The battery pass: paint less, wake less

- opaque canvas: the compositor stops alpha-blending 2.5Mpx at 60Hz
- settled modals and the death summary idle at 20-24 fps; play untouched
- TUNE.lowPower caps RES at 3 (-44% pixels/frame), flippable live

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

HANDOFF.md

@@ -442,6 +442,22 @@ the countdown panel ('CHANGEOVER · RESUMING IN n'). He kept the burst-arm weapo
 praise words. **A bottom/above-rack message slot was proposed and REJECTED**: that is thumb
 territory — covered by the hand mid-pull and outside where the eyes are.
 
+**Fifth batch, same day — THE BATTERY PASS.** "Drains battery like there is no tomorrow." Measured
+first: update() 0.01 ms, render() 0.15 ms per frame — the JS is nothing. The bill is fill-rate ×
+frame-rate (a 3x iPhone pushes a ~1080×2400 canvas through the compositor 60×/s) plus 60 Hz wakeups
+on static screens. Three levers shipped:
+- **The canvas is OPAQUE now** (`dom.js`: `getContext('2d', {alpha:false, desynchronized:true})`)
+  — render() clears the whole frame to a solid colour anyway, so the compositor no longer alpha-
+  blends 2.5 Mpx sixty times a second. Free.
+- **Calm states run slow** (`calmFps()` in main.js): a SETTLED modal (world frozen, only the blink
+  moves) runs at 20 fps, the death summary once faded at 24. Live play stays at TUNE.fps — the 60
+  was a feel decision and the governor deliberately never touches anything that moves.
+- **`TUNE.lowPower`** (>= 0.5, T-panel-flippable live): caps RES at 3 — −44% of pixels painted per
+  frame, THE big lever. `RES` is `export let` now, re-derived in fitViewport; main.js re-fits when
+  the knob flips. Sprites are 224px sources so RES 3 draws them at-or-below 1:1: softer, never
+  mushy. OFF by default — whether the sharpness trade is worth it is Oliver's phone-call, and if he
+  wants it player-facing it should become a settings toggle, not a TUNE knob.
+
 **Fourth batch, same day — the card went HORIZONTAL, and nothing draws under a modal.** The
 stacked icon card ran 102 px tall and its lower third hung over live court; the icon sits LEFT of
 the text now (boxed to 58×52 so a wide tin cannot reach the type — and it draws BIGGER than the