Use exact decimal arithmetic for payments, fees, quotes, and limits

[Gozirimdev]

Problem

Financial calculations use JavaScript Number in amount validation, fee calculation, quote conversion, risk scoring, and daily-limit aggregation. Binary floating-point and mixed asset precision can create rounding errors or inconsistent policy decisions.

Outcome

All monetary calculations use explicit decimal arithmetic and asset-specific precision rules from input through settlement and reporting.

Scope

• Select one decimal representation/library and define rounding modes.
• Centralize asset precision and minimum/maximum amount rules.
• Replace Number-based fee, quote, total, and limit calculations.
• Reject values with excessive precision before side effects.
• Define database serialization and API response conventions.
• Reconcile any existing values that violate the new precision policy.

Relevant files

• apps/api/src/utils/validators.js
• apps/api/src/payment/payment.orchestrator.js
• apps/api/src/pricing/pricing.service.js
• apps/api/src/compliance/compliance.service.js
• apps/api/src/wallet/stellar.adapter.js
• apps/api/prisma/schema.prisma

Acceptance criteria

• Calculations are deterministic for XLM, USDC, and configured fiat currencies.
• Values such as 0.1 + 0.2 do not produce binary rounding artifacts.
• Unsupported precision is rejected before a transaction row or Stellar submission.
• Fees and compliance totals use the same rounding policy.
• Boundary, rounding, and high-value cases have automated tests.

[nwosum113-ui]

hello maintainer, i would love to work on this issue

[grantfox-oss]

🦊 GrantFox — @nwosum113-ui has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #154)
2. Your PR will be reviewed by the EF-CHAIN maintainers

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