fix: recurse validate into list, dict, and set parameters

Previously, validate() only checked direct Config values but skipped
Config objects nested inside collections, leaving required parameters
unchecked.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bpiwowar

src/experimaestro/core/objects/config.py

@@ -434,6 +434,20 @@ def postprocess(self, stub, config: Config, values):
 
         return TagFinder()(self.pyobject)
 
+    def _validate_value(self, value):
+        """Recursively validate a value, handling Config, list, dict, and set"""
+        if isinstance(value, Config):
+            value.__xpm__.validate()
+        elif isinstance(value, list):
+            for item in value:
+                self._validate_value(item)
+        elif isinstance(value, dict):
+            for item in value.values():
+                self._validate_value(item)
+        elif isinstance(value, set):
+            for item in value:
+                self._validate_value(item)
+
     def validate(self):
         """Validate a value"""
         if not self._validated:
@@ -443,8 +457,7 @@ def validate(self):
             for k, argument in self.xpmtype.arguments.items():
                 value = self.values.get(k)
                 if value is not None:
-                    if isinstance(value, Config):
-                        value.__xpm__.validate()
+                    self._validate_value(value)
                 elif argument.required:
                     if not argument.generator:
                         raise ValueError(

src/experimaestro/tests/test_validation.py

@@ -206,3 +206,34 @@ def test_validation_taskargument():
     with TemporaryExperiment("fake"):
         x.submit(run_mode=RunMode.DRY_RUN)
         expect_validate(TaskConfigConsumer.C(x=x))
+
+
+# --- Nested structures (list, dict, set)
+
+
+class ListConfig(Config):
+    items: Param[list[A]]
+
+
+class DictConfig(Config):
+    items: Param[dict[str, A]]
+
+
+def test_validation_list_valid():
+    """Validate recurses into list elements"""
+    expect_validate(ListConfig.C(items=[A.C(value=1), A.C(value=2)]))
+
+
+def test_validation_list_missing():
+    """Validate catches missing required params inside list elements"""
+    expect_notvalidate(ListConfig.C(items=[A.C(value=1), A.C()]))
+
+
+def test_validation_dict_valid():
+    """Validate recurses into dict values"""
+    expect_validate(DictConfig.C(items={"x": A.C(value=1), "y": A.C(value=2)}))
+
+
+def test_validation_dict_missing():
+    """Validate catches missing required params inside dict values"""
+    expect_notvalidate(DictConfig.C(items={"x": A.C(value=1), "y": A.C()}))