feat(transaction-controller): add approval-time sponsorship/signing hooks

[pedronfigueiredo]

Related pull requests

• Extension: MetaMask/metamask-extension#46060
• Mobile: MetaMask/metamask-mobile#35754

Summary

• add isSponsored and shouldSign hooks to TransactionControllerOptions['hooks'] so clients supply approval-time sponsorship and local-vs-external signing policy at the approval boundary
• keep gas-fee-token preflight in the approval flow so the controller still refreshes token quotes and native-balance fallback before deciding whether to sign
• preserve beforeSign execution even when the approved transaction ends up on the external-sign path
• keep the Core API surface focused on controller hooks rather than a separate approval-preparation helper

Public API

hooks: {
  isSponsored?: (request: { transactionMeta: TransactionMeta }) => Promise<boolean>;
  shouldSign?: (request: {
    transactionMeta: TransactionMeta;
    isSponsored: boolean;
  }) => Promise<boolean>;
  beforePublish?: (transactionMeta: TransactionMeta) => Promise<boolean>;
  beforeSign?: BeforeSignHook;
  publish?: (transactionMeta: TransactionMeta) => Promise<{ transactionHash: string }>;
  publishBatch?: PublishBatchHook;
}

Behavior decisions

• isSponsored answers whether the transaction should be treated as sponsored at approval time.
• shouldSign answers whether the controller should reserve a nonce and sign locally.
• Sponsorship no longer implies local signing.
• beforeSign still runs before gas-fee-token publication checks, even when the final path does not locally sign.

Validation

• corepack yarn workspace @metamask/transaction-controller run jest --no-watchman --no-coverage packages/transaction-controller/src/TransactionController.test.ts
• corepack yarn build

---

Note

Medium Risk
Changes the core post-approval pipeline (nonce, signing, events) for every transaction, though default hooks mirror prior isGasFeeSponsored / isExternalSign behavior.

Overview
Adds optional isSponsored and shouldSign hooks so clients can decide sponsorship and local vs external signing at approval time, without treating sponsorship as “must sign locally.”

Approval flow is reordered: mark approved → beforeSign → gas-fee-token preflight → run hooks and set isGasFeeSponsored / isExternalSign → only if shouldSign is true, reserve nonce and sign (signing skips duplicate beforeSign / token checks). transactionApproved is emitted after this path so listeners can see a nonce when local signing ran.

Smaller fixes: batch gas poller updates transactionBatches, simulation API creates delegation overrides when missing, getGasFeeTokens returns empty tokens when EIP-7702 key/upgrade address is missing, and removeLeadingZeroes is simplified.

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[pedronfigueiredo]

Fixed the lint:misc:check failure (Prettier formatting in TransactionController.test.ts) and pushed 58ac505. GitHub checks are green again; @matthewwalsh0, could you re-review when you have a moment?