Merge nucleic/calm-willow-ibis-dozm into main

Mirrored from corpo dad941a.

src/pages/index.astro

@@ -141,6 +141,19 @@ const canonical = new URL('/', Astro.site);
                     </a>
                   </div>
 
+                  <!-- The scrollbar is hidden by design, so nothing on the page says
+                       there is more of it. This does: a segment per product, the
+                       current one filling as its beat is scrolled through. The
+                       segments are built by the enhancement from the cards
+                       themselves, so a product added to the stack cannot leave a
+                       stale one behind. -->
+                  <div class="technology-progress">
+                    <div class="technology-track" data-technology-track aria-hidden="true"></div>
+
+                    <p class="technology-hint" data-technology-hint>
+                      Scroll <span class="technology-hint-arrow" aria-hidden="true">↓</span>
+                    </p>
+
                     <div class="technology-index" role="status" aria-live="polite" aria-atomic="true">
                       <span class="technology-index-current" data-technology-progress-current>01</span>
                       <span aria-hidden="true">/</span>
@@ -148,6 +161,7 @@ const canonical = new URL('/', Astro.site);
                     </div>
                   </div>
                 </div>
+              </div>
 
               <div class="technology-steps" aria-hidden="true">
                 <span data-technology-step="0"></span>
@@ -457,6 +471,7 @@ const canonical = new URL('/', Astro.site);
 
   .card-index,
   .technology-index,
+  .technology-hint,
   .footer {
     font-family: 'JetBrains Mono', monospace;
     font-size: 0.78rem;
@@ -527,10 +542,13 @@ const canonical = new URL('/', Astro.site);
 
   /* Scroll length is per story beat, not a fixed page height: a card added to the
      stack has to lengthen this or every beat gets shorter. Sized so three beats each
-     hold the stage for about as long as the two-card stack gave one. */
+     hold the stage for about as long as the two-card stack gave one. The upper bound
+     is what a tall window actually runs into — at 1400px tall the old one left the
+     whole story about 490px of scroll, a third of it for the last product. It has to
+     clear the tallest viewport by enough to still be a scroll. */
   .hero-lead.has-scroll-stack {
     position: relative;
-    min-height: clamp(66rem, 178svh, 103rem);
+    min-height: clamp(66rem, 178svh, 140rem);
     align-items: stretch;
   }
 
@@ -810,12 +828,90 @@ const canonical = new URL('/', Astro.site);
     line-height: 1.45;
   }
 
+  /* Only the scrolling story has progress to report; the static list below the
+     enhancement's own conditions has none, and says nothing. */
+  .technology-progress {
+    display: none;
+    grid-template-columns: 1fr auto;
+    align-items: center;
+    margin-top: 1.05rem;
+    row-gap: 0.6rem;
+    column-gap: 1rem;
+  }
+
+  .is-scroll-stack .technology-progress {
+    display: grid;
+  }
+
+  .technology-track {
+    display: grid;
+    grid-column: 1 / -1;
+    grid-auto-flow: column;
+    /* Equal shares on purpose, unlike the step boxes they measure: these say which
+       product of how many, not how much scroll each one happens to cost. */
+    grid-auto-columns: 1fr;
+    gap: 0.4rem;
+  }
+
+  .technology-track span {
+    position: relative;
+    height: 2px;
+    /* Same hairline as every rule on the page, so the empty track reads as part of
+       the composition rather than as a control sitting on top of it. */
+    background: var(--line);
+  }
+
+  /* The fill is a scaled bar, not a width: it is written on every scroll frame, and
+     transform is the one property that costs neither layout nor paint to change. */
+  .technology-track span::after {
+    position: absolute;
+    inset: 0;
+    background: var(--pine);
+    content: '';
+    transform: scaleX(var(--beat-fill, 0));
+    transform-origin: left;
+  }
+
+  .technology-hint {
+    display: flex;
+    align-items: center;
+    gap: 0.4rem;
+    margin: 0;
+    color: var(--muted);
+    transition: opacity 500ms ease;
+  }
+
+  /* Said once. The first scroll is proof it has been read, and it does not come back
+     — an instruction that outlives its own need is the obtrusive kind. */
+  .technology-hint.is-read {
+    opacity: 0;
+  }
+
+  /* A long hold, then a single fall: a continuous bob reads as decoration, where one
+     nudge every few seconds reads as the page pointing somewhere. Scoped to the
+     unread hint so the loop ends with the thing it was pointing at — an invisible
+     element still animating is a frame's work every few seconds forever. */
+  .technology-hint:not(.is-read) .technology-hint-arrow {
+    animation: hint-fall 3.6s 1.4s ease-in-out infinite;
+  }
+
+  @keyframes hint-fall {
+    0%,
+    72%,
+    100% {
+      transform: translateY(0);
+    }
+
+    84% {
+      transform: translateY(0.3em);
+    }
+  }
+
   .technology-index {
     display: none;
     align-items: center;
     justify-content: flex-end;
     gap: 0.45rem;
-    margin-top: 0.75rem;
     color: var(--muted);
   }
 
