skill(data-viz): add lazy init, data-code separation, color contrast, icon semantics, field validation, pre-delivery checklist (#434)

Six improvements derived from session learnings — all general, none task-specific:

- component-guide: lazy chart initialization pattern for multi-tab dashboards
  (Chart.js/Recharts/Nivo all render blank in display:none containers)
- component-guide: data-code separation for programmatic HTML generation
  (f-string + JS curly braces cause silent parse failures)
- SKILL.md Design Principles: dynamic color safety rule for external/brand colors
- SKILL.md Design Principles: icon semantics check
- SKILL.md Anti-Patterns: warn against filtering on unvalidated data fields
- SKILL.md: pre-delivery checklist (tabs, fields, contrast, icons, tooltips, mobile)

Author: anandgupta42

.opencode/skills/data-viz/SKILL.md

@@ -100,6 +100,8 @@ A single insight might just be one chart with a headline and annotation. Scale c
 - **Responsive**: `min-h-[VALUE]` on all charts. Grid stacks on mobile
 - **Animation**: Entry transitions only, `duration-300` to `duration-500`. Never continuous
 - **Accessibility**: `aria-label` on charts, WCAG AA contrast, don't rely on color alone
+- **Dynamic color safety**: When colors come from external sources (brand palettes, category maps, API data, user config), never apply them directly as text color without a contrast check. Dark colors are invisible on dark card backgrounds. Safe pattern: use the external color only for non-text elements (left border, dot, underline); always use the standard text color (white / `var(--text)`) for the label itself. If color-coded text is required, apply a minimum lightness floor: `color: hsl(from brandColor h s max(l, 60%))`
+- **Icon semantics**: Verify every icon matches its label's actual meaning, not just its visual shape. Common traps: using a rising-trend icon (📈) for metrics where lower is better (latency, error rate, cost); using achievement icons (🏆) for plain counts. When in doubt, use a neutral descriptive icon over a thematic one that could mislead
 
 ### Step 5: Interactivity & Annotations
 
@@ -133,3 +135,16 @@ A single insight might just be one chart with a headline and annotation. Scale c
 - Pie charts > 5 slices — use horizontal bar
 - Unlabeled dual y-axes — use two separate charts
 - Truncated bar axes — always start at zero
+- Filtering or mapping over a field not confirmed to exist in the data export — an undefined field in `.filter()` or `.map()` produces empty arrays or NaN silently, not an error; always validate the exported schema matches what the chart code consumes
+
+## Pre-Delivery Checklist
+
+Before marking a dashboard complete:
+
+- [ ] Every tab / view activated — all charts render (no blank canvases, no unexpected 0–1 axes)
+- [ ] Every field referenced in chart/filter code confirmed present in the data export
+- [ ] All text readable on its background — check explicitly when colors come from external data
+- [ ] All icons match their label's meaning
+- [ ] Tooltips appear on hover for every chart
+- [ ] No chart silently receives an empty dataset — add a visible empty state or console warning
+- [ ] Mobile: grid stacks correctly, no body-level horizontal overflow

.opencode/skills/data-viz/references/component-guide.md

@@ -392,3 +392,70 @@ const CalloutLabel = ({ viewBox, label, color = "#1e293b" }: { viewBox?: { x: nu
 ```
 
 **Rules:** Never overlap data. Use `position: "insideTopRight"/"insideTopLeft"` on labels. Pair annotations with tooltips — annotation names the event, tooltip shows the value.
+
+---
+
+## Multi-Tab Dashboard — Lazy Chart Initialization
+
+Charts initialized inside a hidden container (`display:none`) render blank. Chart.js, Recharts, and Nivo all read container dimensions at mount time — a hidden container measures as `0×0`.
+
+**Rule: never initialize a chart until its container is visible.**
+
+```js
+// Vanilla JS pattern
+var _inited = {};
+
+function activateTab(name) {
+  // 1. make the tab visible first
+  document.querySelectorAll('.tab').forEach(el => el.classList.remove('active'));
+  document.getElementById('tab-' + name).classList.add('active');
+  // 2. then initialize charts — only on first visit
+  if (!_inited[name]) {
+    _inited[name] = true;
+    initChartsFor(name);
+  }
+}
+
+activateTab('overview'); // init the default visible tab on page load
+```
+
+Library-specific notes:
+- **Chart.js**: canvas reads as `0×0` inside `display:none` — bars/lines never appear
+- **Recharts `ResponsiveContainer`**: reads `clientWidth = 0` — chart collapses to nothing
+- **Nivo `Responsive*`**: uses `ResizeObserver` — fires once at `0×0`, never re-fires on show
+- **React conditional rendering**: prefer `visibility:hidden` + `position:absolute` over toggling `display:none` if you want charts to stay mounted and pre-rendered
+
+---
+
+## Programmatic Dashboard Generation — Data-Code Separation
+
+When generating a standalone HTML dashboard from a script (Python, shell, etc.), never embed JSON data inside a template string that also contains JavaScript. Curly-brace collisions in f-strings / template literals cause silent JS parse failures that are hard to debug.
+
+**Wrong** — data and JS logic share one f-string, every `{` in JS must be escaped as `{{`:
+
+```python
+html = f"""
+<script>
+  const data = {json.dumps(data)};          // fine
+  const fn = () => {{ return x; }}           // must escape — easy to miss
+  const obj = {{ key: getValue() }};         // one missed escape = blank page
+</script>
+"""
+```
+
+**Right** — separate data from logic entirely:
+
+```python
+# Step 1: write data to its own file — no template string needed
+with open('data.js', 'w') as f:
+    f.write('const DATA = ' + json.dumps(data) + ';')
+
+# Step 2: HTML loads both files; app.js is static and never needs escaping
+```
+
+```html
+<script src="data.js"></script>   <!-- generated, data only -->
+<script src="app.js"></script>    <!-- static, logic only   -->
+```
+
+Benefits: `app.js` is static and independently testable; `data.js` is regenerated without touching logic; no escaping required in either file.