the periscopes never built on this machine: bounded idle gate, and the fog rides the scroller's timeline instead of chasing it

THE HEADLINE, and it invalidates a lot of earlier reasoning about the glass
bar: all three periscopes were gated on an idle callback granting a >=15ms
slice, and with any frame continuously pending this 60Hz laptop caps
timeRemaining at ~13.5ms. The gate NEVER passed — traced hundreds of
consecutive refusals — so the fog never built, on any pane, all session. What
the bar had been showing all along was no fog at all: a thin tint over the raw
page. That is why Kyle read the top bar as "so light compared to the left and
right sidebar" (on album pages the raw page there is the banner, deliberately
bled up bright), and why the Now Playing blur "goes away whenever the next
track plays and its glitchy" — every track change clears that pane's fog for
rebuild, and the rebuild starved forever. The skip is now bounded: after eight
starved retries (~1-2s of honest waiting) it builds anyway. Same three lines in
GlassBar, Sidebar and NowPlaying — the pattern is copied, so a fix to one is
not a fix.

THE BAND'S TINT, once there was a fog to judge. The bar wore
rgba(20,20,24,0.28): a non-black colour that adds ~6 luma of its own light, at
a net 0.676 against the panes' 0.7075, so it read lighter than the panes by
construction. It now wears the panes' exact frost — pure black 0.35 over the
0.55 canvas — applied as .peri::after, because the bar's own background paints
UNDER .peri and cannot tint the fog (measured: an 0.85 background moved the
band 34.6 -> 33.5). Same material as the sidebar and Now Playing bands;
brightness then follows the wallpaper for all of them alike, which is why they
measure 20-36 across one screen and no absolute number could have matched.

THE FOG RIDES THE COMPOSITOR NOW. It chased scroll events on the main thread
and landed frames late ("the content behind the glass bar is delayed with
scrolling"). .pane-shell publishes the scroller as a named timeline
(--pane-scroll) and the clone animates against it, so the ride equals -scrollTop
with the main thread nowhere in the loop. Verified as a live ScrollTimeline
animation tracking scrollTop exactly. The rules live in global.css on purpose:
Svelte's -global- keyframes prefix stripping desynced animation-name from
@keyframes when they lived in the component, and getAnimations() showed it dead.
The old event sync stays as the no-timeline-support fallback.

THE SEARCH WASH reaches the top of the bar again. Its contract is that "the bar
frosts over colour rather than over black", but the frost veil dimmed the whole
fog and left a dark step where bright wash met the band; and the blur kernel at
the band's top edge sampled past the wash's own top edge into nothing, fading
the colour out over the first ~20px — the dark strip Kyle photographed twice.
The cloned wash is boosted to compensate for the veil exactly, and bled into the
fog's 48px overscan so the kernel always has colour to sample. The album banner
never showed this because its box already bleeds -70px above the page.

Judged on OS-level captures throughout (CopyFromScreen): CDP screenshots cannot
see the acrylic and led every wrong turn in this file's history. 98/98 tests.

src/App.svelte

@@ -309,6 +309,11 @@
            artwork behind the bar (search) has to start below it, or its first
            heading sits under the frost at rest. */
         --bar-h: 46px;
+        /* Publishes the scroller's timeline to the glass bar's fog, which
+           is a SIBLING of the scroller — the fog's ride animates against
+           this instead of chasing scroll events on the main thread (the
+           chase lagged visibly on the 60Hz laptop; see GlassBar). */
+        timeline-scope: --pane-scroll;
     }
 
     .content {
@@ -323,6 +328,11 @@
            away with the content, keeping the seam colors identical at every
            scroll position. */
         background-attachment: local;
+        /* The named timeline the fog rides (scope on .pane-shell above).
+           The artist page overwrites this with its own INLINE
+           scroll-timeline for its hero rides — that page is painted, has
+           no fog, and needs no pane timeline. */
+        scroll-timeline: --pane-scroll block;
         overflow-y: auto;
         overflow-anchor: none;
         /* Main scroll pane: no elastic rubber-band at its edges. Inner regions