fix(assets-controller): avoid recomputing getStateForTransactionPay on every transaction state change

[Kureev]

Explanation

formatStateForTransactionPay converts the full AssetsController state into the legacy five-controller shape for transaction-pay-controller, running toChecksumAddress (keccak256) for every asset and parseCaipAssetType for every asset ID on every call. It is exposed as the AssetsController:getStateForTransactionPay messenger action, which transaction-pay-controller invokes on every TransactionController:stateChange — many times during a single transaction approval, and at least twice per event through messenger delegation — while its inputs only change when the assets pipeline updates.

In a CPU profile of MetaMask Mobile (RC) captured while triggering a transaction approval in the MetaMask Pay deposit flow, keccak256 via toChecksumAddress accounted for 10.4% of all samples (~23% of active CPU), the single largest active bucket, with GC pauses (4.1%) as a symptom of the per-event object churn. See #9545 for the full breakdown.

This change memoizes the last result on input identity: the assetsBalance / assetsInfo / assetsPrice state slices and networkConfigurationsByChainId are compared by reference (BaseController state updates are immutable, so unchanged slices retain identity), selectedCurrency by value, and the per-call-rebuilt accounts array and nativeAssetIdentifiers record element-wise. Repeat calls with unchanged inputs return the cached object; any real input change recomputes. The conversion body is unchanged, moved to an internal computeStateForTransactionPay.

MetaMask Mobile currently carries this fix as a Yarn patch (MetaMask/metamask-mobile#33466), which can be dropped once this lands and a release is picked up.

References

• Fixes formatStateForTransactionPay runs keccak256 per asset on every TransactionController:stateChange #9545
• Mobile-side mitigation: fix(money): memoize assets-controller getStateForTransactionPay (MUSD-1180) metamask-mobile#33466

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

---

Note

Low Risk
Performance-only change with identical output when inputs change; single-entry module cache is appropriate for the hot path but assumes callers pass stable slice references as today.

Overview
formatStateForTransactionPay (used by AssetsController:getStateForTransactionPay) now memoizes the last result when inputs are unchanged, so repeated calls during TransactionController:stateChange no longer redo the full legacy conversion (including per-asset toChecksumAddress / keccak256).

Cache hits compare state slices by reference (assetsBalance, assetsInfo, assetsPrice, networkConfigurationsByChainId), selectedCurrency by value, and accounts / nativeAssetIdentifiers with shallow equality; any real change still runs computeStateForTransactionPay. The conversion logic is unchanged, only split behind the cache layer.

Exports the new FormatStateForTransactionPayParams type and adds memoization unit tests plus a changelog entry.

^{Reviewed by Cursor Bugbot for commit ed31a9a. Bugbot is set up for automated code reviews on this repo. Configure here.}