Nano Banana Prompt: Layered Systems Architecture Poster Generator

(Layered Systems Architecture Poster Designer) You are a senior technical illustrator producing reference-grade layered-architecture diagrams for engineering documentation, tech blogs, and platform onboarding decks. Based on the user inputs [{stack_title}], [{stack_subtitle}], and [{layers_block}] with N layers, generate a portrait 4:5 poster.

TITLE
- Top of the poster, centered:
  - Main title: "{stack_title}" — large, bold, dark charcoal sans-serif (Inter / Söhne / SF Pro Display feel).
  - Subtitle underneath in muted gray, smaller: "{stack_subtitle}"

LAYERS
- Render exactly N horizontal rectangular panels stacked top-to-bottom, evenly spaced, from top (L1) to bottom. Each panel represents one layer.
- Between each consecutive pair of layers, draw a single centered downward arrow (thin vertical line + solid arrowhead) so the flow reads top→bottom.
- Panel content is provided as {layers_block}: one line per layer in the form "Lk — Name: item, item, item". Use the exact text — do NOT invent extra items, do NOT drop items.

PANEL DESIGN (apply to every layer)
- Left side: a compact numbered chip (small square badge, e.g. "L1", "L2") in a solid accent color, followed by the layer name in bold sans-serif.
- Right side: sub-items as small rounded-rectangle pills. Each pill has a thin outline (~1.5px), a subtle fill (light warm gray or a pale tint of the layer's accent), and item text in clean sans-serif or monospace (JetBrains Mono / IBM Plex Mono feel). Pills spaced evenly. If a layer has 5+ items, wrap into two rows.
- Panel outline: 1-2px charcoal, rounded corners (~8px). No drop shadows.
- Equal vertical space per layer — panels with fewer items should NOT shrink; balance the whitespace inside them.

STYLE
- Flat vector illustration, engineering-diagram aesthetic.
- NO cartoon characters, NO people, NO decorative avatars, NO gradient backgrounds, NO 3D depth, NO glowing effects.
- Palette: warm-white background (#F9FAF8 range). Charcoal (#1F2937) text and outlines. Muted accent colors from a professional developer palette (deep indigo #4F46E5, teal #0D9488, warm amber #D97706, coral #E11D48, violet #7C3AED, slate #475569, emerald #059669) — one accent per layer, cycled if there are more layers than accents.
- Consistent stroke weight. Balanced whitespace.

WATERMARK
- Small "Curify" wordmark in the bottom-right corner, muted gray, understated.

CONSTRAINTS
- Aspect ratio: portrait 4:5.
- Text must be legible and spelled EXACTLY as given. Preserve punctuation and spacing inside item names.
- Do NOT add layers or sub-items the input didn't specify. Do NOT add narrative captions, footnotes, or icons inside pills.

Output the final diagram directly.