Clarify in docs how runtime parameter resolution works

RELEASE.md

@@ -6,6 +6,7 @@
 ## Bug fixes and other changes
 * Moved `_find_run_command()` and `_find_run_command_in_plugins()` from `__main__.py` in the project template to the framework itself.
 * Fixed a bug where `%load_node` breaks with multi-lines import statements.
+* Fixed runtime parameters resolution in `OmegaConfigLoader` by only loading them once.
 
 ## Breaking changes to the API
 

kedro/config/omegaconf_config.py

@@ -343,7 +343,9 @@ def load_and_merge_dir_config(  # noqa: PLR0913
         if not aggregate_config:
             return {}
 
-        if key == "parameters":
+        # Only merge in runtime parameters once for the base env
+        is_base_env = conf_path.endswith(self.base_env)
+        if key == "parameters" and is_base_env:
             # Merge with runtime parameters only for "parameters"
             return OmegaConf.to_container(
                 OmegaConf.merge(*aggregate_config, self.runtime_params), resolve=True

tests/config/test_omegaconf_config.py

@@ -1068,6 +1068,45 @@ def test_runtime_params_resolution(self, tmp_path):
         # runtime params are resolved correctly in catalog
         assert conf["catalog"]["companies"]["type"] == runtime_params["dataset"]["type"]
 
+    def test_runtime_params_resolution_with_env(self, tmp_path):
+        base_params = tmp_path / _BASE_ENV / "parameters.yml"
+        prod_params = tmp_path / "prod" / "parameters.yml"
+        runtime_params = {
+            "aaa": {
+                "bbb": {
+                    "abb": "2011-11-11",
+                }
+            }
+        }
+        param_config = {
+            "aaa": {
+                "bbb": {
+                    "aba": "2023-11-01",
+                    "abb": "2023-11-01",
+                    "abc": 14,
+                }
+            },
+            "xyz": {"asdf": 123123},
+        }
+        prod_param_config = {"def": {"gg": 123}}
+        _write_yaml(base_params, param_config)
+        _write_yaml(prod_params, prod_param_config)
+        conf = OmegaConfigLoader(
+            tmp_path,
+            base_env=_BASE_ENV,
+            default_run_env="prod",
+            runtime_params=runtime_params,
+        )
+
+        expected_parameters = {
+            "aaa": {"bbb": {"aba": "2023-11-01", "abb": "2011-11-11", "abc": 14}},
+            "xyz": {"asdf": 123123},
+            "def": {"gg": 123},
+        }
+
+        # runtime parameters are resolved correctly across parameter files from different environments
+        assert conf["parameters"] == expected_parameters
+
     def test_runtime_params_missing_default(self, tmp_path):
         base_params = tmp_path / _BASE_ENV / "parameters.yml"
         runtime_params = {