Make consumer documentation easier to follow

docs/internal/overview.md

@@ -179,3 +179,9 @@ reflection behavior by `schema_test.go`, `projection_test.go`, and
 `decode_test.go`. The [development test map](../development.md#task-to-test-map)
 links focused commands. [`clone.go`](../../internal/engine/clone.go) owns typed
 copying, using the shared descriptors and per-operation traversal helpers.
+
+Each schema operation builds its private reflection descriptor graph with
+operation-local caching; there is no global mutable descriptor cache. Decoding,
+projection, and cloning reuse these descriptors so field bindings agree. The
+public reference describes the resulting type, output, and ownership behavior;
+this descriptor storage is an implementation detail.