[devin-ai-integration]

Summary

Six abrupt state changes now animate with the app's existing motion vocabulary (ease_out_quint, MOTION_IN_MS/MOTION_OUT_MS/MOTION_HOVER_MS, Presence, hover_bg). Everything honors cx.reduce_motion() by snapping to the end state.

• Focus-mode chrome: render_tabs now returns an element whose height (34→0) and opacity collapse in the same 280ms with_animation keyed on sidebar_gen as the sidebar slide — previously the strip returned None and vanished in one frame while the sidebar kept sliding.
• Focus dimming: LiveEditor keeps a DimFade { cur, prev, at }; RunStyle::dim_runs computes a per-line dim_amount (out of prev → out of cur, eased) and lerps each run toward pal.muted, requesting frames until t=1. Lines re-entering the block fade back.
• Programmatic scroll: Layout gained a glide flag; prepaint steps layout.scroll halfway toward the autoscroll target and repaints until <0.5px — the same pattern as the caret glide. The wheel path still writes scroll_y directly and clears autoscroll, so trackpad scrolling stays 1:1.
• Tabs: pill/close hovers use hover_bg; new pills fade in via with_animation(("tab-in", id)); closing a tab pushes a ClosingTab ghost (capped at 8) that renders at its old index and fades out over MOTION_OUT_MS while siblings hold position until the fade ends; the unsaved dot fades via Presence. (Said ghost approach means closed-tab fade-out IS mounted — no instant removal needed.)
• Text width: set_max_col seeds col_anim (from, to, at) (from the current eased value when retargeting mid-flight); prepaint eases max_col and requests frames while running.
• Theme: apply_theme in spaces_ui.rs captures the old Palette, applies the target via theme::apply, then sets the old global back and spawns a task lerping cx.set_global(theme::lerp(&from,&to,t)) + cx.notify() each ~16ms until done — no render-site edits needed. theme::lerp is a channel-wise u32 lerp (3-channel for rgb, 4-channel for rgba fields) with a unit test.

GUI verification (macOS, release build)

Verified live in the app with 60fps capture; every transition shows multi-frame intermediate states (not one-frame snaps).

Focus mode — sidebar slide + tab-strip collapse together; dim fades on caret moves; typewriter recenter glides:

Tabs — pill fades in on open; closed pill leaves a fading ghost while siblings hold position:

Theme crossfade — palette lerps over ~160ms (mid-fade is visibly mixed):

Light	Mid-fade	Dark

Also verified live: find-next scroll glides with an asymptotic tail while wheel scrolling steps discretely 1:1; Settings → Text width glides the column; the unsaved dot fades in with the dirty state.

Notes for reviewers

• RunStyle now takes fade_from/fade_t alongside focus; dimmed() was replaced by the eased dim_amount().
• A plain sidebar click retargets the current tab (open_path); Cmd+click opens a second tab — pre-existing behavior, unrelated to this PR.
• Reduced-motion snap is code-gated at every site but was not toggled live (macOS accessibility flag doesn't reliably propagate to a running process).

Link to Devin session: https://app.devin.ai/sessions/308b6c12ce7b420588973691e7035d63
Open in Devin Desktop: https://app.devin.ai/desktop/session/308b6c12ce7b420588973691e7035d63?variant=devin
Requested by: @horizzon3507

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring