docs: the acquire() guard says what it actually guards, now that the drain sits outside it

src/channel.cpp

@@ -31,6 +31,8 @@ ChannelBuffer::ChannelBuffer(std::shared_ptr<const plot::data::RingBuffer<f32>>
 
 void ChannelBuffer::acquire() noexcept {
   const u64 produced = values_->produced();
+  // Nothing new skips the append pass only: the backfill drain at the end of this function
+  // runs either way, because a late packet can land in a frame interval that pushed nothing.
   if (produced > published_) {
     // A producer that lapped this ring -- a long trigger wait, or a store that was
     // not being published for a while -- makes the incremental append meaningless:
@@ -38,7 +40,6 @@ void ChannelBuffer::acquire() noexcept {
     // Rebuilding from the retained window is O(capacity) once, and it is the only
     // way the published window stays coherent (an empty or garbled window is what
     // "the trace disappeared" looks like from outside).
-    // Nothing new; still allow the window to slide if another reader dropped it.
     if (produced - published_ > values_->capacity()) {
       published_ = 0;
       pyramid_.clear();