fix(pxe): always inject protocol nullifier in kernelless simulation

Block #24580's mechanical next-boundary re-graft (99cbb5d) pulled the PXE
kernelless-simulation files from the v5 tip, which predates the always-inject
protocol-nullifier scheme introduced by private#487 (4b4245f circuits,
0d643f4 PXE note nonces, d98ceba kernelless sim). That reverted
ExecutionNoteCache and generateSimulatedProvingResult to the old conditional
scheme, while the Noir kernels (with-kernels path) still always inject the
protocol nullifier. The kernelless gas estimate therefore under-counted the
protocol nullifier's DA gas (e.g. 128 vs 192) and note-hash nonces used the
wrong generator, producing the e2e_kernelless_simulation mismatch and the
related "hinted siloed note hash does not match nullified note hash" failures.

Re-apply next's always-inject scheme in the kernelless path:
- ExecutionNoteCache: the nonce generator and the tx first nullifier are always
  the protocol nullifier, and getAllNullifiers always prepends it (restores
  next's file verbatim; drops the vestigial usedProtocolNullifierForNonces flag
  and finish()).
- generateSimulatedProvingResult: unconditionally unshift the protocol nullifier
  as the first non-revertible nullifier, mirroring the init kernel.
- Drop the now-removed noteCache.finish() calls in the PXE simulator and the two
  TXE callers.

Reproduces private#487 / d98ceba, lost in the v5 forward-port.

Author: AztecBot

yarn-project/pxe/src/contract_function_simulator/contract_function_simulator.ts

@@ -314,7 +314,6 @@ export class ContractFunctionSimulator {
       );
       const simulatorTeardownTimer = new Timer();
 
-      noteCache.finish();
       const firstNullifierHint = noteCache.getNonceGenerator();
 
       const publicCallRequests = collectNested([executionResult], r =>
@@ -657,12 +656,12 @@ export async function generateSimulatedProvingResult(
     siloedNullifiers,
     minRevertibleSideEffectCounter,
   );
+  // The protocol nullifier is the nonce generator and the tx's first nullifier. It is injected by the
+  // init kernel (at counter 1, index 0) rather than emitted by any private call, so it is absent from
+  // the executed nullifiers above. Mirror the kernel here by prepending it as the first non-revertible
+  // nullifier.
   const nonceGenerator = privateExecutionResult.firstNullifier;
-  if (nonRevertibleNullifiers.length === 0) {
-    nonRevertibleNullifiers.push(nonceGenerator);
-  } else if (!nonRevertibleNullifiers[0].equals(nonceGenerator)) {
-    throw new Error('The first non revertible nullifier should be equal to the nonce generator. This is a bug!');
-  }
+  nonRevertibleNullifiers.unshift(nonceGenerator);
 
   if (isPrivateOnlyTx) {
     // We must make the note hashes unique by using the

yarn-project/pxe/src/contract_function_simulator/execution_note_cache.ts

@@ -43,12 +43,6 @@ export class ExecutionNoteCache {
 
   private inRevertiblePhase = false;
 
-  /**
-   * Whether the protocol nullifier was used for nonce generation.
-   * We don't need to use the protocol nullifier if a non-revertible nullifier is emitted.
-   */
-  private usedProtocolNullifierForNonces: boolean | undefined;
-
   constructor(private readonly protocolNullifier: Fr) {}
 
   /**
@@ -64,12 +58,9 @@ export class ExecutionNoteCache {
     this.inRevertiblePhase = true;
     this.minRevertibleSideEffectCounter = minRevertibleSideEffectCounter;
 
-    const nullifiers = this.getEmittedNullifiers();
-    // If there are no nullifiers emitted by private calls so far, we use the protocol nullifier as the nonce generator.
-    // Note: There could still be nullifiers emitted after the counter is set, but those nullifiers are revertible, so
-    // we don't want to use them as the nonce generator.
-    this.usedProtocolNullifierForNonces = nullifiers.length === 0;
-    const nonceGenerator = this.usedProtocolNullifierForNonces ? this.protocolNullifier : new Fr(nullifiers[0]);
+    // The protocol nullifier is always the tx's first nullifier (injected by the kernel init), so it is the
+    // nonce generator for every note hash.
+    const nonceGenerator = this.protocolNullifier;
 
     // The existing pending notes are all non-revertible.
     // They cannot be squashed by nullifiers emitted after minRevertibleSideEffectCounter is set.
@@ -102,14 +93,6 @@ export class ExecutionNoteCache {
     return sideEffectCounter >= this.minRevertibleSideEffectCounter;
   }
 
-  public finish() {
-    // If we never entered the revertible phase, and there are no nullifiers emitted, we need to use the protocol
-    // nullifier as the nonce generator.
-    if (!this.inRevertiblePhase) {
-      this.usedProtocolNullifierForNonces = this.getEmittedNullifiers().length === 0;
-    }
-  }
-
   /**
    * Add a new note to cache.
    * @param note - New note created during execution.
@@ -223,19 +206,15 @@ export class ExecutionNoteCache {
   }
 
   /**
-   * @returns All nullifiers emitted by private calls in this transaction. If the protocol nullifier was used as the
-   * nonce generator, it is injected as the first nullifier.
+   * @returns All nullifiers of the transaction: the protocol nullifier (the kernel-injected first nullifier),
+   * followed by those emitted by private calls.
    */
   getAllNullifiers(): Fr[] {
-    if (this.usedProtocolNullifierForNonces === undefined) {
-      throw new Error('usedProtocolNullifierForNonces is not set yet. Call finish() to complete the transaction.');
-    }
-    const allNullifiers = this.getEmittedNullifiers();
-    return [...(this.usedProtocolNullifierForNonces ? [this.protocolNullifier] : []), ...allNullifiers];
+    return [this.protocolNullifier, ...this.getEmittedNullifiers()];
   }
 
   getNonceGenerator(): Fr {
-    return this.getAllNullifiers()[0];
+    return this.protocolNullifier;
   }
 
   #recordNullifier(contractAddress: AztecAddress, siloedNullifier: bigint) {

yarn-project/txe/src/oracle/txe_oracle_top_level_context.ts

@@ -543,7 +543,6 @@ export class TXEOracleTopLevelContext implements IMiscOracle, ITxeExecutionOracl
         }),
       );
 
-      noteCache.finish();
       const nonceGenerator = noteCache.getNonceGenerator();
       result = new PrivateExecutionResult(executionResult, nonceGenerator, publicFunctionsCalldata);
     } catch (err) {

yarn-project/txe/src/utils/tx_effect_creation.ts

@@ -7,8 +7,6 @@ import { TxEffect, TxHash } from '@aztec/stdlib/tx';
 export async function makeTxEffect(noteCache: ExecutionNoteCache, txBlockNumber: BlockNumber): Promise<TxEffect> {
   const txEffect = TxEffect.empty();
 
-  noteCache.finish();
-
   const nonceGenerator = noteCache.getNonceGenerator();
   txEffect.noteHashes = await Promise.all(
     noteCache