Add selective clean function for build directory

cmake/CleanBuild.cmake

@@ -0,0 +1,57 @@
+# cmake/CleanBuild.cmake
+
+# Function to selectively clean the build directory.
+#
+# This function will remove most of the generated build files from the build
+# directory, while preserving specific directories that contain downloaded
+# tools or generated documentation.
+#
+# Golden Rules:
+# - never delete build/
+# - never delete build/bin
+# - never delete build/docs
+# - never delete build/sdk (non cache)
+#
+# It will:
+# - purge build files
+# - clean up conan build files, cached sources can always remain.
+function(selective_clean_build_dir)
+    if(EXISTS "${CMAKE_SOURCE_DIR}/build")
+        message(STATUS "Selectively cleaning build directory: ${CMAKE_SOURCE_DIR}/build")
+
+        # List of top-level items in the build directory to keep.
+        set(golden_items
+            "${CMAKE_SOURCE_DIR}/build/bin"
+            "${CMAKE_SOURCE_DIR}/build/docs"
+            "${CMAKE_SOURCE_DIR}/build/sdk"
+        )
+
+        # Get all top-level items in the build directory.
+        file(GLOB top_level_items "${CMAKE_SOURCE_DIR}/build/*")
+
+        foreach(item ${top_level_items})
+            list(FIND golden_items "${item}" is_golden)
+            if(is_golden STREQUAL "-1")
+                string(FIND "${item}" "${CMAKE_SOURCE_DIR}/build" is_prefixed)
+                if(is_prefixed EQUAL 0)
+                    message(STATUS "Removing: ${item}")
+                    if(IS_DIRECTORY ${item})
+                        file(REMOVE_RECURSE "${item}")
+                    else()
+                        file(REMOVE "${item}")
+                    endif()
+                else()
+                    message(WARNING "Safety check failed: Will not remove '${item}' because it is not prefixed with CMAKE_SOURCE_DIR/build.")
+                endif()
+            else()
+                message(STATUS "Keeping golden item: ${item}")
+            endif()
+        endforeach()
+
+        message(STATUS "Selective clean complete.")
+    else()
+        message(STATUS "Build directory not found, skipping clean.")
+    endif()
+endfunction()
+
+selective_clean_build_dir()