@@ -838,11 +934,14 @@ const canonical = new URL('/', Astro.site);
      middle of the viewport, and the stack's own top edge starts well below it, so
      the opening box has to be the longest simply to reach that band — split evenly,
      the first product would flick past in a third of the scroll the middle one gets.
-     Measured against the rendered page: these hold each product for within ~10% of
+     The closing box is the other way round: it is the last thing before the page
-     the same distance from 700px to 1100px tall. */
+     runs out, so what it holds is whatever scroll is left after it starts, and
+     giving it a bigger share only takes that away. Measured against the rendered
+     page from 720px to 1400px tall, at ordinary and enlarged text: these hold each
+     product for within ~30% of the same distance, most sizes within ~10%. */
   .is-scroll-stack .technology-steps {
     display: grid;
-    grid-template-rows: 44% 19% 37%;
+    grid-template-rows: 40% 18% 42%;
   }
 
   /* The wrapped fallback pins its card near the top of the viewport rather than at
@@ -1015,11 +1114,11 @@ const canonical = new URL('/', Astro.site);
     }
 
     /* Scroll length for the story, and nothing else — the card no longer spends any
-       of it travelling, so a full viewport of it would read as a dead stretch. Holds
+       of it travelling, so a full viewport of it would read as a dead stretch. Three
-       the phone's pace from the two-card stack across three beats rather than making
+       beats need more of it than two did: at 90svh the last product held the stage
-       the story a third longer again. */
+       for under 60px, which is inside a single flick. */
     .has-scroll-stack .technology-stack {
-      min-height: 90svh;
+      min-height: 110svh;
     }
 
     /* The script pins this at the card's own resting offset. The clamp is the fallback
@@ -1033,12 +1132,13 @@ const canonical = new URL('/', Astro.site);
       min-height: 11.9rem;
     }
 
-    /* The same unequal split as the desktop stack, retuned: a phone's step boxes are
+    /* The same reasoning as the desktop stack, landing somewhere else: a phone's
-       read against the same centre band, but the stack starts much further down its
+       stack begins so far down its own scroll that the opening box has nearly
-       own scroll, so the opening share is larger again. Measured across 640–932px
+       reached the band before the story starts, so here it wants the smallest share
-       tall, these keep the three products within ~25% of one another. */
+       rather than the largest. Measured across 640–932px tall, at ordinary and
+       enlarged text, these keep the three products within ~65% of one another. */
     .is-scroll-stack .technology-steps {
-      grid-template-rows: 29% 19% 52%;
+      grid-template-rows: 13% 25% 62%;
     }
 
