Incremental segment prefetching

<section class="stage"><div class="heading">INCREMENTAL PREFETCH <span class="hint">reuse shared layout</span></div><div class="segments"><div class="tile layout">/shop layout <small>cached</small></div><div class="paths"><div class="tile route">/item/A <small>loaded</small></div><div class="tile route new">/item/B <small>fetch</small></div></div></div><div class="caption">Prefetch only the missing segment</div></section>

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