docs(control-plane): explain state machines as interpretation tables (#2923)

Author: huangruiteng

docs/product/core-control-plane/README.md

@@ -31,6 +31,18 @@ rediscovering state from chat history or private planning notes. The rule seam
 map is intentionally behavior-preserving: it names extraction seams and parity
 checks before the refactor branch moves control-plane code.
 
+The state machines in this folder are interpretation tables inside the
+harness's effect interpreter:
+
+```text
+effect request -> interpretation -> observation -> next effect
+```
+
+See the
+[Agent Loop Effect Interpreter RFC](../../architecture/rfcs/agent-loop-effect-interpreter-v0.md)
+and
+[Harness Is the Effectful Program](../../development/control-plane-course/01-agent-loop-effectful-program.md).
+
 ## Execution Ownership
 
 These graphs describe Kernel state and legal transitions. The surrounding turn