     /* One line each: side by side these two need ~360px of tracking-heavy mono, which
@@ -1144,6 +1244,8 @@ const canonical = new URL('/', Astro.site);
     const cards = [...technologyStack.querySelectorAll<HTMLAnchorElement>('[data-technology-card]')];
     const steps = [...technologyStack.querySelectorAll<HTMLElement>('[data-technology-step]')];
     const progressCurrent = technologyStack.querySelector<HTMLElement>('[data-technology-progress-current]');
+    const progressTrack = technologyStack.querySelector<HTMLElement>('[data-technology-track]');
+    const progressHint = technologyStack.querySelector<HTMLElement>('[data-technology-hint]');
     const mobileLayout = window.matchMedia('(max-width: 720px)');
 
     heroLead?.classList.add('has-scroll-stack');
@@ -1241,8 +1343,15 @@ const canonical = new URL('/', Astro.site);
 
     syncEnhancedLayout();
 
+    /* Anything that moves the pins moves the offsets the keyboard and the progress
+       track are measured against, so the two re-read together. Both of these run
+       after this script has finished evaluating, which is the only reason they can
+       name a function declared further down it. */
     if ('ResizeObserver' in window && scrollRoot && heroCopy && technologyStage) {
-      const pinObserver = new ResizeObserver(syncInsets);
+      const pinObserver = new ResizeObserver(() => {
+        syncInsets();
+        measureBeats();
+      });
       pinObserver.observe(scrollRoot);
       pinObserver.observe(heroCopy);
       pinObserver.observe(technologyStage);
@@ -1253,7 +1362,10 @@ const canonical = new URL('/', Astro.site);
       'resize',
       () => {
         cancelAnimationFrame(resizeFrame);
-        resizeFrame = requestAnimationFrame(syncEnhancedLayout);
+        resizeFrame = requestAnimationFrame(() => {
+          syncEnhancedLayout();
+          measureBeats();
+        });
       },
       { passive: true },
     );
@@ -1273,7 +1385,7 @@ const canonical = new URL('/', Astro.site);
     /* A card waits below the active one and leaves above it, so which side of the
        composition a given card sits on depends on where the story currently is — the
        markup class is only the resting state of the stack before any of this runs. */
-    const activateTechnology = (index: number) => {
+    const showTechnology = (index: number) => {
       cards.forEach((card, cardIndex) => {
         const isActive = cardIndex === index;
         card.classList.toggle('is-active', isActive);
@@ -1286,7 +1398,46 @@ const canonical = new URL('/', Astro.site);
       setFooterVisible(index === cards.length - 1);
     };
 
-    activateTechnology(0);
+    /* Each card holds the stage for a few hundred pixels of scroll, so one coarse
+       gesture — a flung trackpad, Page Down — crosses a whole card in a single frame.
+       Its box and the next one's then arrive in the same observer callback and the
+       middle product is handed the stage and taken off it in the same tick, which
+       reads as skipping straight past it. Scroll still chooses the card; it just
+       can't take one away before it has been seen. A card is given the stage one at
+       a time and holds it for at least its own entrance, so a jump plays the beats it
+       crossed instead of discarding them. Ordinary scrolling never reaches this —
+       beats are further apart than the interval. */
+    const BEAT_MS = 400;
+    let shownTechnology = 0;
+    let pendingTechnology = 0;
+    let shownSince = 0;
+    let beatTimer = 0;
+
+    const playNextBeat = () => {
+      beatTimer = 0;
+      if (shownTechnology === pendingTechnology) return;
+
+      shownTechnology += pendingTechnology > shownTechnology ? 1 : -1;
+      showTechnology(shownTechnology);
+      shownSince = performance.now();
+      if (shownTechnology !== pendingTechnology) {
+        beatTimer = window.setTimeout(playNextBeat, BEAT_MS);
+      }
+    };
+
+    const activateTechnology = (index: number) => {
+      pendingTechnology = index;
+      if (beatTimer || shownTechnology === pendingTechnology) return;
+
+      const held = performance.now() - shownSince;
+      if (held >= BEAT_MS) {
+        playNextBeat();
+        return;
+      }
+      beatTimer = window.setTimeout(playNextBeat, BEAT_MS - held);
+    };
+
+    showTechnology(0);
 
