Make tenancy an optional access integration

docs/ACCESS_MODULE_BOUNDARY.md

@@ -64,6 +64,27 @@ Access declares tenancy as an optional module integration. It uses the
 core-owned `core_scopes` table as the scope table, but it must not import
 `govoplan_tenancy` or require the tenancy package to start.
 
+## Core-Only Startup Contract
+
+A core-only installation must be able to start far enough to expose process
+health, module metadata, and the unauthenticated shell needed for installation
+or recovery work. It is not a usable authenticated product installation.
+
+Authenticated product use requires the `access` module or another module that
+provides the same kernel auth capabilities:
+
+- `auth.apiPrincipalProvider`
+- `auth.principalResolver`
+- `auth.permissionEvaluator`
+- `auth.tenantContextSwitcher`
+
+Access contributes the default implementations for those capabilities plus the
+interactive `/api/v1/auth/*` routes. Product modules should express auth needs
+as required capabilities or route permission requirements instead of importing
+access internals. Runtime configurations that intentionally omit access should
+hide authenticated navigation and return capability errors for authenticated
+product routes rather than failing process startup.
+
 ## Principal Context Contract
 
 The stable runtime principal is `govoplan_core.core.access.PrincipalRef`.