t2000-financial-amounts

Financial Amount + Token Data Safety

CLAUDE.md rules 6 and the constants section state the invariants. This is the detail.

Floor display amounts — never round up

Any amount shown to users or passed to an SDK transaction builder must be ≤ the actual on-chain balance. Math.round can round up, producing more raw units than the user holds → "Insufficient balance".

// ❌ BAD — Math.round(1.1286 * 100) / 100 = 1.13 (more than on-chain!)
const amount = Math.round(rawAmount * 100) / 100;

// ✅ GOOD — Math.floor always produces amount <= actual
const amount = Math.floor(rawAmount * 10000) / 10000;

Token decimal precision

Floor to the token's on-chain decimals, capped at 8:

Token	On-chain decimals	Display floor
SUI	9	4 dp
USDC	6	2 dp
GOLD (XAUM)	9	8 dp
anything else	—	Math.min(decimals, 8) dp

Never hardcode these at a call site — read them from the registry (below).

SDK transaction amounts

Any SDK builder taking an amount converts via amount * 10^decimals. A display amount that was rounded UP produces more raw units than the user has → the tx fails. The live write surface is send · swap · pay; the floor-not-round rule applies to every one of them.

Preset amounts for chip flows

For assets with tiny balances (< 0.01), use dynamic precision:

const dp = held >= 1 ? 100 : held >= 0.01 ? 10000 : 100000000;
const preset = Math.floor(held * fraction * dp) / dp;

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Token data — canonical sources

Data	Export	Location
Swap-supported names → coin types	TOKEN_MAP	packages/sdk/src/token-registry.ts (derived from COIN_REGISTRY)
Token metadata (coin types, decimals, symbols)	SUPPORTED_ASSETS	packages/sdk/src/constants.ts
Resolvers (resolveSymbol, resolveTokenType, getDecimalsForCoinType)	COIN_REGISTRY	packages/sdk/src/token-registry.ts

Rules

1. Never create a new token map. Import from the canonical source above.
2. Adding a token = update TOKEN_MAP in the SDK. Everything downstream (system prompt, swap resolution) derives from it automatically.
3. Decimals are registry data, not call-site literals. USDSUI, USDe, suiUSDT are all 6 decimals — encoded in COIN_REGISTRY / SUPPORTED_ASSETS.
4. Frontend token lists import from the SDK registry; don't duplicate coin-type maps outside the canonical files.