perf(dashboard): place live EPG progress fills without layout or animation (#1721)

* perf(dashboard): slide live EPG progress fills with a compositor transform

The live-programme bars on channel rail cards and the hero animated their
width over 0.4 s whenever the 30 s live-EPG tick moved them. Width is a
layout property, so each tick re-laid out the whole document for about 24
frames, also while the window was minimized. Slide a full-width fill with
translateX driven by a --live-progress custom property instead; Chromium
runs that transition on the compositor. Reduced motion drops it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* test(dashboard): format the live progress spec

* perf(dashboard): stop animating the live EPG progress fills

A live-EPG tick moves the bar by under one percent, so the 0.4 s transform
transition was invisible but still produced a burst of compositor frames
on every tick. Place the fill without a transition.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* test(dashboard): pin the hero progress fill to its custom property

The hero moved into DashboardHeroComponent (#1738); its progress bar gets
the same transform fill as the rail cards.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: 4gray <fourgray@proton.me>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.changes/dashboard-live-progress-compositor.md

@@ -0,0 +1,8 @@
+---
+type: perf
+area: dashboard
+---
+
+Live programme progress bars on the dashboard now move without animating or
+redrawing the whole page, so a dashboard left open with recent live channels
+uses less CPU and GPU.

libs/workspace/dashboard/feature/src/lib/rails/dashboard-hero.component.html

@@ -141,7 +141,7 @@
                         aria-valuemax="100"
                         [attr.aria-valuenow]="slide.progress"
                     >
-                        <i [style.width.%]="slide.progress"></i>
+                        <i [style.--hero-progress]="slide.progress"></i>
                     </span>
                 }
 

libs/workspace/dashboard/feature/src/lib/rails/dashboard-hero.component.scss

@@ -339,10 +339,15 @@
 
     i {
         display: block;
+        width: 100%;
         height: 100%;
         border-radius: inherit;
         background: var(--app-selection-color, #78adff);
-        transition: width 0.4s ease;
+        // A full-width fill slid into place, neither a width nor animated: a
+        // live-EPG tick moves it by under one percent, so an animation was
+        // invisible yet cost a layout pass (width) or a burst of compositor
+        // frames (transform transition) on every tick.
+        transform: translateX(calc(var(--hero-progress, 0) * 1% - 100%));
     }
 
     &--live i {

libs/workspace/dashboard/feature/src/lib/rails/dashboard-hero.component.spec.ts

@@ -254,6 +254,19 @@ describe('DashboardHeroComponent', () => {
         ).toBe('/workspace/a');
     });
 
+    it('positions the progress fill through a custom property, never its width', () => {
+        // Animating width re-lays out the page on every live-EPG tick; the
+        // stylesheet slides the fill with a transform driven by this property.
+        slides.set([
+            { ...slide('a', 'Live'), contentType: 'live', progress: 42 },
+        ]);
+        render();
+
+        const fill = host().querySelector<HTMLElement>('.hero__progress i');
+        expect(fill?.style.getPropertyValue('--hero-progress')).toBe('42');
+        expect(fill?.style.width).toBe('');
+    });
+
     it('renders nothing when there is nothing to feature', () => {
         slides.set([]);
         render();

libs/workspace/dashboard/feature/src/lib/rails/dashboard-rail.component.html

@@ -126,7 +126,7 @@
                                     "
                                 >
                                     <i
-                                        [style.width.%]="
+                                        [style.--live-progress]="
                                             card.nowPlayingProgress ?? 0
                                         "
                                     ></i>

libs/workspace/dashboard/feature/src/lib/rails/dashboard-rail.component.scss

@@ -727,10 +727,15 @@
 
     i {
         display: block;
+        width: 100%;
         height: 100%;
         background: var(--app-live-color, #ff8f8f);
         border-radius: 2px;
-        transition: width 0.4s ease;
+        // A full-width fill slid into place, neither a width nor animated: a
+        // live-EPG tick moves it by under one percent, so an animation was
+        // invisible yet cost a layout pass (width) or a burst of compositor
+        // frames (transform transition) on every tick.
+        transform: translateX(calc(var(--live-progress, 0) * 1% - 100%));
     }
 
     &--idle i {

libs/workspace/dashboard/feature/src/lib/rails/dashboard-rail.component.spec.ts

@@ -335,6 +335,34 @@ describe('DashboardRailComponent', () => {
             expect(visible.at(-1)).toEqual(['a', 'b']);
         });
 
+        it('positions the live progress fill through a custom property, never its width', async () => {
+            // Animating width re-lays out the page for every frame of the
+            // transition on each EPG tick; the stylesheet slides the fill with
+            // a compositor transform driven by this property instead.
+            installObservers(false);
+            const { fixture } = await render([
+                card({
+                    id: 'known',
+                    contentType: 'live',
+                    nowPlayingProgress: 37.5,
+                }),
+                card({ id: 'unknown', contentType: 'live' }),
+            ]);
+            const fills = Array.from(
+                (
+                    fixture.nativeElement as HTMLElement
+                ).querySelectorAll<HTMLElement>('.rail__channel-progress i')
+            );
+            expect(fills).toHaveLength(2);
+            expect(fills[0].style.getPropertyValue('--live-progress')).toBe(
+                '37.5'
+            );
+            expect(fills[1].style.getPropertyValue('--live-progress')).toBe(
+                '0'
+            );
+            expect(fills.map((fill) => fill.style.width)).toEqual(['', '']);
+        });
+
         it('shows the placeholder only while a live card is pending its first answer', async () => {
             installObservers(false);
             const { fixture } = await render([