feat(keyring-api): return raw assets amount

[Kriys94]

Description

This PR adds a new required rawAmount field to the BalanceStruct and FungibleAssetAmountStruct types in the keyring API. This field stores the raw blockchain balance without decimals applied, providing precision for calculations using BigInt/BigNumber.

Motivation

The Problem

When snaps return balance data via keyring_getAccountBalances, the amount field contains the human-readable value with decimals already applied (e.g., "1.5" for 1.5 SOL). However, this causes two issues:

Double division bug: If amount is already normalized ("1.5"), dividing by decimals again produces incorrect values
Precision loss: parseFloat() has limited precision (~15-17 significant digits), causing data loss for large numbers:
parseFloat("1000000000000000001"); // → 1000000000000000000 (last digit lost!)
parseFloat("1000000000000000001"); // → 1000000000000000000 (last digit lost!)

This PR
Add a rawAmount field that stores the exact blockchain value as a string:
{
amount: "1.5", // UI amount (backward compatible)
rawAmount: "1500000000", // Raw blockchain value (precise)
unit: "SOL"
}
{ amount: "1.5", // UI amount (backward compatible) rawAmount: "1500000000", // Raw blockchain value (precise) unit: "SOL"}

This enables:

Backward compatibility: Existing consumers continue using amount
Precision: New consumers use rawAmount with BigInt/BigNumber for exact calculations

Changes

@metamask/keyring-api
BalanceStruct - Used by keyring_getAccountBalances response:

export const BalanceStruct = object({
  amount: StringNumberStruct,   // Human-readable (e.g., "1.5")
  unit: string(),               // Symbol (e.g., "SOL")
  rawAmount: string(),          // NEW: Raw value (e.g., "1500000000")
});

export const BalanceStruct = object({ amount: StringNumberStruct, // Human-readable (e.g., "1.5") unit: string(), // Symbol (e.g., "SOL") rawAmount: string(), // NEW: Raw value (e.g., "1500000000")});

FungibleAssetAmountStruct - Used by AccountBalancesUpdated event and transaction assets:

export const FungibleAssetAmountStruct = object({
  unit: string(),
  amount: StringNumberStruct,
  rawAmount: string(),          // NEW
});

Snap Updates (Solana, Tron, BTC)
Updated getAccountBalances to return both fields:

acc[asset.assetType] = {
  unit: asset.symbol,
  amount: asset.uiAmount,
  rawAmount: asset.rawAmount,  // NEW
};

Breaking Change
This is a breaking change - all snaps implementing keyring_getAccountBalances must now return rawAmount. All snaps have been updated accordingly.

• feat(Asset): return raw assets amount snap-solana-wallet#576
• feat(Asset): return raw assets amount snap-tron-wallet#163
• https://github.com/MetaMask/snap-bitcoin-wallet/pull/573/files

Testing
Updated unit tests for BalanceStruct validation
Updated type definition tests (*.test-d.ts)
Updated mock data in KeyringClient.test.ts and SnapKeyring.test.ts

---

Note

Breaking change: precise balances via rawAmount

• Require rawAmount in Balance and FungibleAssetAmount (balance.ts, asset.ts); keep human-readable amount for compatibility
• Update AssetStruct, transaction fee/participant examples, and docs to include rawAmount; refine comments for clarity
• Enforce rawAmount in AccountBalancesUpdated payloads; adjust validation and type tests (events.test-d.ts, balance.test(-d).ts, asset.test(-d).ts, transaction.test(-d).ts)
• Propagate changes to snap bridge/client tests: balances, fees, and mocked responses now include rawAmount (SnapKeyring.test.ts, KeyringClient.test.ts)
• Changelog notes breaking change and rationale

^{Written by Cursor Bugbot for commit 7b64a6a. This will update automatically on new commits. Configure here.}

[cursor]

rawAmount lacks numeric validation unlike amount field

Medium Severity

The rawAmount field uses string() for validation while amount uses StringNumberStruct which validates the string is numeric. This inconsistency allows non-numeric values like "hello" or "" to pass validation for rawAmount. Since the PR states rawAmount is intended for "calculations using BigInt/BigNumber", invalid non-numeric strings would cause runtime errors when consumers attempt BigInt(rawAmount). Using the same StringNumberStruct (or a stricter integer-only pattern) would provide consistent validation and catch invalid values at the API boundary rather than during calculations.

Additional Locations (1)

• packages/keyring-api/src/api/asset.ts#L32-L33