feat: feature flag to disable relay gas station (#7255)

## Explanation

Add new feature flag property to disable gas station on specific source
chains in Relay.

## References

Related to [#23350
](MetaMask/metamask-mobile#23350)

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs)
- [x] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Introduces `relayDisabledGasStationChains` feature flag and uses it to
skip gas station logic on specified source chains; updates feature flag
utils and tests.
> 
> - **Relay strategy (`src/strategy/relay/relay-quotes.ts`)**
> - Read `relayDisabledGasStationChains` from feature flags and bypass
gas fee token path when the source chain is listed.
> - **Feature flags utils (`src/utils/feature-flags.ts`)**
> - Add `relayDisabledGasStationChains` to raw and normalized types with
default `[]`.
> - **Tests**
> - Add coverage for disabled-chain behavior in `relay-quotes.test.ts`.
> - Extend `feature-flags.test.ts` to assert new flag defaults and
remote values.
> - **Changelog**
>   - Document new flag usage under Unreleased.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
40dd5c5. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: matthewwalsh0

packages/transaction-pay-controller/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Use `relayDisabledGasStationChains` feature flag to disable gas station on specific source chains in Relay strategy ([#7255](https://github.com/MetaMask/core/pull/7255))
+
 ### Changed
 
 - Bump `@metamask/bridge-status-controller` from `^63.0.0` to `^63.1.0` ([#7245](https://github.com/MetaMask/core/pull/7245))

packages/transaction-pay-controller/src/strategy/relay/relay-quotes.test.ts

@@ -645,6 +645,46 @@ describe('Relay Quotes Utils', () => {
           }),
         );
       });
+
+      it('not using gas fee token cost if chain disabled in feature flag', async () => {
+        successfulFetchMock.mockResolvedValue({
+          json: async () => QUOTE_MOCK,
+        } as never);
+
+        getTokenBalanceMock.mockReturnValue('1724999999999999');
+        getGasFeeTokensMock.mockResolvedValue([GAS_FEE_TOKEN_MOCK]);
+
+        getRemoteFeatureFlagControllerStateMock.mockReturnValue({
+          cacheTimestamp: 0,
+          remoteFeatureFlags: {
+            confirmations_pay: {
+              relayDisabledGasStationChains: [QUOTE_REQUEST_MOCK.sourceChainId],
+            },
+          },
+        });
+
+        const result = await getRelayQuotes({
+          messenger,
+          requests: [QUOTE_REQUEST_MOCK],
+          transaction: TRANSACTION_META_MOCK,
+        });
+
+        expect(result[0].fees.isSourceGasFeeToken).toBeUndefined();
+        expect(result[0].fees.sourceNetwork).toStrictEqual({
+          estimate: {
+            fiat: '4.56',
+            human: '1.725',
+            raw: '1725000000000000',
+            usd: '3.45',
+          },
+          max: {
+            fiat: '4.56',
+            human: '1.725',
+            raw: '1725000000000000',
+            usd: '3.45',
+          },
+        });
+      });
     });
 
     it('includes target network fee in quote', async () => {

packages/transaction-pay-controller/src/strategy/relay/relay-quotes.ts

@@ -372,6 +372,7 @@ async function calculateSourceNetworkCost(
 > {
   const { from, sourceChainId, sourceTokenAddress } = request;
   const allParams = quote.steps.flatMap((s) => s.items).map((i) => i.data);
+  const { relayDisabledGasStationChains } = getFeatureFlags(messenger);
 
   const { chainId, data, maxFeePerGas, maxPriorityFeePerGas, to, value } =
     allParams[0];
@@ -420,6 +421,15 @@ async function calculateSourceNetworkCost(
     return { estimate, max };
   }
 
+  if (relayDisabledGasStationChains.includes(sourceChainId)) {
+    log('Skipping gas station as disabled chain', {
+      sourceChainId,
+      disabledChainIds: relayDisabledGasStationChains,
+    });
+
+    return { estimate, max };
+  }
+
   log('Checking gas fee tokens as insufficient native balance', {
     nativeBalance,
     max: max.raw,

packages/transaction-pay-controller/src/utils/feature-flags.test.ts

@@ -9,6 +9,7 @@ import { getMessengerMock } from '../tests/messenger-mock';
 const GAS_FALLBACK_ESTIMATE_MOCK = 123;
 const GAS_FALLBACK_MAX_MOCK = 456;
 const RELAY_QUOTE_URL_MOCK = 'https://test.com/test';
+const RELAY_GAS_STATION_DISABLED_CHAINS_MOCK = ['0x1', '0x2'];
 
 describe('Feature Flags Utils', () => {
   const { messenger, getRemoteFeatureFlagControllerStateMock } =
@@ -28,6 +29,7 @@ describe('Feature Flags Utils', () => {
       const featureFlags = getFeatureFlags(messenger);
 
       expect(featureFlags).toStrictEqual({
+        relayDisabledGasStationChains: [],
         relayFallbackGas: {
           estimate: DEFAULT_RELAY_FALLBACK_GAS_ESTIMATE,
           max: DEFAULT_RELAY_FALLBACK_GAS_MAX,
@@ -41,6 +43,8 @@ describe('Feature Flags Utils', () => {
         cacheTimestamp: 0,
         remoteFeatureFlags: {
           confirmations_pay: {
+            relayDisabledGasStationChains:
+              RELAY_GAS_STATION_DISABLED_CHAINS_MOCK,
             relayFallbackGas: {
               estimate: GAS_FALLBACK_ESTIMATE_MOCK,
               max: GAS_FALLBACK_MAX_MOCK,
@@ -53,6 +57,7 @@ describe('Feature Flags Utils', () => {
       const featureFlags = getFeatureFlags(messenger);
 
       expect(featureFlags).toStrictEqual({
+        relayDisabledGasStationChains: RELAY_GAS_STATION_DISABLED_CHAINS_MOCK,
         relayFallbackGas: {
           estimate: GAS_FALLBACK_ESTIMATE_MOCK,
           max: GAS_FALLBACK_MAX_MOCK,

packages/transaction-pay-controller/src/utils/feature-flags.ts

@@ -1,3 +1,4 @@
+import type { Hex } from '@metamask/utils';
 import { createModuleLogger } from '@metamask/utils';
 
 import type { TransactionPayControllerMessenger } from '..';
@@ -11,6 +12,7 @@ export const DEFAULT_RELAY_FALLBACK_GAS_MAX = 1500000;
 export const DEFAULT_RELAY_QUOTE_URL = `${RELAY_URL_BASE}/quote`;
 
 type FeatureFlagsRaw = {
+  relayDisabledGasStationChains?: Hex[];
   relayFallbackGas?: {
     estimate?: number;
     max?: number;
@@ -19,6 +21,7 @@ type FeatureFlagsRaw = {
 };
 
 export type FeatureFlags = {
+  relayDisabledGasStationChains: Hex[];
   relayFallbackGas: {
     estimate: number;
     max: number;
@@ -49,7 +52,11 @@ export function getFeatureFlags(
 
   const relayQuoteUrl = featureFlags.relayQuoteUrl ?? DEFAULT_RELAY_QUOTE_URL;
 
+  const relayDisabledGasStationChains =
+    featureFlags.relayDisabledGasStationChains ?? [];
+
   const result = {
+    relayDisabledGasStationChains,
     relayFallbackGas: {
       estimate,
       max,