.001 & pacs.008), ISO-8583 Acquirer Messaging, US FedNow / RTP, NACHA ACH (94-byte CCD/PPD), SEPA Credit Transfer (ISO-13616 IBAN Mod-97), EMV 3-D Secure 2 (3DS2), Apple Pay / Google Pay Network Tokens (DPAN/TAVV).
• Security, Risk & Regulatory Compliance: PCI-DSS v4.0.1 Envelope Encryption (AES-256-GCM & HMAC-SHA256 Blind Indexing), OFAC SDN Sanctions Screening, US Regulation II Debit Routing, IRS Form 1099-K Backup Withholding, AVS & Sliding-Window Velocity Limiting, SHA-256 Merkle Tree Auditing.
• Distributed Systems & Resiliency: Hybrid Two-Phase Commit (2PC) & LIFO Compensating Sagas, Transactional Outbox Pattern with Jittered Exponential Backoff, Multi-Acquirer Circuit Breakers, Three-Way Settlement Reconciliation.

Building financial-grade infrastructure requires rigorous edge-case testing, formal TLA+ state verification, continuous vulnerability audits, and automated compliance testing against banking clearing specifications.

Your sponsorship directly fuels:

• 🛠️ Maintenance of production-ready, zero-dependency modules for high-reliability payment architectures.
• 🔒 Zero-day security patching, PCI-DSS v4.0.1 / OFAC compliance research, and formal invariant verification.
• ⚡ Continuous integration pipelines and deterministic multi-rail clearing test suites.

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