The scene stops heating the MacBook

"Terribly high CPU usage, the MacBook gets really hot" - a fanless MacBook
Air on a 144Hz screen. Measured on that machine with headed engines
(process CPU plus the per-process GPU time macOS keeps): an idle Aero
library cost LibreWolf ~110% CPU and ~230ms/s of GPU, the study feed ~130%,
Chromium up to ~57% CPU and ~350ms/s of GPU, Safari ~220-250ms/s of
WindowServer GPU. Priced one by one:

- the gradient mask on .ice-floats re-rendered the animated layer offscreen
  on every frame (~75 points of Gecko CPU). The floats now rise through a
  plain rectangular band clear of the header, the bottom chrome and the
  rail, and fade in and out inside it, so the clip never cuts a visible one;
- the overlay grain forced a backdrop readback per frame for a texture that
  measured a mean <=0.11/255 difference: removed;
- the invisible blob drift made every frame a full-screen redraw: the blobs
  are painted once;
- static glass (answer tiles, feedback panel, chips, inputs, dropzones,
  lists, segmented controls, Aero hint chips) re-blurred the moving scene
  every frame: only floating glass blurs now, and Aero's baked chat chrome
  drops a live blur that never showed under the bake;
- the scene also parks while the window has no focus and under any dialog
  or sheet scrim (.scene-pause); the loading icon is a compositor-run CSS
  animation instead of a framer-motion main-thread loop.

After, focused and animating: LibreWolf library 109% -> 33% CPU, study
134% -> 34%, chat 130% -> 42%; Chromium GPU 2.5-4.4x lower with 7-22 points
less CPU; Safari's WindowServer GPU -20-26% in Aero, about half in dark.
Unfocused or under a sheet: nothing. bubbles-test sweeps every float through
41 phases against the band and pins the parking and the cost contract;
tests/heat-probe.mjs (macOS) repeats the measurement; the suites find
Playwright's Chromium on macOS.

All 15 suites pass, lint clean, the contrast scan lost a finding. Version
0.6.7, SW v89.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/README.md

@@ -8,7 +8,8 @@ reboot cannot wipe the harness.
 
 - The app is running on `http://127.0.0.1:3207` (`systemctl --user start freezmo`).
 - A Chromium build. The suites auto-detect the newest Playwright Chromium in
-  `~/.cache/ms-playwright/`; override with `CHROME=/path/to/chrome`.
+  `~/.cache/ms-playwright/` (Linux) or `~/Library/Caches/ms-playwright/` (macOS);
+  override with `CHROME=/path/to/chrome`.
 - `npm install` (dev deps: `playwright-core`, `axe-core`).
 
 ## Running
@@ -27,7 +28,7 @@ prints a per-suite summary at the end.
 | Suite | Covers |
 | --- | --- |
 | `regression.mjs` | Library, deck card + menu, study feed to results, homework entry, desktop shell + settings/health panel. |
-| `bubbles-test.mjs` | Ice-scene bubbles: stacking/layout contract, keyframes only transform+opacity, rise/sway/scale/fade phases, per-breakpoint counts (5/3/2), phone pacing, reduced motion, tab-hidden parking. |
+| `bubbles-test.mjs` | Ice-scene bubbles: stacking/layout contract, the open band (a plain clip, no mask) and a 41-phase sweep that no visible orb or bubble ever touches its edges, keyframes only transform+opacity, rise/sway/scale/fade phases, per-breakpoint counts (5/3/2), phone pacing, reduced motion, parking (hidden tab, unfocused window, dialog scrim), and the cost contract (static blobs, no blend-mode grain, no blur on static glass, no hidden blur under Aero's bake). |
 | `mobile-test.mjs` | Five-tab bar at 360/390 × EN/CS × dark/light × reduced motion (labels, targets, no hamburger/drawer), the library ⋯ sheet (Import JSON / New folder), the settings sheet (touch targets, key flow, drag-to-close, backdrop), axe contrast audits. |
 | `wizard-test.mjs` | Deck 3-step flow and homework flow, flat action bar, in-page mode switch, the loading lock, abort-on-leave. |
 | `native-test.mjs` | Manifest/PWA head, offline banner + disabled generate, share target GET + POST, Back-gesture layers, undo toast, tab re-tap, haptics, draft restore. |
@@ -53,3 +54,10 @@ leak between suites. Scratch data for the VAPID test lives in `tests/.tmp/`
 CDP performance trace (rAF frame timing, long tasks, main-thread busy time,
 style recalcs) on a 4× throttled phone profile and a 2× desktop profile. It
 always exits 0; the numbers are for tuning the bubble count/speed.
+
+`node tests/heat-probe.mjs [webkit|chromium]` (macOS only) measures what an
+idle screen actually costs the machine: headed Playwright WebKit and Chromium
+on the real display, the browser's CPU, the GPU time of its processes and of
+WindowServer, per screen and theme, against an `about:blank` baseline and with
+the scene parked. Install the engines once with
+`npx playwright-core install webkit chromium` and keep the window in front.