Add internal framework orchestration

docs/policy/architecture.md

@@ -34,9 +34,11 @@ The implemented internal components consist of:
 - `internal/artifact`, which resolves ordinary inline and unrestricted
   caller-selected file references;
 - `internal/validate`, which validates basic, JSON, and JSON Schema output
-  using filesystem and `fs.FS` schema sources; and
+  using filesystem and `fs.FS` schema sources;
 - `internal/llm`, which defines the provider-neutral generation boundary and
-  implements outbound OpenAI-compatible chat requests.
+  implements outbound OpenAI-compatible chat requests; and
+- `internal/usecase`, which coordinates preparation and execution across the
+  internal framework components.
 
 The defaults and renderer depend on the domain model. Prompt-definition and
 profile repositories use the domain model, file catalog, and YAML decoder. The
@@ -44,8 +46,9 @@ built-in profile repository supplies an embedded `fs.FS` to the profile
 package. Artifact reading uses the domain model and application-neutral
 defaults. Validation uses the domain model, file catalog, and JSON Schema
 implementation. The model client uses the domain model, application-neutral
-defaults, and an injected or standard-library HTTP client. Orchestration and
-the public engine have not yet been extracted.
+defaults, and an injected or standard-library HTTP client. The use-case runner
+depends on the narrow interfaces owned by each internal component. The public
+engine has not yet been extracted.
 
 Future framework extraction must follow this dependency direction: