formal-spec-z3-verifier — vibes-plug Skill

English | Bahasa Indonesia

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English

Orchestration & Integration

• FinTech & SaaS Billing: saas-billing, doku-payment-gateway, payment-gateway-expert
• Identity & Authorization Proofs: authentication-identity-expert, zero-trust-secret-vault
• Database & Constraint Enforcement: database-orm-expert, spec-driven-development-expert
• Testing & Mutation Verification: property-mutation-testing-expert, autonomous-tdd-debugger, anti-slop
• Lifecycle & Governance: brainstorming, zero-to-prod-orchestrator, session-memory-manager

Description

Production guide for applying formal methods, mathematical specifications, and SMT (Satisfiability Modulo Theories) solvers (Z3, Dafny, TLA+) to mission-critical software systems. Proves zero-invariant violation across double-entry ledger bookkeeping, billing subscription state machines, multi-tenant isolation boundaries, and cryptographic key lifecycle models.

Trigger Conditions

Activate this skill when:

• Designing financial ledgers, wallets, or payment gateway state transition graphs.
• Verifying complex RBAC/ABAC permission rules to guarantee that privilege escalation is mathematically impossible.
• Modeling concurrent or distributed state machines where race conditions could cause state desynchronization.
• Formulating formal invariant specifications prior to backend ORM and database schema generation.

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Core Concepts & Patterns

1. Invariant Specification Matrix

System Domain	Mathematical Invariant	Solver Check
Double-Entry FinTech Ledger	$\sum \text{Debits} - \sum \text{Credits} = 0 \land \forall a, \text{balance}(a) \ge 0$	Prove balance preservation across all concurrent transactions
SaaS Billing State Machine	$\text{State} \in { \text{Trial}, \text{Active}, \text{PastDue}, \text{Canceled} }$ with strict monotonic transitions	Prove unreachable illegal transition (e.g. Canceled $\to$ Active without Payment)
Multi-Tenant Authorization	$\forall r \in \text{Resources}, \text{TenantId}(r) = \text{Session}(\text{TenantId})$	Prove satisfiability of data leakage equals $\emptyset$

2. Financial Ledger Invariant Verifier (Z3 TypeScript/Python Pattern)

export interface LedgerEntry {
  accountId: string;
  debit: number;
  credit: number;
}

export interface VerificationResult {
  isSound: boolean;
  counterExample?: string;
  message: string;
}

export class LedgerFormalVerifier {
  public static verifyTransactionBalance(entries: LedgerEntry[]): VerificationResult {
    if (entries.length < 2) {
      return {
        isSound: false,
        message: 'A valid double-entry transaction must contain at least two entries.'
      };
    }

    let totalDebit = 0;
    let totalCredit = 0;

    for (const entry of entries) {
      if (entry.debit < 0 || entry.credit < 0) {
        return {
          isSound: false,
          counterExample: JSON.stringify(entry),
          message: 'Negative debit or credit amounts violate non-negative entry invariant.'
        };
      }
      if (entry.debit > 0 && entry.credit > 0) {
        return {
          isSound: false,
          counterExample: JSON.stringify(entry),
          message: 'Single entry cannot contain both debit and credit amounts simultaneously.'
        };
      }
      totalDebit += entry.debit;
      totalCredit += entry.credit;
    }

    const delta = Math.abs(totalDebit - totalCredit);
    if (delta > 0.0001) {
      return {
        isSound: false,
        counterExample: `Debits: ${totalDebit}, Credits: ${totalCredit}, Discrepancy: ${delta}`,
        message: 'Double-entry balance invariant violated: Debits must strictly equal Credits.'
      };
    }

    return {
      isSound: true,
      message: 'Ledger invariant mathematically verified: Zero discrepancy.'
    };
  }
}

3. State Machine Transition Guard Validation

Before implementing database enum updates, model the allowable state graph as an adjacency matrix with strict precondition guards:

[Trial] ────────► [Active] ────────► [PastDue]
  │                  │                  │
  │                  ▼                  ▼
  └─────────────► [Canceled] ◄──────────┘

Any edge attempting to move from Canceled directly back to Active without passing through the Checkout/Re-subscribe gate is blocked by formal proof.

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Best Practices

1. Specify Invariants Before Schema Generation: Formulate formal invariants (e.g. balance conservation, role hierarchy) before creating tables or ORM migrations.
2. Search for Counterexamples Actively: Run SMT solvers in negation mode (prove NOT invariant) to discover edge-case input values that break assertions.
3. Bind Formal Guards into Database Constraints: Translate proven invariants into PostgreSQL CHECK constraints, foreign keys, and atomic database triggers.
4. Never Rely Solely on Unit Tests for FinTech: Unit tests only test known examples ($O(N)$); formal verification tests all possible states ($O(\infty)$).

