feat: compose stable product surfaces

docs/MODULE_ARCHITECTURE.md

@@ -1030,6 +1030,32 @@ Any future exception is extraction debt and must be temporary, documented in the
 script with a reason, and removed when a capability/API/event contract replaces
 it.
 
+## Product Surface Contributions
+
+`FrontendModule.product_surfaces` is the versioned product-composition contract
+for stable identities that may have one or more technical owners. A contribution
+declares contract version 1, a product identity, common label/icon/description,
+stable entry path, owner route and View surfaces, supported task/reader/admin/
+operator presentations, authorization requirements, capabilities, search
+sources, help contexts, documentation topics, migration aliases, and standard
+unavailable/degraded explanations.
+
+Core validates every reference against the owning manifest. Contributors that
+share an identity must agree on its common product metadata and entry path;
+entry and alias paths cannot belong to another product identity. The WebUI
+composes valid owners by product id, filters them through authorization and the
+effective View, and resolves the stable entry or migration alias to the first
+available owner route. It emits `govoplan:product-surface-route-resolved` before
+the redirect so migration telemetry can observe alias use without making the
+technical module part of the ordinary label.
+
+Use `ProductAvailabilityState` for unavailable and degraded outcomes. The
+ordinary state explains the attempted outcome, consequence, recovery path and
+responsible role. Exact module, capability, provider and correlation values may
+be supplied as a collapsed technical detail; they are not the primary error.
+The state is presentation only and never grants authority or changes provider
+health.
+
 ## Boundary Decision Register
 
 These durable decisions close older exploratory core issues. Implementation