reducer as wf_mcp capability

tests/artifacts/test_factory.py

@@ -33,6 +33,26 @@ def test_create_workflow_artifact_from_plan_derives_boundary_schemas() -> None:
     assert artifact.created_from_catalog_version == "catalog-1"
 
 
+def test_create_workflow_artifact_from_plan_adds_reducer_dependencies() -> None:
+    plan = _plan()
+    plan["state_schema"] = {
+        "fields": {"best_score": {"type": "integer", "reducer": "wf.std.max"}}
+    }
+
+    artifact = create_workflow_artifact_from_plan(
+        artifact_id="score",
+        version=1,
+        title="Score",
+        plan=plan,
+        outcomes=("done",),
+    )
+
+    reducer = artifact.required_capabilities["wf.std.max"]
+    assert reducer.logical_source == "wf.std"
+    assert reducer.capability_name == "max"
+    assert reducer.kind == "reducer"
+
+
 def test_create_workflow_artifact_from_plan_accepts_wrapper_kind() -> None:
     artifact = create_workflow_artifact_from_plan(
         artifact_id="normalize_status",

tests/artifacts/test_validation.py

@@ -176,3 +176,28 @@ def test_validate_deployment_allows_changed_schema_when_policy_allows() -> None:
     )
 
     assert diagnostics == []
+
+
+def test_validate_deployment_accepts_reducer_capability() -> None:
+    reducer = RequiredCapability(
+        logical_source="wf.std",
+        capability_name="set_union",
+        kind="reducer",
+    )
+    diagnostics = validate_deployment_dependencies(
+        artifact=artifact_with(reducer),
+        deployment=deployment(bindings={"wf.std": "wf.std"}),
+        sources=[
+            AvailableSource(
+                id="wf.std",
+                capabilities={
+                    "set_union": AvailableCapability(
+                        name="set_union",
+                        kind="reducer",
+                    )
+                },
+            )
+        ],
+    )
+
+    assert diagnostics == []