fix(lint): address gosec G115 integer overflow warnings

Add nolint directives for safe integer conversions where values are
bounded by design (config limits, beacon chain constraints, blob indices).
Add validation for negative slot values in NewSlotFromString.

Author: samcm

pkg/beacon/default.go

@@ -750,6 +750,7 @@ func (d *Default) ListFinalizedSlots(ctx context.Context) ([]phase0.Slot, error)
 
 	latestSlot := phase0.Slot(uint64(finality.Finalized.Epoch) * uint64(sp.SlotsPerEpoch))
 
+	//nolint:gosec // G115: HistoricalEpochCount is a small positive config value, safe to convert
 	for i, val := uint64(latestSlot), uint64(latestSlot)-uint64(sp.SlotsPerEpoch)*uint64(d.config.HistoricalEpochCount); i > val; i -= uint64(sp.SlotsPerEpoch) {
 		slots = append(slots, phase0.Slot(i))
 	}

pkg/beacon/download.go

@@ -173,10 +173,12 @@ func (d *Default) fetchHistoricalCheckpoints(ctx context.Context, checkpoint *v1
 	// We'll derive the current finalized slot and then work back in intervals of SLOTS_PER_EPOCH.
 	currentSlot := uint64(checkpoint.Finalized.Epoch) * uint64(sp.SlotsPerEpoch)
 	for i := 1; i < d.config.HistoricalEpochCount; i++ {
+		//nolint:gosec // G115: i is a positive loop counter bounded by HistoricalEpochCount
 		if uint64(i)*uint64(sp.SlotsPerEpoch) > currentSlot {
 			break
 		}
 
+		//nolint:gosec // G115: i is a positive loop counter bounded by HistoricalEpochCount
 		slot := phase0.Slot(currentSlot - uint64(i)*uint64(sp.SlotsPerEpoch))
 
 		slotsInScope[slot] = struct{}{}

pkg/beacon/expire_test.go

@@ -13,10 +13,12 @@ var (
 )
 
 func CalculateSlotExpiration(slot phase0.Slot, slotsOfHistory int) phase0.Slot {
+	//nolint:gosec // G115: slotsOfHistory is a small positive test value
 	return slot + phase0.Slot(slotsOfHistory)
 }
 
 func GetSlotTime(slot phase0.Slot, secondsPerSlot time.Duration, genesis time.Time) time.Time {
+	//nolint:gosec // G115: slot values are bounded by beacon chain limits, safe for duration
 	return genesis.Add(time.Duration(slot) * secondsPerSlot)
 }
 

pkg/eth/slot.go

@@ -14,6 +14,7 @@ type SlotTime struct {
 }
 
 func CalculateSlotTime(slot phase0.Slot, genesisTime time.Time, durationPerSlot time.Duration) SlotTime {
+	//nolint:gosec // G115: slot values are bounded by beacon chain limits, safe for duration
 	slotStartTime := genesisTime.Add(time.Duration(slot) * durationPerSlot).UTC()
 
 	return SlotTime{

pkg/service/eth/block_id.go

@@ -88,6 +88,10 @@ func NewSlotFromString(id string) (phase0.Slot, error) {
 		return 0, err
 	}
 
+	if slot < 0 {
+		return 0, errors.New("slot cannot be negative")
+	}
+
 	return phase0.Slot(slot), nil
 }
 

pkg/service/eth/eth.go

@@ -572,6 +572,7 @@ func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier, ind
 
 		// Find the sidecar with the given index
 		for i, sidecar := range sidecars {
+			//nolint:gosec // G115: blob indices are small values (max 6), safe to convert
 			if index == int(sidecar.Index) {
 				filtered = append(filtered, sidecars[i])