An iOS-style focus pull: the thing arrives out of focus and the blur fades
off it as the opacity comes up. Opacity leads the blur (full opacity around
45%, blur still lifting), which is what separates it from a cross-fade.
Ships on tabs (440ms), agent windows (560ms), the terminal pane (520ms) and
connection lines (380ms), plus a `Soft focus` theme that sets all four.
Default stays `legacy`, so an untouched install is unchanged.
The terminal pane is the one surface that cannot blur itself the documented
way, and `blur` takes a deliberate exception to the "never a filter on
.terminal-container" rule. Every alternative was measured against a live
xterm and does not work: a backdrop-filter veil on ::before blurs perfectly
while STATIC, and Chrome silently drops the backdrop the moment ANY
animation runs on that pseudo-element (the veil computes blur(15.3px) while
the text behind it stays razor sharp); driving the radius from rAF buys the
same full-screen blur per frame plus main-thread work. The cost the rule
exists to avoid is inherent to blurring a terminal, so the style buys it
knowingly: opt-in, off by default, one ~520ms run per session open, class
straight back off, will-change still unset. Worst-case price, headless
SwiftShader with no GPU: frame deltas 16.7ms -> 33.3ms for the run, against
16.7ms flat for `fade`. cols x rows measured unchanged at 178x38 before,
during and after, so FitAddon never sees it.
The line entrance animates `filter` too, where each line already carried
its glow. Both kinds now hold it in --line-glow and both keyframes say
`blur(N) var(--line-glow)`, so the function lists match and interpolate
instead of the glow vanishing for the run and popping back (a lineage
line's glow is a different colour, set per element). Its 100% frame omits
`opacity` on purpose so the endpoint comes from the element's own resting
value: 0.9 subagent, 0.72 lineage, 0.95 working.
test/entrance-animations.test.ts is a new static guard over the whole
feature, not just this style: the rule -> keyframes -> theme-option chain a
style silently does nothing without, the terminal's paint-only property
allowlist (the FitAddon rule), the --line-glow contract, and reduced-motion
coverage. Mutation-checked both ways.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