     /* The fixed shell deliberately keeps the masthead and footer outside main's
        scrollport. Forward gestures that begin there (or in the shell gutter) into
@@ -1341,19 +1492,183 @@ const canonical = new URL('/', Astro.site);
       document.addEventListener('touchcancel', () => { touchY = null; }, { capture: true, passive: true });
     }
 
-    const stepObserver = new IntersectionObserver(
+    /* Where the band below reaches: the story hands over to a card when that card's
-      (entries) => {
+       box crosses this line. Kept in step with the rootMargin. */
-        entries.forEach((entry) => {
+    const bandBottom = () => (scrollRoot ? scrollRoot.clientHeight : window.innerHeight) * 0.62;
-          if (!entry.isIntersecting) return;
+
-          const index = Number((entry.target as HTMLElement).dataset.technologyStep);
+    /* Read against the measured offsets below rather than the live boxes. Same test —
-          if (Number.isInteger(index)) activateTechnology(index);
+       an offset is only that box's top with the line already subtracted — but it is
+       the observer's own crossing expressed as a scroll position, so the two cannot
+       land on either side of a fraction of a pixel and disagree about which card the
+       reader is on. It also costs no layout, which matters now that this is asked on
+       every scrolled frame and not only when a box crosses. */
+    const technologyAtScroll = () => {
+      const scrolled = scrollRoot?.scrollTop ?? 0;
+      let index = 0;
+      steps.forEach((_, stepIndex) => {
+        if (scrolled >= (beatEdges[stepIndex] ?? Infinity)) index = Math.max(index, stepIndex);
       });
-      },
+      return index;
+    };
+
+    const stepObserver = new IntersectionObserver(
+      /* Read the whole run of boxes rather than only the ones that changed. An entry
+         reports that a box crossed the band, not which side of the story the reader
+         is now on — scrolling back to the top, the opening box can pass the band from
+         above without ever entering it, and a stack driven by entries alone would sit
+         on a card the reader has already scrolled away from. The callback still does
+         the job it is here for: saying that something moved. */
+      () => activateTechnology(technologyAtScroll()),
       /* A wider center band advances the next card earlier, reducing the scroll
          distance between beats without changing the sticky composition. */
       { root: scrollRoot, rootMargin: '-38% 0px -38% 0px' },
     );
 
