add the thing formally

src/wf_authoring/nodes/__init__.py

@@ -13,7 +13,7 @@ from .callables import (
 from .inference import accepts_context, infer_models, is_basemodel_subclass
 from .decorator import node
 from .registry import build_async_registry, build_registry
-from .result import NodeReturn
+from .result import NodeReturn, Nothing, outcome
 from .schema import schema_ref_for
 from .spec import NodeSpec
 
@@ -27,6 +27,7 @@ __all__ = [
     "NodeCallable",
     "NodeReturn",
     "NodeSpec",
+    "Nothing",
     "OutputT",
     "PlainNodeCallable",
     "SyncRegistryHandler",
@@ -36,5 +37,6 @@ __all__ = [
     "infer_models",
     "is_basemodel_subclass",
     "node",
+    "outcome",
     "schema_ref_for",
 ]

src/wf_authoring/nodes/result.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
-from typing import Generic, TypeVar
+from typing import Generic, TypeVar, overload
 
 from pydantic import BaseModel
 
@@ -14,3 +14,25 @@ class NodeReturn(Generic[OutputT_co]):
 
     outcome: str
     output: OutputT_co
+
+
+class Nothing(BaseModel):
+    """Empty output model for nodes that only choose an outcome."""
+
+
+@overload
+def outcome(name: str) -> NodeReturn[Nothing]: ...
+
+
+@overload
+def outcome(name: str, output: OutputT_co) -> NodeReturn[OutputT_co]: ...
+
+
+def outcome(
+    name: str,
+    output: OutputT_co | None = None,
+) -> NodeReturn[OutputT_co] | NodeReturn[Nothing]:
+    """Create a node result with an optional output model."""
+    if output is None:
+        return NodeReturn(outcome=name, output=Nothing())
+    return NodeReturn(outcome=name, output=output)