Fail fast on unknown collection_type instead of silent fallbacks.

- collection_runtime_discriminator: raise ValueError for unknown types
- _runtime_model_for_collection_type: remove nested-type fallback to generic models
- py_type_internal_json: raise on unrecognized declared collection_type
- _validate_collection_runtime_dict: raise instead of trying list/generic models
- Add tests for discriminator routing, unknown type rejection

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jmchilton

lib/galaxy/tool_util_models/parameters.py

@@ -831,9 +831,13 @@ def collection_runtime_discriminator(v: Any) -> str:
             return "nested_list"
         else:
             return "nested_record"
-    else:
-        # Unknown type - default to list (matches historical behavior)
+    elif not ct:
+        # Missing collection_type — data isn't a runtime collection dict.
+        # Route to list so Pydantic fails validation with a clear schema error
+        # rather than a discriminator error.
         return "list"
+    else:
+        raise ValueError(f"Unknown collection_type for runtime discrimination: '{ct}'")
 
 
 CollectionRuntimeDiscriminated: Type = cast(
@@ -1129,13 +1133,6 @@ def _runtime_model_for_collection_type(self, ct: str) -> tuple:
         model = build_collection_model_for_type(ct)
         if model is not None:
             return (model, ct)
-        if ":" in ct:
-            # Fallback to generic nested models for unknown nested types
-            first_segment = ct.split(":")[0]
-            if first_segment in ("list", "sample_sheet"):
-                return (DataCollectionNestedListRuntime, "nested_list")
-            else:
-                return (DataCollectionNestedRecordRuntime, "nested_record")
         return (None, None)
 
     @property
@@ -1176,8 +1173,7 @@ def py_type_internal_json(self) -> Type:
         if model:
             return optional_if_needed(model, self.optional)
 
-        # Fallback for unrecognized types - use full discriminated union
-        return optional_if_needed(CollectionRuntimeDiscriminated, self.optional)
+        raise ValueError(f"Unknown collection_type for runtime model: '{self.collection_type}'")
 
     def pydantic_template(self, state_representation: StateRepresentationT) -> DynamicModelInformation:
         if state_representation in ["request", "relaxed_request"]:

lib/galaxy/tools/runtime.py

@@ -17,9 +17,6 @@
 from galaxy.tool_util_models.parameters import (
     build_collection_model_for_type,
     DataCollectionInternalJsonBase,
-    DataCollectionListRuntime,
-    DataCollectionNestedListRuntime,
-    DataCollectionNestedRecordRuntime,
     DataCollectionRequestInternal,
     DataInternalJson,
     DataRequestInternalDereferencedT,
@@ -185,15 +182,7 @@ def _validate_collection_runtime_dict(raw: dict[str, Any]) -> DataCollectionInte
     model = build_collection_model_for_type(ct)
     if model is not None:
         return model.model_validate(raw)
-    # Fallback for unknown types
-    if ":" in ct:
-        first_segment = ct.split(":")[0]
-        if first_segment in ("list", "sample_sheet"):
-            return DataCollectionNestedListRuntime.model_validate(raw)
-        else:
-            return DataCollectionNestedRecordRuntime.model_validate(raw)
-    # Unknown single type - try list (historical behavior)
-    return DataCollectionListRuntime.model_validate(raw)
+    raise ValueError(f"Cannot build runtime model for collection_type: '{ct}'")
 
 
 def _build_collection_runtime_dict(

test/unit/app/tools/test_runtime.py

@@ -15,7 +15,10 @@
     DataCollectionSampleSheetRuntime,
     DataInternalJson,
 )
-from galaxy.tools.runtime import collection_to_runtime
+from galaxy.tools.runtime import (
+    _validate_collection_runtime_dict,
+    collection_to_runtime,
+)
 
 
 @pytest.fixture
@@ -226,3 +229,17 @@ def test_collection_to_runtime_deeply_nested(mock_adapt_dataset):
     inner = middle.elements[0]
     assert isinstance(inner, DataCollectionPairedRuntime)
     assert inner.elements.forward.class_ == "File"
+
+
+def test_validate_collection_runtime_dict_rejects_unknown_leaf():
+    """Unknown leaf collection_type raises ValueError."""
+    raw = {"class": "Collection", "name": "x", "collection_type": "banana", "tags": [], "elements": []}
+    with pytest.raises(ValueError, match="Cannot build runtime model"):
+        _validate_collection_runtime_dict(raw)
+
+
+def test_validate_collection_runtime_dict_rejects_unknown_nested():
+    """Unknown nested collection_type raises ValueError."""
+    raw = {"class": "Collection", "name": "x", "collection_type": "list:banana", "tags": [], "elements": []}
+    with pytest.raises(ValueError, match="Cannot build runtime model"):
+        _validate_collection_runtime_dict(raw)

test/unit/tool_util/test_runtime.py

@@ -3,6 +3,7 @@
 
 from galaxy.tool_util_models.parameters import (
     build_collection_model_for_type,
+    collection_runtime_discriminator,
     DataCollectionListRuntime,
     DataCollectionPairedRuntime,
     DataCollectionRecordRuntime,
@@ -249,3 +250,26 @@ def test_dynamic_model_json_schema_deeply_nested():
     defs = schema.get("$defs", {})
     assert len(defs) >= 2
     assert any("list_paired" in k for k in defs.keys())
+
+
+def test_collection_runtime_discriminator_known_types():
+    """Known leaf and nested types route correctly."""
+    assert collection_runtime_discriminator({"collection_type": "list"}) == "list"
+    assert collection_runtime_discriminator({"collection_type": "paired"}) == "paired"
+    assert collection_runtime_discriminator({"collection_type": "record"}) == "record"
+    assert collection_runtime_discriminator({"collection_type": "paired_or_unpaired"}) == "paired_or_unpaired"
+    assert collection_runtime_discriminator({"collection_type": "sample_sheet"}) == "sample_sheet"
+    assert collection_runtime_discriminator({"collection_type": "list:paired"}) == "nested_list"
+    assert collection_runtime_discriminator({"collection_type": "record:paired"}) == "nested_record"
+
+
+def test_collection_runtime_discriminator_rejects_unknown():
+    """Unknown collection_type raises ValueError instead of silently defaulting."""
+    with pytest.raises(ValueError, match="Unknown collection_type"):
+        collection_runtime_discriminator({"collection_type": "banana"})
+
+
+def test_collection_runtime_discriminator_missing_routes_to_list():
+    """Missing/empty collection_type routes to list for Pydantic schema rejection."""
+    assert collection_runtime_discriminator({"collection_type": ""}) == "list"
+    assert collection_runtime_discriminator({}) == "list"