Document main-relative companion loading

docs/policy/architecture.md

@@ -151,6 +151,11 @@ initialization, and resource checks. See the [configuration discovery
 contract](../config.md#configuration-discovery) and [ADR
 0019](../adr/0019-explicit-configuration-discovery.md).
 
+The layered loader may bind application-selected dependent locations after main
+selection. Applications still choose search conventions and must explicitly
+select an overlay. [ADR 0022](../adr/0022-main-relative-context.md) records
+the deferred context decision.
+
 The engine applies each input's mapping destination within the existing source
 assembly, applies immediate-parent-relative YAML destinations to imports, and
 retains each effective placement with source identity and inspection records;