fix: catch potential errors enqueuing gov/slashing signals (#16662)

These promises could throw before the code got to the `await` for them
(where `catch` handlers were attached) leading to an unhandled rejection
and a full process crash.

Author: PhilWindle

yarn-project/sequencer-client/src/sequencer/sequencer.test.ts

@@ -267,6 +267,7 @@ describe('sequencer', () => {
     validatorClient.createBlockProposal.mockImplementation(() => Promise.resolve(createBlockProposal()));
 
     slasherClient = mock<SlasherClientInterface>();
+    slasherClient.getProposerActions.mockResolvedValue([]);
 
     dateProvider = new TestDateProvider();
 

yarn-project/sequencer-client/src/sequencer/sequencer.ts

@@ -412,18 +412,23 @@ export class Sequencer extends (EventEmitter as new () => TypedEventEmitter<Sequ
 
     const enqueueGovernanceSignalPromise =
       this.governanceProposerPayload && !this.governanceProposerPayload.isZero()
-        ? publisher.enqueueGovernanceCastSignal(
-            this.governanceProposerPayload,
-            slot,
-            timestamp,
-            attestorAddress,
-            signerFn,
-          )
-        : Promise.resolve();
+        ? publisher
+            .enqueueGovernanceCastSignal(this.governanceProposerPayload, slot, timestamp, attestorAddress, signerFn)
+            .catch(err => {
+              this.log.error(`Error enqueuing governance vote`, err, { blockNumber: newBlockNumber, slot });
+              return false;
+            })
+        : Promise.resolve(false);
 
     const enqueueSlashingActionsPromise = this.slasherClient
-      ?.getProposerActions(slot)
-      ?.then(actions => publisher.enqueueSlashingActions(actions, slot, timestamp, attestorAddress, signerFn));
+      ? this.slasherClient
+          .getProposerActions(slot)
+          .then(actions => publisher.enqueueSlashingActions(actions, slot, timestamp, attestorAddress, signerFn))
+          .catch(err => {
+            this.log.error(`Error enqueuing slashing actions`, err, { blockNumber: newBlockNumber, slot });
+            return false;
+          })
+      : Promise.resolve(false);
 
     if (invalidateBlock && !this.config.skipInvalidateBlockAsProposer) {
       publisher.enqueueInvalidateBlock(invalidateBlock);
@@ -482,12 +487,7 @@ export class Sequencer extends (EventEmitter as new () => TypedEventEmitter<Sequ
       this.emit('tx-count-check-failed', { minTxs: this.minTxsPerBlock, availableTxs: pendingTxCount });
     }
 
-    await enqueueGovernanceSignalPromise?.catch(err => {
-      this.log.error(`Error enqueuing governance vote`, err, { blockNumber: newBlockNumber, slot });
-    });
-    await enqueueSlashingActionsPromise?.catch(err => {
-      this.log.error(`Error enqueuing slashing actions`, err, { blockNumber: newBlockNumber, slot });
-    });
+    await Promise.all([enqueueGovernanceSignalPromise, enqueueSlashingActionsPromise]);
 
     const l1Response = await publisher.sendRequests();
     const proposedBlock = l1Response?.successfulActions.find(a => a === 'propose');