PCO Plan 1.8.0: the plan follows AbleSet, and auto-scroll stays in its tile

Three things, the first on its own.

**Auto-scroll moves the tile, not the board.** `scrollIntoView` walks up and
scrolls every ancestor that can scroll, so bringing the current item into
view dragged the whole dashboard with it whenever the board was taller than
the window. The list's own `scrollTop` is moved instead, measured from
rectangles because the rows' offset parent is the tile rather than the list.

**The current item fills as its song plays.** When an AbleSet module is
installed, configured and playing a song that IS the item on screen, that
item's background fills left to right with the song. The song is tied to a
plan item by the same name matching the live ProPresenter document already
uses, so a bar can never quietly fill the sermon while the band rehearses
something else.

**Its sections slide past, bottom right of that item.** Every section of the
song as a strip, the played ones dimmed, the one playing filling in turn and
kept centred — by moving that strip's own `scrollLeft`, for the same reason
as above. The chips are rebuilt only when the song changes; moving to the
next section just moves the classes, so the strip keeps its place.

Both are switches in the tile's gear, **Song progress** and **Song
sections**, and both draw nothing at all unless there is an AbleSet module
to follow: the server reports `available: false` for no module, a disabled
one, or one with no host, and re-checks every 15 s so installing AbleSet
later lights it up without a restart.

The server follows the AbleSet module over loopback exactly as it follows
ProPresenter's, and republishes a small slice — song, sections, playhead in
beats with a stamp — as its own `ableset` SSE event. Its own event because
it moves five times a second and must never drag the plan (items, teams)
onto the wire with it; the tile carries the playhead forward from the tempo
between packets.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

modules/pco-plan/client.js

@@ -34,6 +34,7 @@ function createPlan({ root, moduleApi }) {
   let ticker = null;
   let lastCurrentId = null;
   let lastListKey = '';
+  let absView = null;         // what the server says AbleSet is doing, if anything
   let userScrolledAt = 0;
 
   root.innerHTML = `
@@ -493,6 +494,133 @@ function createPlan({ root, moduleApi }) {
     renderLiveMarks();
   }
 
