The e2e measured the reserved band but never the symptom the change is
named for. Headless chromium defaults to an overlay scrollbar, which is
the configuration where a bar can cover row content at all, so the
scenario already ran in the right mode: against clean master the band is
0 and the bar covers 7px of the relative time.
Adds timeCoveredBy, the overlap between the relative time's right edge
and the range the bar occupies, taking the bar's width from the sheet
where it applies and from the UA's overlay width otherwise. Assuming 0
there would report no occlusion in precisely the state that has it.
Keeps the band assertion rather than replacing it: the two catch
different regressions. Removing only scrollbar-gutter leaves
timeCoveredBy at 0, because the bar is then 8px and the row's right
padding is also 8px, so it abuts the timestamp without covering it.
Removing the pseudo-element width as well is what produces the overlap.
Each was mutation-checked with the other assertions in its test silenced.
Records in the note that the gutter and the ::-webkit-scrollbar width are
jointly necessary against an overlay bar, measured by deleting each from
the live cascade with the other in force: either alone drops the band
from 8 to 0.
A non-`auto` `scrollbar-width` or `scrollbar-color` makes Chromium and Safari
discard every `::-webkit-scrollbar*` rule for that element, including
`::-webkit-scrollbar-thumb:hover`. Declaring both unconditionally left the
hover tokens rendering nowhere: the engines implementing the hover
pseudo-element are exactly the ones the standard properties silence, and
Firefox has no hover pseudo-element to fall back on. Both hover tokens and all
four elevated surfaces' hover rebinds were therefore dead code.
Measured in chromium on probe elements with `scrollbar-gutter: stable`: an 8px
`::-webkit-scrollbar` alone reserved a 30px band, and adding
`scrollbar-width: thin` dropped it to the 10px `thin` reserves.
The standard properties now sit inside `@supports not
selector(::-webkit-scrollbar)`, so Firefox takes them and WebKit-based engines
take the pseudo-elements. The WebKit rules stay ungated: an engine without
those pseudo-elements drops them as unknown selectors, and gating them would
hide them from an engine that implements them without `selector()` — the
pre-16.4 Safari the ungated form serves correctly.
Three unit assertions pin the split by source offset, which the existing
at-rule-flattening parser cannot see. The web e2e now reads the path chromium
actually takes: the `auto` standard properties as the gate's signature, the
pseudo-element sizing and track, the indirection variables resolved per
throwaway probe, and the hover declaration as cascade rule text — chromium
folds the `:hover` rule into `getComputedStyle(el,
'::-webkit-scrollbar-thumb')`, so no computed query separates the states.
Review follow-ups: the three new notify loops (currentProvideInfo
subscribers, ui-skill lexicon listeners, late-registration controller
setup) now contain per-callback failures so one faulty consumer cannot
starve the rest, abort the list projection pass, or poison the source
roster with no disposer; controller lexicon polling drops a throwing
source with a console record like the candidate path. The ui-slash
README (both languages) now states the late-registration warm and the
subscribeLexicon contract, and the scenario suite drives a typed /name
token gaining its decoration when the roll settles with no further
input.
provideInfo(id)/maybeProvideInfo(id) lost their last external caller
when the renderer host switched to the currentProvideInfo observable;
both become private (tests assert through the public projection). The
reprojection method's name now says what it does — re-derive and
publish on change — and matches the field family it maintains.
