P6X4's concurrent page was technically fast and visually fragmented because every backend boundary became its own loading state.
#performance
React 18 made progressive server rendering practical, but useful streaming depended on boundaries shaped around comprehension.
React 18 gave P6X4 new scheduling and streaming capabilities; the interface still needed to speak in product states rather than renderer states.
The original LCP, FID, and CLS set made user-centered performance easier to discuss in 2020, provided I kept field distributions, metric limits, and actual product behavior visible.
A bounded W93H experiment found a real compute win inside one kernel and no justification to move parsing, state, or interface ownership out of JavaScript.
Server-rendering React improved the first response while revealing the bundle, hydration, and ownership costs hidden by shared code.
Multiplexing changed M31V’s request economics in 2015, but a large photograph still cost transfer, decoding, memory, and attention.
A slow phone and an expensive connection turned page weight from a technical afterthought into a product constraint.
T04P behaved well for ten minutes and badly by the sixth hour, exposing timer drift, leaked listeners, unbounded history, and assumptions about browser attention.
CSS made product photographs fit a phone while the network still delivered the desktop originals, forcing image cost into the design itself.