fix(utils): prevent panic when pushing to a zero-size ring buffer (#4840)

Co-authored-by: Claude <noreply@anthropic.com>

internal/utils/ring_buffer.go

@@ -37,6 +37,11 @@ func RingBufferFrom[T any](size int, data []T) *RingBuffer[T] {
 func (r *RingBuffer[T]) Push(data T) {
 	r.mutex.Lock()
 	defer r.mutex.Unlock()
+	if r.Size <= 0 {
+		// A zero (or negative) capacity buffer holds nothing. Bail out before
+		// indexing r.data or taking a modulo by r.Size, both of which panic.
+		return
+	}
 	if len(r.data) == r.Size {
 		r.data[r.start] = data
 		r.start = (r.start + 1) % r.Size

internal/utils/ring_buffer_test.go

@@ -44,6 +44,24 @@ func TestRingBuffer_MarshalJSON(t *testing.T) {
 	}
 }
 
+func TestRingBuffer_ZeroSize(t *testing.T) {
+	// A zero-capacity buffer must hold nothing rather than panic. This is
+	// reachable from the logs endpoint (?min=0), which builds NewRingBuffer(0).
+	rb := NewRingBuffer[int](0)
+
+	rb.Push(1)
+	rb.Push(2)
+
+	if rb.Len() != 0 {
+		t.Errorf("Expected len to be 0, got %d", rb.Len())
+	}
+
+	data := rb.Data()
+	if len(data) != 0 {
+		t.Errorf("Expected data to be empty, got %v", data)
+	}
+}
+
 func TestRingBuffer_Clear(t *testing.T) {
 	rb := NewRingBuffer[int](3)