docs

docs/architecture/website/VIEW_DATA.md

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+# ViewData (Website Templates)
+
+ViewData is the **only** allowed input type for Templates in `apps/website`.
+
+## 1) Definition
+
+ViewData is a JSON-serializable, template-ready data structure:
+
+- primitives (strings/numbers/booleans)
+- arrays and plain objects
+- `null` for missing values
+
+## 2) What ViewData is NOT
+
+ViewData is not:
+
+- a Page DTO (raw transport)
+- a ViewModel (client-only class)
+- a Display Object instance
+
+## 3) Construction rules
+
+ViewData MUST be created in client code:
+
+1) Initial SSR-safe render: `ViewData = fromDTO(PageDTO)`
+2) Post-hydration render: `ViewData = fromViewModel(ViewModel)`
+
+Templates MUST NOT compute derived values.
+
+## 4) Determinism rules
+
+Any formatting used to produce ViewData MUST be deterministic.
+
+Forbidden anywhere in formatting code paths:
+
+- `Intl.*`
+- `Date.toLocaleString()` / `Date.toLocaleDateString()` / `Date.toLocaleTimeString()`
+
+Reason: SSR and browser outputs can differ.
+
+## 5) Relationship to Display Objects
+
+Display Objects are used to implement formatting/mapping, but their instances MUST NOT be stored inside ViewData.
+
+Only primitive outputs produced by Display Objects may appear in ViewData.
+