fix: Check slash round lifetime when looking back executable rounds

yarn-project/slasher/src/tally_slasher_client.test.ts

@@ -399,6 +399,33 @@ describe('TallySlasherClient', () => {
         expect(tallySlashingProposer.getRound).toHaveBeenCalledWith(0n);
         expect(tallySlashingProposer.getRound).toHaveBeenCalledWith(1n);
       });
+
+      it('should respect lifetimeInRounds when computing oldestExecutableRound', async () => {
+        // Use a large lookBack to test that lifetimeInRounds constrains it
+        tallySlasherClient.updateConfig({ slashExecuteRoundsLookBack: 20 });
+
+        const currentRound = 15n;
+        const currentSlot = currentRound * BigInt(roundSize);
+        const slashingLifetimeInRounds = BigInt(settings.slashingLifetimeInRounds); // 10
+
+        // The oldest executable round should be currentRound - lifetimeInRounds = 15 - 10 = 5
+        // NOT currentRound - executionDelay - 1 - lookBack = 15 - 2 - 1 - 20 = -8 (clamped to 0)
+        const expectedOldestRound = currentRound - slashingLifetimeInRounds; // 5
+
+        // Mock rounds 5-12 as executable (executableRound = currentRound - executionDelay - 1 = 15 - 2 - 1 = 12)
+        tallySlashingProposer.getRound.mockImplementation((round: bigint) =>
+          Promise.resolve(round >= expectedOldestRound && round <= 12n ? executableRoundData : emptyRoundData),
+        );
+
+        const actions = await tallySlasherClient.getProposerActions(currentSlot);
+
+        // Should execute the oldest round (5), not try to execute rounds before that
+        expect(actions).toHaveLength(1);
+        expectActionExecuteSlash(actions[0], expectedOldestRound);
+
+        // Verify we didn't try to check rounds older than the lifetime allows
+        expect(tallySlashingProposer.getRound).not.toHaveBeenCalledWith(expectedOldestRound - 1n);
+      });
     });
 
     describe('multiple', () => {

yarn-project/slasher/src/tally_slasher_client.ts

@@ -187,7 +187,14 @@ export class TallySlasherClient implements ProposerSlashActionProvider, SlasherC
     const slashingExecutionDelayInRounds = BigInt(this.settings.slashingExecutionDelayInRounds);
     const executableRound = currentRound - slashingExecutionDelayInRounds - 1n;
     const lookBack = BigInt(this.config.slashExecuteRoundsLookBack);
-    const oldestExecutableRound = maxBigint(0n, executableRound - lookBack);
+    const slashingLifetimeInRounds = BigInt(this.settings.slashingLifetimeInRounds);
+
+    // Compute the oldest executable round considering both lookBack and lifetimeInRounds
+    // A round is only executable if currentRound <= round + lifetimeInRounds
+    // So the oldest round we can execute is: currentRound - lifetimeInRounds
+    const oldestByLifetime = maxBigint(0n, currentRound - slashingLifetimeInRounds);
+    const oldestByLookBack = maxBigint(0n, executableRound - lookBack);
+    const oldestExecutableRound = maxBigint(oldestByLifetime, oldestByLookBack);
 
     // Check if slashing is enabled at all
     if (!(await this.slasher.isSlashingEnabled())) {
@@ -199,10 +206,12 @@ export class TallySlasherClient implements ProposerSlashActionProvider, SlasherC
       slotNumber,
       currentRound,
       oldestExecutableRound,
+      oldestByLifetime,
+      oldestByLookBack,
       executableRound,
       slashingExecutionDelayInRounds,
       lookBack,
-      slashingLifetimeInRounds: this.settings.slashingLifetimeInRounds,
+      slashingLifetimeInRounds,
     });
 
     // Iterate over all rounds, starting from the oldest, until we find one that is executable
@@ -220,6 +229,7 @@ export class TallySlasherClient implements ProposerSlashActionProvider, SlasherC
   /**
    * Checks if a given round is executable and returns an execute-slash action for it if so.
    * Assumes round number has already been checked against lifetime and execution delay.
+   * @param executableRound - The round to check for execution
    */
   private async tryGetRoundExecuteAction(executableRound: bigint): Promise<ProposerSlashAction | undefined> {
     let logData: Record<string, unknown> = { executableRound };