chore: enforce shared WebUI layouts

docs/architecture/INTERFACE_PATTERN_LANGUAGE.md

@@ -51,6 +51,55 @@ rules:
 - Preserve a stable way back to the containing object and the broader system.
 - Do not let navigation, selection, or a view switch imply consent.
 
+## Shared Component And Layout Architecture
+
+Core owns the reusable WebUI vocabulary; modules own domain composition and
+behavior. Centralization follows four layers:
+
+| Layer | Owner | Examples | Rule |
+| --- | --- | --- | --- |
+| Foundation | Core | theme tokens, spacing, typography, focus and responsive breakpoints | Modules consume the contract and do not redefine it. |
+| Primitives | Core | buttons, fields, dialogs, alerts, cards, tables, loading, empty and blocked states | A matching primitive is reused rather than copied locally. |
+| Structural layouts | Core | page frame and header, action region, workspace panes, toolbars, grids, form sections and dialog anatomy | Layout owns geometry, scroll, responsive collapse and accessibility, but no domain decisions. |
+| Domain compositions | Owning module | a campaign review, mailbox, records explorer or operations dashboard | Modules select shared pieces, bind data and permissions, and retain domain wording and consequences. |
+
+A component belongs in Core when it is used or expected in more than one
+module and central ownership materially protects accessibility, responsive
+behavior, localization, contextual help, theming, or interaction consistency.
+A component stays module-owned when its API would otherwise encode a domain
+entity, permission, workflow state, endpoint, or policy decision. Reuse does
+not justify moving domain semantics into Core.
+
+`PageLayout` is the standard frame for headed workflow, dashboard,
+configuration, monitoring and explanatory pages. It owns the scroll viewport,
+content inset, sticky responsive header, title and description geometry,
+route-action placement, transient page notices, loading boundary and page help
+identity. `PageHeader` is the escape hatch for full-canvas archetypes that need
+the same header contract but must own their workspace scroll. Specialized
+layouts such as `AdminPageLayout` compose these lower-level Core contracts;
+they do not repeat their markup or responsive CSS.
+
+Module CSS may arrange domain content inside a shared layout. It must not
+override Core layout internals or copy the outer page, dialog, toolbar, form or
+state skeleton under a module-prefixed name. If an archetype cannot be
+expressed by the central API, extend the central contract or record a bounded
+exception before introducing local structure.
+
+Migration is incremental and enforceable:
+
+1. inventory copied structures and register existing debt;
+2. introduce the smallest domain-neutral Core contract with accessibility,
+   help, localization, theme and narrow-layout tests;
+3. migrate representative Core and optional-module consumers;
+4. reject new copies while removing registered debt in bounded module batches;
+5. promote the next repeated structure only after its variants and extension
+   points are understood.
+
+The intended next structural contracts are workspace/split-pane layout,
+responsive page toolbar, content grid, form-section layout, dialog body/footer
+layout and shared empty/error state composition. Their APIs must remain
+composable; a central component is not a single oversized page template.
+
 ## Surface Archetypes
 
 Choose an archetype from the task, then specialize it for the domain. A route
@@ -101,7 +150,8 @@ one.
   creation panel.
 - Workflow, configuration, dashboard, and explanatory pages may use a heading.
   The heading names the task or scoped object and contains only route-level
-  actions.
+  actions. Use the Core `PageLayout` contract for the frame and `PageHeader`
+  only when a full-canvas archetype owns its own scrolling.
 - Put a collection-wide create action in the heading of the collection it
   affects. Use a short, specific label such as `Add` when the heading already
   names the object. Do not duplicate that action in a permanently visible side