fix: incorrect initialization

src/zkbob/utils/ZkBobAccounting.sol

@@ -140,13 +140,12 @@ contract ZkBobAccounting is IZkBobAccounting, Ownable {
         slot0 = Slot0({
             maxWeeklyAvgTvl: _maxWeeklyAvgTvl,
             maxWeeklyTxCount: _maxWeeklyTxCount,
-            tailSlot: 0,
+            tailSlot: curSlot,
             headSlot: curSlot,
             cumTvl: _cumTvl,
             txCount: _txCount
         });
         slot1 = Slot1({tvl: _tvl});
-        snapshots[0] = Snapshot({nextSlot: curSlot, txCount: _txCount, cumTvl: _cumTvl});
     }
 
     /**
@@ -309,7 +308,7 @@ contract ZkBobAccounting is IZkBobAccounting, Ownable {
         // however, in order to keep constant gas usage, "if" is being used
         // this can lead to a longer sliding window (> 1 week) in some cases,
         // but eventually it will converge back to the 1 week target
-        if (s0.txCount > 0 && curSlot - s0.tailSlot > WEEK_SLOTS) {
+        if (s0.headSlot > s0.tailSlot && curSlot - s0.tailSlot > WEEK_SLOTS) {
             // if tail is more than 1 week behind, we move tail pointer to the next snapshot
             Snapshot memory sn = snapshots[s0.tailSlot];
             delete snapshots[s0.tailSlot];

test/zkbob/utils/ZkBobAccounting.t.sol

@@ -113,6 +113,20 @@ contract ZkBobAccountingTest is Test {
         _checkStats({_maxWeeklyAvgTvl: 200, _maxWeeklyTxCount: 504, _txCount: 1207});
     }
 
+    function testNoWeeklyActivity() public {
+        pool.recordOperation(IZkBobAccounting.TxType.Common, user1, int256(100 gwei));
+        pool.recordOperation(IZkBobAccounting.TxType.Common, user1, 0);
+
+        vm.warp(block.timestamp + 10 days);
+
+        for (uint256 i = 0; i < 10; i++) {
+            pool.recordOperation(IZkBobAccounting.TxType.Common, user1, 0);
+            vm.warp(block.timestamp + 1 days);
+        }
+
+        _checkStats({_maxWeeklyAvgTvl: 100, _maxWeeklyTxCount: 7, _txCount: 12});
+    }
+
     function testDepositCap() public {
         pool.setLimits(0, 1000 gwei, 500 gwei, 500 gwei, 300 gwei, 100 gwei, 0, 0);