Experimental cached navigations

<section class="stage"><div class="heading">CACHED NAVIGATION <span class="hint">first visit / revisit</span></div><div class="nav"><div class="tile page-a">PAGE A</div><div class="track"><i></i></div><div class="tile page-b">PAGE B</div></div><div class="status" id="nav-status">A → B: network</div><div class="caption">On return, stored RSC data replaces a fetch</div></section>

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