Waveform viewer cold first load slow? Check whether the initial view is zoom-to-fit (it can bypass ranged cold reads)

A server-side waveform reader had a fast cold path: a window over a short range (here at most 25% of the dump time span) was answered by a ranged read, with the whole-signal walk deferred to the background. But the viewer opened every dump at zoom-to-fit, so the first window covered 100% of the time span. That fell back to walking each signal's full history before the first draw: about 30 s for 3 signals on a 10 GB dump, versus a few seconds expected. The incumbent viewer opened on a short range and looked 4x faster on first values. Before blaming the reader, log the first window request (t0, t1 against the file span) and the reply flags (ranged or whole). Fix it on the viewer side by opening on a range around the marker or the time of interest, or on the reader side by answering a whole-span first window with coarse buckets from a sampled pass.