change

backend/engine/cdsl_engine/README.md

@@ -5,6 +5,20 @@ This package rebuilds `cad.cdsl.llm.v1` models through the CDSL-only path:
 `sketch_solver -> llm_compiler -> llm_engine -> STEP`
 
 Supported profiles are defined by `SHAPE_GENERATORS` in `sketch_solver.py`.
+Supported feature atomic operations are defined by the dispatch in `llm_engine.py`
+and their required parameters are defined by `REQUIRED` in `llm_compiler.py`.
+Their human-readable contract is in `profile_schema.json`; the complete,
+machine-enforced CDSL object contract is in `cdsl_schema.json`.
 The Studio only accepts self-contained profile data and requires successful
 `engine=cdsl_only` output. It never uses the legacy translator fallback or
 `compiler_context`.
+
+## Engine schema maintenance
+
+`profile_schema.json` and `cdsl_schema.json` together are the source of truth
+for the engine contract exposed to the CAD Agent and the backend validator.
+Any addition, removal, rename, or
+parameter-contract change in `sketch_solver.py`, `llm_compiler.py`, or
+`llm_engine.py` must update both files in the same change.
+`backend/tests/test_profile_schema.py` fails when the registered profiles or
+supported atomic operations diverge from the document.