feat(perps-controller): report the winning fee source on fee quotes

packages/perps-controller/CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Add optional `PerpsAccountSigner.getChainId`. When set, HyperLiquid user-signed actions (builder fee approval, withdrawals, transfers) are signed for the chain it returns instead of chain 1, so a wallet that only signs for its connected chain does not switch chains ([#10643](https://github.com/MetaMask/core/pull/10643))
+- Add optional `feeSource` to `FeeCalculationResult`, reporting which fee source (`default`, `rewards` or `subscription`) won the fee resolution the quoted MetaMask fee was priced from, so clients can attribute the discount shown in a fee preview without re-deriving it from the rates ([#10650](https://github.com/MetaMask/core/pull/10650))
+  - Absent when the quote was not re-priced from a fee resolution, for example a placement that carries no MetaMask builder fee
+  - `rewards` can carry a 0% discount, so check `metamaskFeeRate` before presenting it as a reduction
 
 ### Changed
 

packages/perps-controller/src/types/index.ts

@@ -1807,6 +1807,21 @@ export type FeeCalculationResult = {
    */
   chargesMetamaskBuilderFee?: boolean;
 
+  /**
+   * Fee source whose rate the MetaMask fee above was priced from: the winner
+   * of the unified fee resolution this quote was computed with.
+   *
+   * Absent when the quote was not re-priced from a resolution, e.g. a
+   * placement that carries no MetaMask builder fee. `subscription` always
+   * implies a reduced fee. `rewards` can win a tie with the default, so it may
+   * carry a 0% discount; check `metamaskFeeRate` before presenting it as a
+   * reduction.
+   *
+   * Describes this preview only. The submit path resolves the fee again, so
+   * the order is attributed to whichever source wins at submission.
+   */
+  feeSource?: PerpsFeeSource;
+
   // Optional detailed breakdown for transparency
   breakdown?: {
     baseFeeRate: number;

packages/perps-controller/src/utils/subscriptionFeeWaiver.ts

@@ -373,7 +373,8 @@ export function quantizeBuilderFeeTenthsBps(discountBips: number): number {
  * placement carries a MetaMask builder fee at all, or undefined when it does not
  * report one. Distinguishes a genuine zero (a TWAP, for instance) from the zero
  * a concurrent fully-waived submit leaves in provider state.
- * @returns The quote with its MetaMask component and totals re-priced.
+ * @returns The quote with its MetaMask component and totals re-priced, tagged
+ * with the fee source they were priced from.
  */
 export function applyFeeResolution(params: {
   fees: FeeCalculationResult;
@@ -430,6 +431,7 @@ export function applyFeeResolution(params: {
     ...fees,
     metamaskFeeRate,
     feeRate,
+    feeSource: resolution.source,
     ...(notional !== undefined && {
       metamaskFeeAmount: notional * metamaskFeeRate,
       feeAmount: notional * feeRate,

packages/perps-controller/tests/src/utils/subscriptionFeeWaiver.test.ts

@@ -404,6 +404,24 @@ describe('applyFeeResolution', () => {
     expect(priced.feeRate).toBeCloseTo(0.0012, 10);
     expect(priced.metamaskFeeAmount).toBeCloseTo(0.75, 10);
     expect(priced.feeAmount).toBeCloseTo(1.2, 10);
+    expect(priced.feeSource).toBe('subscription');
+  });
+
+  it('reports the rewards source when a rewards discount won', () => {
+    const priced = applyFeeResolution({
+      fees,
+      resolution: {
+        // A 65% rewards discount off the 10-bip default.
+        feeBips: 3.5,
+        discountBips: 6500,
+        source: 'rewards',
+        subscription: createStatus({ eligible: false, reason: 'no-source' }),
+      },
+      amount: '1000',
+    });
+
+    expect(priced.metamaskFeeRate).toBeCloseTo(0.00035, 10);
+    expect(priced.feeSource).toBe('rewards');
   });
 
   it('zeroes the MetaMask component on a full waiver', () => {
@@ -467,6 +485,7 @@ describe('applyFeeResolution', () => {
     // The full 10-bip builder fee, not the 5-bip rate the provider carried.
     expect(priced.metamaskFeeRate).toBeCloseTo(0.001, 10);
     expect(priced.feeRate).toBeCloseTo(0.00145, 10);
+    expect(priced.feeSource).toBe('default');
   });
 
   it.each(['-1000', '0'])(
@@ -574,6 +593,7 @@ describe('applyFeeResolution', () => {
     });
 
     expect(priced.metamaskFeeRate).toBe(0);
+    expect(priced.feeSource).toBe('subscription');
     // The previously quoted amounts are left as the provider reported them.
     expect(priced.metamaskFeeAmount).toBe(fees.metamaskFeeAmount);
   });