fix(display): negative token amounts render as "-1.-5 ETH" due to BigInt modulo sign propagation

[Sertug17]

Bug Report

While testing the vibenet explorer and TIPS transaction list with edge-case token amounts, we noticed that negative values display incorrectly in the UI.

Affected files

• app/vibenet/library/explorer.ts → fmtTokenAmount
• app/tips/library/explorer-format.ts → formatUnits

Reproduction

fmtTokenAmount(-1_500_000_000_000_000_000n, 18)
// Expected: "-1.5"
// Actual:   "-1.-5"

fmtTokenAmount(-500_000_000_000_000_000n, 18)
// Expected: "-0.5"
// Actual:   "0.-5"

Root cause

JavaScript's BigInt % operator preserves the sign of the dividend, not the divisor. So when raw is negative, frac = raw % divisor is also negative and frac.toString() produces a string starting with "-", which gets concatenated directly into the fractional part:

const frac = raw % divisor;          // -500_000_000_000_000_000n (negative!)
const fracStr = frac.toString()       // "-5"
  .padStart(decimals, '0')
  .replace(/0+$/, '');
return `${whole.toLocaleString()}.${fracStr}`; // "0.-5"

Fix

Take the absolute value of frac before formatting:

const whole = raw / divisor;
const frac = (raw % divisor + divisor) % divisor; // always positive

Or more explicitly:

const frac = raw < 0n ? -(raw % divisor) : raw % divisor;

Same fix applies to formatUnits in explorer-format.ts.

Notes

• All 131 existing vitest tests pass negative BigInt inputs are not currently covered by any test
• Positive amounts and zero are unaffected
• fmtHexInt has a separate but related issue: it uses Number.parseInt(hex, 16) which silently loses precision for values above 2^53. Should use BigInt(hex) instead.