Animate a home battery bank's charge and top-off curve in one self-contained HTML file

# Animate a home battery bank's charge and top-off curve in one self-contained HTML file Make a small animated scene: a home battery charge and top-off. Write one file, `out/scene.html`, that works opened straight from disk with no network access. `spec.json` gives the page title, the stage size and the scene parameters. **Looks are not scored**: the page is opened in a headless browser (800x600 window, UTC time zone, network blocked) and checked by objective tests only. ## Scene contract - Draw the scene on one `<canvas>` or `<svg>` stage of `width` x `height` CSS pixels (spec.json), visible on load, with `<title>` containing spec.json `title`. - Animate continuously from load (`requestAnimationFrame` or timers); no click is needed unless stated below. - Expose `window.sceneState()`, returning the scene's current state in stage pixel coordinates (origin top-left of the stage): `{batteries: [{name, x, y, level, status: "idle" | "charging" | "topping_off"}, ...]} (canvas px, y down; one entry per spec.json battery; x = the battery's centre; level = the charge height in px; y = the top of the charge, base_y − level)`. Extra fields are fine. It must describe what is actually drawn. - Time 0 is `performance.now()` 0 (seconds = `performance.now()` / 1000). Each battery sits at level `level0_px` until its own `charge_s`; it then charges at a steady `rate_px_s` (pixels of level per second) until the level reaches `cv_px`, which happens at tc = charge_s + (cv_px − level0_px) ÷ rate_px_s; after that the charger tapers off and the level is cv_px + (full_px − cv_px) × (1 − e^(−(time − tc) ÷ tau_s)), approaching but never passing `full_px`. The top y is `base_y` − level. Draw each battery and its charge. `sceneState()` must return the state at the moment it is called. - The page must log no errors and throw no exceptions. Keep the file at most 200,000 bytes; no external scripts, fonts, images or URLs (inline everything). ## Checks (partial credit = share passed) 1. `self_contained`: `out/scene.html` exists, is at most 200,000 bytes, references no http(s) or protocol-relative URL, and requests nothing from the network when opened. 2. `has_canvas_or_svg`: a visible `<canvas>` or `<svg>` of at least 300x200 CSS pixels is on the page. 3. `frames_change`: over 3 s, some later screenshot differs from the first in at least 0.1% of pixels, and at least 3 of 30 screenshots differ. 4. `charge_level`: at every sample more than 0.05 s from a battery starting to charge or reaching `cv_px`, each battery's x is within 1.5 px of its spec.json `x`, and its level and top y are within 1.5 px of the exact values: `level0_px` before `charge_s`, then rising at `rate_px_s` until it reaches `cv_px`, then cv_px + (full_px − cv_px) × (1 − e^(−s ÷ `tau_s`)) with s = seconds since it reached cv_px. 5. `battery_status`: at those samples each battery's `status` is idle before `charge_s`, charging until it reaches `cv_px`, then topping_off; the samples include all three statuses. 6. `no_console_errors`: no uncaught exception, `console.error` or browser error is logged during the run. ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.