635「하루의 끝」 — 새벽, 한낮, 노을, 밤이 한 바퀴 돌며 한 줄 시가 흐르는 14초 끊김 없는 루프

Make a short vertical looping film as one self-contained HTML file and render it to MP4. The idea: one whole day in one loop. Over a row of rooftop silhouettes the sky goes from dawn to bright noon to sunset to night and back to dawn; the sun crosses in a big arc, the moon follows it, stars come out, windows light up one by one at night and go dark before dawn, and one line of a short poem rises for each part of the day. The last frame is the first frame, so it can play forever. It must feel calm and warm, like a beautifully made ambient title. Do the whole job now without asking questions.

[Inputs (use the default when empty)]
Name: "【이름】" — default 프롬프트판 (shown small at the bottom the whole time)
Four poem lines for dawn, noon, sunset and night (slash-separated): "【시 4줄】"
Palette: "【색 조합】" — sky gradients (horizon → top) for dawn, noon, sunset, night:
  기본 = #F7B6A0→#9EB6E8, #8FD0FF→#DDF2FF, #FF8A5B→#5B3E8C, #0E1430→#26305E; windows #FFD27A
  파스텔 = #FFD1DC→#CDE3FF, #BFE6FF→#F2FBFF, #FFB7A1→#B39DDB, #2B2A4A→#4A4675; windows #FFE5A0
  흑백 한 점 = #D8D8D8→#9A9A9A, #F2F2F2→#CFCFCF, #8A8A8A→#3A3A3A, #151515→#2A2A2A; windows #FF5A3C (the one color)
Tempo: "【박자】" — default 100 BPM; one part of the day lasts 6 beats. Aspect ratio: Output size 1080x1920 pixels, 9:16 portrait story. Keep all text inside the central 80% of the height: compress every zone percentage below into the 10-90% range. (default 9:16).

[Everything is a function of the day phase]
Let p = (time / duration) mod 1, from 0 (dawn) to 1 (dawn again). Every value — sky colors, sun and moon positions, star twinkle, cloud drift, window lights, poem lines, the gentle camera breathing — must be a periodic function of p, so the frame at p = 1 is exactly the frame at p = 0. Blend the four sky gradients smoothly in order and back to the first. Night depth rises after sunset and fades out before dawn, with the same value at p = 0 and p = 1.
- Sun from p = 0 to 0.64 along a large arc from the left horizon to the right, warm white at noon and orange near the horizon, with a soft glow; moon from 0.6 to 1 along the same arc.
- Stars only at night, twinkling at whole-number multiples of the day frequency.
- A few soft clouds that drift exactly one full loop per day; white by day, dusky blue at night.
- Rooftop silhouettes (some pointed roofs, one tower) across the bottom third; each window has its own switch-on moment, so they light up one by one as night deepens, with a small warm glow.
- A dark street below with faint reflected light streaks.

[Poem]
Each line rises letter by letter from a mask line in the upper third during its quarter of the day and slides up out before the next one, in a serif face; dark ink by day, white at night, so it is always readable.

[Always-on details]
No timecode, no progress bar, no corner labels, no HUD. Light film grain. Typefaces: Nanum Myeongjo 800 for the poem and the name, from Google Fonts. Keep a 6% safe margin. Nothing ever freezes — the sky, clouds and lights are always moving a little.

[Sound]
If you can generate music, add a calm ambient loop at the given tempo (soft piano and pad, birdsong at dawn, crickets at night) that loops seamlessly with the picture, muxed into the MP4 as AAC. If you cannot generate audio files with a music model, write the backing track yourself in code instead: synthesize an original instrumental (kick, snare, hi-hats, bass, a chord pad and a light arpeggio, no vocals) at the given tempo with a simple chord loop, sample by sample into a WAV, then mux it into the MP4 as AAC. Never use a placeholder or someone else's recording.

[Build]
One HTML file, everything on a single canvas. The script starts with a `const CONFIG` object holding every input plus fps 60, a seed and loop true. All drawing comes from a pure `seek(t)` — no timers, no CSS animation, randomness only from the seed — so any frame renders identically. A settings panel above the preview (hidden with ?render=1) with Korean labels: a text input for the poem lines (slash-separated), selects for palette, tempo and ratio, play/pause, a scrubber, and a "설정 복사" button that copies CONFIG as code. Edits re-render instantly.
Write render.mjs: open the page with ?render=1 in headless Chromium (Playwright), wait for document.fonts.ready, step seek(frame / 60) through every frame of [0, duration) without repeating the end frame, screenshot the canvas at 1080 px on the short side, and pipe into ffmpeg (libx264, yuv420p, crf 18) to make motion.mp4. Close the browser at the end. Accept an optional JSON file argument that overrides CONFIG.

[Check before finishing]
Render one still per beat into a contact sheet and compare the frame at time 0 with the frame at the full duration pixel by pixel — they must match. Check that each poem line is readable on its sky, the windows light one by one at night, and nothing is clipped. Fix and re-render if anything fails. Finish with the file paths and the single command to re-render after editing settings.

[Final output format]
Output size 1080x1920 pixels, 9:16 portrait story. Keep all text inside the central 80% of the height: compress every zone percentage below into the 10-90% range.
This selected output format takes priority over any fixed canvas size or aspect ratio elsewhere in this template. Adapt the composition, text zones and margins to the selected canvas without stretching or cropping essential content. Device safe areas apply only when a device is selected. Never print these format instructions on the image.