     steps.forEach((step) => stepObserver.observe(step));
+
+    /* The same line again, read as scroll offsets rather than as a test: where each
+       card takes the stage, and where the scroll runs out. The keyboard steps between
+       these and the progress track measures against them, so both agree with the
+       observer by construction instead of by a second set of numbers. */
+    let beatEdges: number[] = [];
+
+    /* One segment per card, built from the cards so the two cannot disagree. */
+    const beatBars = progressTrack
+      ? cards.map(() => progressTrack.appendChild(document.createElement('span')))
+      : [];
+    const beatFills = cards.map(() => -1);
+
+    const syncProgress = () => {
+      if (!scrollRoot || !beatBars.length) return;
+
+      const scrolled = scrollRoot.scrollTop;
+      beatBars.forEach((bar, index) => {
+        const start = beatEdges[index] ?? 0;
+        const span = Math.max(1, (beatEdges[index + 1] ?? 0) - start);
+        /* Three decimals is finer than a hairline can show and coarse enough that a
+           resting scroller stops writing to the DOM at all. */
+        const fill = Math.round(Math.min(1, Math.max(0, (scrolled - start) / span)) * 1000) / 1000;
+
+        if (beatFills[index] === fill) return;
+        beatFills[index] = fill;
+        bar.style.setProperty('--beat-fill', String(fill));
+      });
+    };
+
+    function measureBeats() {
+      if (!scrollRoot) return;
+
+      const end = Math.max(0, scrollRoot.scrollHeight - scrollRoot.clientHeight);
+      const rootTop = scrollRoot.getBoundingClientRect().top;
+      const line = bandBottom();
+
+      beatEdges = [
+        ...steps.map((step) => {
+          const offset = step.getBoundingClientRect().top - rootTop + scrollRoot.scrollTop - line;
+          return Math.min(end, Math.max(0, offset));
+        }),
+        end,
+      ];
+
+      syncProgress();
+    }
+
+    /* Halfway through the beat, not at its edge. A card is handed the stage at the
+       exact offset its box crosses the line, so landing there leaves the story one
+       pixel from giving it back. The opening and closing beats rest at the ends of
+       the scroll instead, where the page itself is the boundary. */
+    const beatRest = (index: number) => {
+      const end = beatEdges[beatEdges.length - 1] ?? 0;
+      if (index <= 0) return 0;
+      if (index >= steps.length - 1) return end;
+      return ((beatEdges[index] ?? 0) + (beatEdges[index + 1] ?? end)) / 2;
+    };
+
+    /* The hint has one job and does it once: any scroll at all is proof it has been
+       read, and it does not come back. An instruction that outlives its own need is
+       the obtrusive kind. */
+    let hintRead = false;
+
+    const readHint = () => {
+      if (hintRead) return;
+      hintRead = true;
+      progressHint?.classList.add('is-read');
+    };
+
+    if (scrollRoot) {
+      let progressFrame = 0;
+
+      scrollRoot.addEventListener(
+        'scroll',
+        () => {
+          readHint();
+          if (progressFrame) return;
+          progressFrame = requestAnimationFrame(() => {
+            progressFrame = 0;
+            /* The observer speaks only when a box crosses the band, which is enough
+               while a gesture keeps going and not enough when one ends: a scroll that
+               stops just the other side of a crossing gets no further callback, and
+               the story would sit on the card it was leaving. Every scrolled frame
+               asks instead. */
+            activateTechnology(technologyAtScroll());
+            syncProgress();
+          });
+        },
+        { passive: true },
+      );
+
+      /* Arrow keys move the story a beat at a time — the cards are the page's only
+         landmarks, and a keyboard nudge between two of them lands on nothing but a
+         composition that has not moved. main is the only scrollport and never takes
+         focus, so the document is where these have to be caught, for the same reason
+         the wheel and touch gestures are forwarded into it above. */
+      const KEY_BEAT_MS = 240;
+      const KEY_RUN_MS = 700;
+      let keyBeat = 0;
+      /* Not 0: performance.now() is measured from the page's own start, so a zero here
+         would read as "a beat just played" and eat the first key of a reader who
+         reaches for one before the clock has passed the pause below. */
+      let keyBeatAt = -Infinity;
+
+      document.addEventListener('keydown', (event) => {
+        if (event.defaultPrevented) return;
+        if (event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) return;
+
+        const direction = event.key === 'ArrowDown' ? 1 : event.key === 'ArrowUp' ? -1 : 0;
+        if (!direction) return;
+
+        const target = event.target as HTMLElement | null;
+        if (target?.isContentEditable) return;
+        if (target && /^(?:INPUT|TEXTAREA|SELECT)$/.test(target.tagName)) return;
+
+        /* Nothing else on this page scrolls, so the key belongs to the story whether
+           or not it arrives during the pause below. */
+        event.preventDefault();
+
+        const now = performance.now();
+        if (now - keyBeatAt < KEY_BEAT_MS) return;
+
+        measureBeats();
+        /* A key pressed while the last jump is still travelling counts from where
+           that jump was going, not from where the scroll has reached — read the
+           position instead and a held key stalls, re-deciding from a beat it has not
+           arrived at yet. Long enough after one, the scroll is the truth again. */
+        const from = now - keyBeatAt < KEY_RUN_MS ? keyBeat : technologyAtScroll();
+        keyBeat = Math.min(cards.length - 1, Math.max(0, from + direction));
+        keyBeatAt = now;
+
+        activateTechnology(keyBeat);
+        scrollRoot.scrollTo({
+          top: beatRest(keyBeat),
+          /* Read now rather than at load: the preference can be turned on with the
+             page already open, and this is the one piece of motion here that a
+             stylesheet cannot reach. */
+          behavior: reducedMotion.matches ? 'auto' : 'smooth',
+        });
+        readHint();
+      });
+    }
+
+    measureBeats();
   }
 </script>