Initial release: diagram-design v1.0

Thirteen editorial diagram types (architecture, flowchart, sequence,
state, ER, timeline, swimlane, quadrant, nested, tree, layers, venn,
pyramid) as self-contained HTML files with inline SVG.

Progressive disclosure: lean SKILL.md points to per-type references.
Neutral stone+rust default skin, first-run gate that prompts users
to customize the style guide from their own website, URL-based
onboarding, annotation-callout primitive, sketchy filter variant,
live gallery at assets/index.html.

references/type-layers.md

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+# Layer Stack
+
+**Best for:** OSI model, CSS cascade, context hierarchy, tech stack, abstraction layers, memory hierarchy.
+
+## Layout conventions
+- Horizontal bands stacked vertically. Each layer is a full-width rectangle (same x, same width). 4–6 layers total.
+- Layer height 56–72px, width typically 800–880px inside a 1000px viewBox.
+- Each row contains (left→right):
+  1. **Index tag** on the far left (`L3`, `07`, `APPLICATION`) — Geist Mono 8–9px eyebrow.
+  2. **Layer name** slightly right of center-left — Geist 14–16px 600.
+  3. **Sublabel / note** on the far right — Geist Mono 9–10px muted.
+- Border between layers: 1px hairline `rgba(11,13,11,0.12)`. Outer silhouette 1px ink or muted.
+- Fills: either alternating subtle shades (paper / paper-2) OR all paper with hairline dividers. Pick one and hold it.
+- Direction indicator on the LEFT margin (outside the stack): small up/down arrow + Geist Mono label (`abstraction ↑`, `packets ↓`).
+- Coral on **one** focal layer (stroke + subtle tint fill) — the bottleneck, the pay-rent layer, the one under discussion.
+
+## Anti-patterns
+- Layers that aren't actually hierarchical (use swimlane or architecture).
+- Skipped numbering (missing L4 between L3 and L5 without explanation).
+- Every layer a different color — hierarchy invisible.
+- Inconsistent layer heights without reason.
+
+## Examples
+- `assets/example-layers.html` — minimal light
+- `assets/example-layers-dark.html` — minimal dark
+- `assets/example-layers-full.html` — full editorial