The reference shows a skeleton while loading and never paints cached rows
first, and its comments present that as the design. It is not: the instant
paint existed during development and was removed because it GLITCHED -
results visibly jumped between the cached paint and the fresh one. The
owner's reading is that the glitch was a Slint rendering problem rather than
something inherent to stale-while-revalidate, so it comes back here as a
reversible experiment: DEFAULT ON, with a ui_prefs opt-out
(cortinilla_instant_paint) that needs no rebuild to flip. The skeleton path
stays fully implemented as both the opt-out target and the cold-miss path.
What is cached is the FINISHED payload, not the API response. Reviving the
existing CAPA A result cache would have left the expensive half on the table:
a cortinilla payload is the response AFTER ranking, truncation, i18n titles,
the top-result pick and - the part no API cache can shortcut - the local
library query and its derived grouping.
qbz-app gains a generic PayloadCache<T>. The store never inspects T, which is
what lets both frontends share it despite their payload types having diverged
(one raw artwork_url vs an art_url/art_path pair). In-memory only: process
lifetime IS the TTL, because a payload embeds local rows and resolved artwork
paths and a persisted entry would resurrect albums the user has deleted.
Four properties are what should keep it from glitching, and each is a real
constraint rather than a hope:
- Same shape in both paints. The entry is written AFTER the local sections
are appended, so there is no mid-apply reflow left to see.
- Equality-gated replacement. CortinillaData derives PartialEq, so an
unchanged repeat query produces ZERO second paint.
- The selection survives - the publish path never writes selectedIndex.
- The scroll survives - C5's contentY latch. Without it the second paint
yanks the user to the top, which is the glitch by another name.
There are exactly TWO write points, and the placement is load-bearing: after
pass-1 artwork resolution, and again at the pass-2 republish once downloaded
covers land. Writing earlier caches rows with empty art_path, and since the
QML draws art_path only, a hit would paint cover-less rows AND the gate would
fire on every hit - the exact repaint this exists to avoid.
Invalidation: bound per session, dropped on logout, and cleared from
reload_browse - the single chokepoint every local-library mutation passes
through, since there is no library-changed signal to subscribe to.
Also fixes the immersive skeleton's scope bug, which is the twin of the one
C4b fixed on the desktop and which I missed there: a Timer derives from
QtObject, which has no parent property, so the unqualified parent resolved
out of the block entirely - the timer ran forever, pulse never changed, and
the skeleton never pulsed. Found by qmllint, not by reading. It picks up the
reduceMotion tick with the fix.
Contract: qbz-nix-docs/qt-frontend/2026-08-03-cortinilla-parity, commit C11
(section 5.c, rulings R1/R6, R7-10).
Gate: build clean, 258/258 tests + 2 new in qbz-app, both QML audits OK,
qmllint clean on both cortinillas, offscreen smoke 0 complaints + home
published.
cc
vicrodh
b38b0b3d57