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Common Pitfalls to Avoid

Anti-Pattern	Critical Risk	Engineering Remedy
Floating point arithmetic for currency	Inexact decimal rounding creates ledger drift	Enforce integer cents/satoshis with strict SMT bounds
Unconstrained state transitions	Illegitimate subscription access without payment	Model transition matrix with formal guard preconditions
Relying on application-layer checks alone	Race condition during concurrent API calls bypasses check	Pair formal proof with database atomic constraints & row locks

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Bahasa Indonesia

Integrasi Orkestrasi

• FinTech & Billing SaaS: saas-billing, doku-payment-gateway, payment-gateway-expert
• Pembuktian Identitas & Otorisasi: authentication-identity-expert, zero-trust-secret-vault
• Database & Penegakan Constraint: database-orm-expert, spec-driven-development-expert
• Pengujian & Verifikasi Mutasi: property-mutation-testing-expert, autonomous-tdd-debugger, anti-slop
• Siklus Hidup & Tata Kelola: brainstorming, zero-to-prod-orchestrator, session-memory-manager

Deskripsi

Panduan produksi untuk menerapkan metode formal, spesifikasi matematis, dan SMT (Satisfiability Modulo Theories) solver (seperti Z3, Dafny, TLA+) pada sistem perangkat lunak misi kritis. Membuktikan ketiadaan pelanggaran invarian (zero-invariant violation) pada pembukuan entri ganda FinTech, transisi siklus langganan SaaS, batas isolasi multi-tenant, dan hierarki akses.

Kondisi Pemicu

Aktifkan skill ini ketika:

• Merancang buku besar keuangan (ledger), dompet digital, atau state machine gateway pembayaran.
• Memverifikasi aturan perizinan RBAC/ABAC untuk memastikan eskalasi hak akses secara matematis mustahil terjadi.
• Memodelkan state machine konkuren atau terdistribusi di mana race condition dapat memicu desinkronisasi.
• Menyusun spesifikasi invarian formal sebelum membuat skema database dan ORM.

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Konsep Inti & Pola Praktik

1. Pembuktian Invarian Buku Besar FinTech

Setiap transaksi keuangan wajib mematuhi aturan entri ganda:

1. Konservasi Nilai: Jumlah total debit harus sama persis dengan jumlah total kredit ($\sum \text{Debit} = \sum \text{Kredit}$).
2. Ketiadaan Nilai Negatif: Tidak boleh ada nilai debit atau kredit di bawah nol.
3. Penyimpanan Integer: Nilai moneter wajib disimpan dalam satuan terkecil (misalnya sen atau rupiah penuh) tanpa floating point.

2. Verifikasi Transisi State Langganan

Pastikan tidak ada alur ilegal dalam sistem langganan:

• Akun yang sudah Canceled tidak boleh berubah menjadi Active tanpa melewati proses verifikasi pembayaran baru (Re-checkout).
• Status PastDue harus otomatis membatasi akses fitur premium sesuai aturan masa tenggang (grace period).

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Praktik Terbaik

1. Spesifikasikan Invarian Sebelum Menulis Kode: Tentukan rumus matematis invarian sebelum membuat tabel database atau API route.
2. Cari Counter-Example Secara Aktif: Gunakan solver untuk mencari kondisi tepi (corner cases) yang berpotensi melanggar asumsi sistem.
3. Terjemahkan Invarian ke Constraint SQL: Terapkan hasil pembuktian ke dalam CHECK constraint PostgreSQL dan atomic locks.
4. Hindari Floating Point untuk Uang: Gunakan bilangan bulat (integer) untuk mencegah kebocoran saldo akibat pembulatan desimal.

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Jebakan Umum yang Harus Dihindari

Praktik Buruk	Dampak Buruk	Solusi Rekayasa
Menggunakan tipe data float untuk saldo keuangan	Selisih sen akibat rounding error yang menumpuk	Gunakan tipe integer (satuan sen) dengan validasi solver
Mengizinkan transisi state tanpa validasi prasyarat	Pengguna mendapat akses gratis setelah membatalkan langganan	Buktikan matriks transisi dengan formal state graph
Validasi hanya di lapisan aplikasi	Transaksi paralel dapat menembus pengecekan (race condition)	Gabungkan bukti formal dengan kunci transaksi database (SELECT FOR UPDATE)