+  /* ── AbleSet: the song playing under the current item ──────────────
+     Everything here draws only when the server says there is an AbleSet
+     module, it is configured and reachable, and the song it is playing is
+     the plan item on screen. Any of those missing and the tile looks
+     exactly as it did before AbleSet existed. */
+
+  /** The playhead now, in beats, carried forward from the last packet. */
+  function absBeatsNow() {
+    if (!absView || absView.beats == null) return null;
+    if (!absView.playing || !absView.tempo) return absView.beats;
+    const since = Math.max(0, serverNow() - absView.at) / 1000;
+    return absView.beats + since * (absView.tempo / 60);
+  }
+
+  function absFraction(part) {
+    const beats = absBeatsNow();
+    if (beats == null || !part || part.start == null || part.end == null) return null;
+    const span = part.end - part.start;
+    if (!(span > 0)) return null;
+    return Math.max(0, Math.min(1, (beats - part.start) / span));
+  }
+
+  /** The row AbleSet's song belongs to — only ever the current one. */
+  function absRow() {
+    const a = absView;
+    if (!a || !a.available || !a.reachable || !a.song || !a.itemId) return null;
+    if (a.itemId !== lastCurrentId) return null;
+    return listEl.querySelector(`.pp-row[data-id="${CSS.escape(a.itemId)}"]`) || null;
+  }
+
+  /** Keep the playing section visible in the strip — this strip, nothing else. */
+  function absScrollSections(strip) {
+    const active = strip.querySelector('.pp-abs-sec.is-now');
+    if (!active) return;
+    const box = strip.getBoundingClientRect();
+    const rect = active.getBoundingClientRect();
+    const delta = (rect.left - box.left) - (strip.clientWidth - rect.width) / 2;
+    if (Math.abs(delta) < 1) return;
+    strip.scrollTo({ left: strip.scrollLeft + delta, behavior: 'smooth' });
+  }
+
+  function renderAbleSet() {
+    const row = absRow();
+
+    // Anything left on a row that is no longer the one goes.
+    for (const stale of listEl.querySelectorAll('.pp-fill, .pp-abs-sections')) {
+      if (!row || !row.contains(stale)) stale.remove();
+    }
+    if (!row) return;
+
+    if (on('absProgress')) {
+      const fraction = absFraction(absView.song);
+      if (fraction == null) {
+        row.querySelector('.pp-fill')?.remove();
+      } else {
+        let fill = row.querySelector('.pp-fill');
+        if (!fill) {
+          fill = document.createElement('div');
+          fill.className = 'pp-fill';
+          row.prepend(fill); // behind the row's content, which the stylesheet lifts
+        }
+        fill.style.width = `${(fraction * 100).toFixed(2)}%`;
+      }
+    } else {
+      row.querySelector('.pp-fill')?.remove();
+    }
+
+    if (on('absSections') && absView.sections.length) {
+      const main = row.querySelector('.pp-col-main');
+      let strip = row.querySelector('.pp-abs-sections');
+      if (!strip && main) {
+        strip = document.createElement('div');
+        strip.className = 'pp-abs-sections';
+        main.appendChild(strip);
+      }
+      if (strip) {
+        // The chips are rebuilt only when the song's sections change. Moving
+        // on to the next section just moves the classes: rebuilding would
+        // throw the strip's scroll away thirteen times a song.
+        const key = absView.sections.map((s) => s.name).join('\u0000');
+        if (strip.dataset.key !== key) {
+          strip.dataset.key = key;
+          strip.dataset.now = '';
+          strip.innerHTML = '';
+          for (const section of absView.sections) {
+            const chip = document.createElement('span');
+            chip.className = 'pp-abs-sec';
+            chip.textContent = section.name;
+            strip.appendChild(chip);
+          }
+        }
+        const now = absView.section?.index ?? -1;
+        if (strip.dataset.now !== String(now)) {
+          strip.dataset.now = String(now);
+          [...strip.children].forEach((chip, i) => {
+            chip.classList.toggle('is-now', i === now);
+            chip.classList.toggle('is-done', i < now);
+            if (i !== now) chip.style.removeProperty('--pp-sec-fill');
+          });
+          requestAnimationFrame(() => absScrollSections(strip));
+        }
+        const active = strip.children[now];
+        if (active) {
+          const fraction = absFraction(absView.section);
+          active.style.setProperty('--pp-sec-fill', fraction == null ? '0%' : `${(fraction * 100).toFixed(1)}%`);
+        }
+      }
+    } else {
+      row.querySelector('.pp-abs-sections')?.remove();
+    }
+  }
+
+  /**
+   * Centre a row in this tile's own list. `scrollIntoView` would walk up and
+   * scroll every ancestor that can scroll with it, which on a dashboard taller
+   * than the window drags the whole board; moving `listEl.scrollTop` moves
+   * this tile and nothing else. Measured from rectangles rather than
+   * `offsetTop` because the rows' offset parent is the tile, not the list.
+   */
+  function keepInView(row) {
+    const list = listEl.getBoundingClientRect();
+    const rect = row.getBoundingClientRect();
+    const delta = (rect.top - list.top) - (listEl.clientHeight - rect.height) / 2;
+    if (Math.abs(delta) < 1) return;
+    listEl.scrollTo({ top: listEl.scrollTop + delta, behavior: 'smooth' });
+  }
+
   /** Current / done classes and the elapsed timers, without rebuilding rows. */
   function renderLiveMarks() {
     const live = state?.live || {};
@@ -531,11 +659,12 @@ function createPlan({ root, moduleApi }) {
       }
       if (!h.endedAt) elapsedEl.classList.add('is-running');
     }
+    renderAbleSet();
     if (currentId !== lastCurrentId) {
       lastCurrentId = currentId;
       if (currentId && tilePrefs().autoScroll !== false && Date.now() - userScrolledAt > 8000) {
         const row = listEl.querySelector(`.pp-row[data-id="${CSS.escape(currentId)}"]`);
-        row?.scrollIntoView({ block: 'center', behavior: 'smooth' });
+        if (row) keepInView(row);
       }
     }
   }
@@ -610,6 +739,7 @@ function createPlan({ root, moduleApi }) {
   }
 
   function tick() {
+    renderAbleSet();
     if (!state?.plan) return;
     renderClock();
     if (state.live?.following && on('showItemRuntime')) renderLiveMarks();
@@ -621,6 +751,7 @@ function createPlan({ root, moduleApi }) {
     if (!payload || typeof payload !== 'object' || !payload.state) return;
     state = payload.state;
     if (Number.isFinite(payload.now)) skew = payload.now - Date.now();
+    if (payload.ableset) absView = payload.ableset;
     feedOffline = false;
     render();
   }
@@ -641,6 +772,16 @@ function createPlan({ root, moduleApi }) {
             accept(JSON.parse(ev.data));
           } catch { /* a bad frame is not fatal */ }
         },
+        // Its own event, several a second while a song plays: redraw that one
+        // row rather than the whole list.
+        ableset(ev) {
+          try {
+            absView = JSON.parse(ev.data);
+          } catch {
+            return;
+          }
+          if (state) renderAbleSet();
+        },
       },
     });
   }