test(e2e_fees): bridge fee juice from a dedicated L1 account (#24054)

## What

`e2e_fees/account_init` → *"account pays its own fee › pays natively in
the Fee Juice by bridging funds themselves"* flakes while preparing L1
fee juice (before the account deploy), failing on the bridge write:

```
ContractFunctionExecutionError: ... contract function "depositToAztecPublic"
  from:    0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266
  Details: replacement transaction underpriced
```

CI: http://ci.aztec-labs.com/60b00f39a7a0e3cc

## Why

The fee-juice bridge test harness does direct L1 writes (`mint` →
`approve` → `depositToAztecPublic`) through a plain viem client with
**no nonce manager**, so each write picks its nonce via
`getTransactionCount('pending')`. That client uses Anvil account
`0xf39f…92266` (mnemonic index 0) — which is **also the sequencer
publisher account**. The publisher tracks its own nonce in
`l1-tx-utils`, independently of the test client.

When a test write and a publisher checkpoint tx land on the same nonce
concurrently, the higher-priced publisher tx wins and the test's
lower-priced tx is rejected. In the failed run the publisher was sending
on account #0 at ~95–120 gwei:

```
node:l1-tx-utils Sent L1 transaction 0x9652… {nonce: 67, account: 0xf39f…92266, maxFeePerGas: "95.396…"}
```

while the test's `depositToAztecPublic` went out on the same account at
nonce **60** / ~26 gwei → `replacement transaction underpriced`.

The shared-account race is pre-existing but rarely hit; #24037 (changing
publisher send timing) makes the overlap more likely, which surfaced it.

## Fix

Send the harness's direct L1 writes from a dedicated mnemonic account
(`L1_DIRECT_WRITE_ACCOUNT_INDEX = 1`) instead of the deployer/publisher
account #0. Index 1 is unused by any L1-tx sender in these setups
(publisher = 0, prover = 2, validators = 3+), so the test's writes no
longer share a nonce stream with the publisher. Affects `FeesTest` and
`ClientFlowsBenchmark`.

Author: spalladino

yarn-project/end-to-end/src/bench/client_flows/client_flows_benchmark.ts

@@ -28,7 +28,12 @@ import type { ContractInstanceWithAddress } from '@aztec/stdlib/contract';
 import { Gas, GasSettings } from '@aztec/stdlib/gas';
 import { deriveSigningKey } from '@aztec/stdlib/keys';
 
-import { AUTOMINE_E2E_OPTS, MNEMONIC, getPaddedMaxFeesPerGas } from '../../fixtures/fixtures.js';
+import {
+  AUTOMINE_E2E_OPTS,
+  L1_DIRECT_WRITE_ACCOUNT_INDEX,
+  MNEMONIC,
+  getPaddedMaxFeesPerGas,
+} from '../../fixtures/fixtures.js';
 import { type EndToEndContext, type SetupOptions, deployAccounts, setup, teardown } from '../../fixtures/setup.js';
 import { mintTokensToPrivate } from '../../fixtures/token_utils.js';
 import { setupSponsoredFPC } from '../../fixtures/utils.js';
@@ -244,7 +249,15 @@ export class ClientFlowsBenchmark {
     this.feeJuiceBridgeTestHarness = await FeeJuicePortalTestingHarnessFactory.create({
       aztecNode: this.context.aztecNodeService,
       aztecNodeAdmin: this.context.aztecNodeService,
-      l1Client: this.context.deployL1ContractsValues.l1Client,
+      // Bridge from a dedicated L1 account so its direct writes don't race the sequencer publisher's
+      // txs on the deployer account (see L1_DIRECT_WRITE_ACCOUNT_INDEX).
+      l1Client: createExtendedL1Client(
+        this.context.config.l1RpcUrls,
+        MNEMONIC,
+        undefined,
+        undefined,
+        L1_DIRECT_WRITE_ACCOUNT_INDEX,
+      ),
       wallet: this.adminWallet,
       logger: this.logger,
     });

yarn-project/end-to-end/src/e2e_fees/fees_test.ts

@@ -23,7 +23,7 @@ import type { AztecNodeAdmin } from '@aztec/stdlib/interfaces/client';
 
 import { getContract } from 'viem';
 
-import { MNEMONIC, getPaddedMaxFeesPerGas } from '../fixtures/fixtures.js';
+import { L1_DIRECT_WRITE_ACCOUNT_INDEX, MNEMONIC, getPaddedMaxFeesPerGas } from '../fixtures/fixtures.js';
 import {
   type EndToEndContext,
   type SetupOptions,
@@ -230,7 +230,15 @@ export class FeesTest {
     this.feeJuiceBridgeTestHarness = await FeeJuicePortalTestingHarnessFactory.create({
       aztecNode: this.context.aztecNodeService,
       aztecNodeAdmin: this.context.aztecNodeService,
-      l1Client: this.context.deployL1ContractsValues.l1Client,
+      // Bridge from a dedicated L1 account so its direct writes don't race the sequencer publisher's
+      // txs on the deployer account (see L1_DIRECT_WRITE_ACCOUNT_INDEX).
+      l1Client: createExtendedL1Client(
+        this.context.config.l1RpcUrls,
+        MNEMONIC,
+        undefined,
+        undefined,
+        L1_DIRECT_WRITE_ACCOUNT_INDEX,
+      ),
       wallet: this.wallet,
       logger: this.logger,
     });

yarn-project/end-to-end/src/fixtures/fixtures.ts

@@ -109,6 +109,14 @@ export const TEST_PEER_CHECK_INTERVAL_MS = 1000;
 export const TEST_MAX_PENDING_TX_POOL_COUNT = 10_000; // Number of max pending TXs ~ 1.56GB
 
 export const MNEMONIC = 'test test test test test test test test test test test junk';
+
+// Mnemonic account index for tests that issue direct L1 writes (e.g. bridging fee juice) while a
+// sequencer is running. The deployer/sequencer publisher uses index 0, the prover index 2, and
+// validators index 3+. Test-side viem writes and the publisher's l1-tx-utils track nonces
+// independently, so sharing an account causes "replacement transaction underpriced" races; index 1
+// is otherwise unused, so issuing those writes from it keeps them off the publisher's nonce stream.
+export const L1_DIRECT_WRITE_ACCOUNT_INDEX = 1;
+
 export const privateKey = Buffer.from('ac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80', 'hex');
 export const privateKey2 = Buffer.from('59c6995e998f97a5a0044966f0945389dc9e86dae88c7a8412f4603b6b78690d', 'hex');