domain-fintech

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass, no license.

Audit 0.4.1 · source sha f4ff8c82542d · 25 Oct 2026Report an issue or request a re-scan

• Publisherzhanghandong GitHub organizationOwner of the repository this skill is read from
• Source folderzhanghandong/rust-skills/skills/domain-fintechThe exact folder we audited
• LicenceNot declaredAs the repository states it
• Commit pinned for this verdictf4ff8c82542dA new audit runs when the source changes
• Repository statusNot archivedLast push 63 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Use when building fintech apps. Keywords: fintech, trading, decimal, currency, financial, money, transaction, ledger, payment, exchange rate, precision, rounding, accounting, 金融, 交易系统, 货币, 支付

---
name: domain-fintech
description: "Use when building fintech apps. Keywords: fintech, trading, decimal, currency, financial, money, transaction, ledger, payment, exchange rate, precision, rounding, accounting, 金融, 交易系统, 货币, 支付"
user-invocable: false
---

# FinTech Domain

> **Layer 3: Domain Constraints**

## Domain Constraints → Design Implications

| Domain Rule | Design Constraint | Rust Implication |
|-------------|-------------------|------------------|
| Audit trail | Immutable records | Arc<T>, no mutation |
| Precision | No floating point | rust_decimal |
| Consistency | Transaction boundaries | Clear ownership |
| Compliance | Complete logging | Structured tracing |
| Reproducibility | Deterministic execution | No race conditions |

---

## Critical Constraints

### Financial Precision

```
RULE: Never use f64 for money
WHY: Floating point loses precision
RUST: Use rust_decimal::Decimal
```

### Audit Requirements

```
RULE: All transactions must be immutable and traceable
WHY: Regulatory compliance, dispute resolution
RUST: Arc<T> for sharing, event sourcing pattern
```

### Consistency

```
RULE: Money can't disappear or appear
WHY: Double-entry accounting principles
RUST: Transaction types with validated totals
```

---

## Trace Down ↓

From constraints to design (Layer 2):

```
"Need immutable transaction records"
    ↓ m09-domain: Model as Value Objects
    ↓ m01-ownership: Use Arc for shared immutable data

"Need precise decimal math"
    ↓ m05-type-driven: Newtype for Currency/Amount
    ↓ rust_decimal: Use Decimal type

"Need transaction boundaries"
    ↓ m12-lifecycle: RAII for transaction scope
    ↓ m09-domain: Aggregate boundaries
```

---

## Key Crates

| Purpose | Crate |
|---------|-------|
| Decimal math | rust_decimal |
| Date/time | chrono, time |
| UUID | uuid |
| Serialization | serde |
| Validation | validator |

## Design Patterns

| Pattern | Purpose | Implementation |
|---------|---------|----------------|
| Currency newtype | Type safety | `struct Amount(Decimal);` |
| Transaction | Atomic operations | Event sourcing |
| Audit log | Traceability | Structured logging with trace IDs |
| Ledger | Double-entry | Debit/credit balance |

## Code Pattern: Currency Type

```rust
use rust_decimal::Decimal;

#[derive(Clone, Debug, PartialEq)]
pub struct Amount {
    value: Decimal,
    currency: Currency,
}

impl Amount {
    pub fn new(value: Decimal, currency: Currency) -> Self {
        Self { value, currency }
    }

    pub fn add(&self, other: &Amount) -> Result<Amount, CurrencyMismatch> {
        if self.currency != other.currency {
            return Err(CurrencyMismatch);
        }
        Ok(Amount::new(self.value + other.value, self.currency))
    }
}
```

---

## Common Mistakes

| Mistake | Domain Violation | Fix |
|---------|-----------------|-----|
| Using f64 | Precision loss | rust_decimal |
| Mutable transaction | Audit trail broken | Immutable + events |
| String for amount | No validation | Validated newtype |
| Silent overflow | Money disappears | Checked arithmetic |

---

## Trace to Layer 1

| Constraint | Layer 2 Pattern | Layer 1 Implementation |
|------------|-----------------|------------------------|
| Immutable records | Event sourcing | Arc<T>, Clone |
| Transaction scope | Aggregate | Owned children |
| Precision | Value Object | rust_decimal newtype |
| Thread-safe sharing | Shared immutable | Arc (not Rc) |

---

## Related Skills

| When | See |
|------|-----|
| Value Object design | m09-domain |
| Ownership for immutable | m01-ownership |
| Arc for sharing | m02-resource |
| Error handling | m13-domain-error |

Excerpt, first 3,641 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/zhanghandong/rust-skills
git -C rust-skills checkout f4ff8c82542d

Works in

1. 2026-10-25
   ✓SAFE B 89 / 100

   first audit · source f4ff8c82542d

Questions about domain-fintech

• github.com/zhanghandong/rust-skills/tree/main/skills/domain-fint — the audited source at commit f4ff8c82542d and every finding aboveObserved · 25 Oct 2026

Spotted something wrong? Report a correction · Methodology