refactor(fast-inbox): source checkpoint consumed messages by leaf-count range (A-1384)

The prover node resolved the boundary Inbox buckets for a checkpoint's leaf-count
range itself before asking for the messages between them. The message source now
takes the leaf counts directly and reports an unresolvable boundary, so drop the
two-step lookup.

Author: spalladino

yarn-project/prover-node/src/prover-node.ts

@@ -14,7 +14,6 @@ import { ChonkCache } from '@aztec/prover-client/orchestrator';
 import { type AvmSimulator, PublicProcessorFactory } from '@aztec/simulator/server';
 import {
   EventDrivenL2BlockStream,
-  type L2Block,
   type L2BlockId,
   type L2BlockSource,
   type L2BlockStreamEvent,
@@ -38,7 +37,6 @@ import {
 import type { DataStoreConfig } from '@aztec/stdlib/kv-store';
 import type { L1ToL2MessageSource } from '@aztec/stdlib/messaging';
 import { MerkleTreeId } from '@aztec/stdlib/trees';
-import type { BlockHeader } from '@aztec/stdlib/tx';
 import {
   L1Metrics,
   type TelemetryClient,
@@ -353,9 +351,13 @@ export class ProverNode implements L2BlockStreamEventHandler, ProverNodeApi, Tra
     const previousBlockNumber = BlockNumber(checkpoint.blocks[0].number - 1);
     const previousBlockHeader = await this.gatherPreviousBlockHeader(previousBlockNumber);
     const lastBlock = checkpoint.blocks.at(-1)!;
-    // Streaming Inbox (AZIP-22 Fast Inbox): the checkpoint's consumed messages are those in the Inbox buckets between
-    // the parent checkpoint's consumed position and this checkpoint's last block (compact leaf-count range).
-    const l1ToL2Messages = await this.deriveCheckpointConsumedMessages(previousBlockHeader, lastBlock);
+    // Streaming Inbox (AZIP-22 Fast Inbox): the checkpoint's consumed messages are those between the parent
+    // checkpoint's consumed position and this checkpoint's last block, as a compact leaf-count range. The prover
+    // slices them per block.
+    const l1ToL2Messages = await this.l1ToL2MessageSource.getL1ToL2MessagesBetweenLeafCounts(
+      BigInt(previousBlockHeader.state.l1ToL2MessageTree.nextAvailableLeafIndex),
+      BigInt(lastBlock.header.state.l1ToL2MessageTree.nextAvailableLeafIndex),
+    );
     const previousInboxRollingHash = await this.gatherPreviousInboxRollingHash(checkpoint.number);
     const lastBlockHash = await lastBlock.header.hash();
     await this.worldState.syncImmediate(lastBlock.number, lastBlockHash);
@@ -372,27 +374,6 @@ export class ProverNode implements L2BlockStreamEventHandler, ProverNodeApi, Tra
     };
   }
 
-  /**
-   * Derives a checkpoint's consumed L1-to-L2 messages, in order, from the Inbox buckets between the parent
-   * checkpoint's consumed position (the block before the checkpoint's first block) and the checkpoint's last block
-   * (compact leaf counts), for the prover to slice per block (AZIP-22 Fast Inbox).
-   */
-  private async deriveCheckpointConsumedMessages(previousBlockHeader: BlockHeader, lastBlock: L2Block): Promise<Fr[]> {
-    const startLeafCount = BigInt(previousBlockHeader.state.l1ToL2MessageTree.nextAvailableLeafIndex);
-    const endLeafCount = BigInt(lastBlock.header.state.l1ToL2MessageTree.nextAvailableLeafIndex);
-    if (endLeafCount <= startLeafCount) {
-      return [];
-    }
-    const startBucket = await this.l1ToL2MessageSource.getInboxBucketByTotalMsgCount(startLeafCount);
-    const endBucket = await this.l1ToL2MessageSource.getInboxBucketByTotalMsgCount(endLeafCount);
-    if (startBucket === undefined || endBucket === undefined) {
-      throw new Error(
-        `Cannot resolve consumed messages for checkpoint ending at block ${lastBlock.number} from the Inbox buckets`,
-      );
-    }
-    return this.l1ToL2MessageSource.getL1ToL2MessagesBetweenBuckets(startBucket.seq, endBucket.seq);
-  }
-
   /**
    * Sources the inbox rolling hash chain-start for a checkpoint: the previous checkpoint's `inboxRollingHash`, or zero
    * for the genesis checkpoint. The prover threads this into the base parity circuits so the rebuilt checkpoint header