第6组：启用ccache加速重复编译并保持闭环

docs/linuxcnc-source-policy.md

@@ -57,6 +57,9 @@ Efficiency rules:
 - Default native, source-link, build-wasm, and wasm-safe CMake probe
   parallelism to `CNC_SIM_BUILD_JOBS:-8`; raise it only by explicit
   positive-integer environment override.
+- When `ccache` is available and `CXX` is unset, native and wasm build paths
+  should enable compiler caching automatically rather than requiring a manual
+  wrapper.
 - Persistent native, source-link, and wasm-safe CMake probe build directories
   may be overridden for local workflows, but must not point at the filesystem
   root.