feat: publish stable product surface composition

docs/architecture/PRODUCT_EXPERIENCE_AND_MODULE_BOUNDARIES.md

@@ -72,6 +72,23 @@ Each WebUI module should be able to announce:
 The contract references surfaces. It does not permit Core or a product package
 to import their implementation.
 
+The first versioned `product_surfaces` slice is now implemented in Core. It
+binds a stable product identity and entry path to one or more owner routes,
+View surfaces, presentations, capabilities, search sources, help contexts and
+documentation topics. It also carries standard unavailable/degraded
+explanations and migration aliases. Mail and Postbox contribute the first
+shared identity, `communication.messages`: `/messages` and the migration alias
+`/inbox` select the first currently authorized, View-visible owner while the
+underlying `/mail` and `/postbox` deep links, custody and permissions remain
+unchanged. Alias resolution emits a bounded client telemetry event before the
+redirect.
+
+Core's `ProductAvailabilityState` is the shared presentation primitive for
+authorization, Policy, configuration, disabled, missing-capability, offline and
+provider-degraded states. Product language is primary; exact module,
+capability, provider and correlation provenance is available only in an
+expandable technical section.
+
 ## Navigation Model
 
 The default shell should prioritize:
@@ -132,9 +149,9 @@ first rail slice.
 
 ### Slice 1: inventory and aliases
 
-- classify every route, navigation item, widget, setting, search object, and
+- continue classifying every route, navigation item, widget, setting, search object, and
   help context by product area and object type;
-- add product aliases without removing existing deep links;
+- extend the implemented product-surface aliases without removing existing deep links;
 - flag raw module IDs in ordinary-user labels and errors.
 
 ### Slice 2: work-first shell