reducer replaces merge_strategy.

tests/authoring/helpers.py

@@ -41,7 +41,7 @@ class AutoBindState(BaseModel):
 
 
 class AppendState(BaseModel):
-    items: Annotated[list[str], state_field(merge_strategy="append")] = Field(
+    items: Annotated[list[str], state_field(reducer="wf.std.append")] = Field(
         default_factory=list
     )
 
@@ -54,7 +54,7 @@ class DefaultedState(BaseModel):
 
 class NestedPersonState(BaseModel):
     name: str
-    tags: Annotated[list[str], state_field(merge_strategy="append")] = Field(
+    tags: Annotated[list[str], state_field(reducer="wf.std.append")] = Field(
         default_factory=list
     )
 

tests/authoring/test_schemas.py

@@ -46,7 +46,7 @@ def test_builder_accepts_typeddict_for_json_schema_refs() -> None:
     assert workflow.input_schema.properties["text"]["type"] == "string"
 
 
-def test_state_basemodel_can_declare_merge_strategy_with_annotated_metadata() -> None:
+def test_state_basemodel_can_declare_reducer_with_annotated_metadata() -> None:
     builder = WorkflowBuilder(
         name="state_metadata_demo",
         input_schema=WorkflowInput,
@@ -58,7 +58,7 @@ def test_state_basemodel_can_declare_merge_strategy_with_annotated_metadata() ->
     workflow = builder.compile()
 
     assert workflow.state_schema.fields["items"].type == "array"
-    assert workflow.state_schema.fields["items"].merge_strategy == "append"
+    assert workflow.state_schema.fields["items"].reducer == "wf.std.append"
 
 
 def test_state_basemodel_seeds_safe_initial_defaults() -> None:
@@ -96,5 +96,5 @@ def test_nested_state_basemodel_projects_parent_and_child_paths() -> None:
     assert workflow.state_schema.fields["person"].type == "object"
     assert workflow.state_schema.fields["person.name"].type == "string"
     assert workflow.state_schema.fields["person.tags"].type == "array"
-    assert workflow.state_schema.fields["person"].merge_strategy == "replace"
-    assert workflow.state_schema.fields["person.tags"].merge_strategy == "append"
+    assert workflow.state_schema.fields["person"].reducer == "wf.std.replace"
+    assert workflow.state_schema.fields["person.tags"].reducer == "wf.std.append"

tests/core/test_nested_state_paths.py

@@ -4,9 +4,9 @@ from wf_core import SchemaRef, StateField, StateSchema, Workflow
 from wf_core.runtime.ops.state import write_state_value
 
 
-def test_exact_nested_state_path_uses_declared_merge_strategy() -> None:
+def test_exact_nested_state_path_uses_declared_reducer() -> None:
     workflow = _workflow(
-        fields={"person.tags": StateField(type="array", merge_strategy="append")}
+        fields={"person.tags": StateField(type="array", reducer="wf.std.append")}
     )
     state = {"person": {"tags": ["seed"]}}
 
@@ -17,7 +17,7 @@ def test_exact_nested_state_path_uses_declared_merge_strategy() -> None:
 
 def test_parent_state_declaration_does_not_apply_to_nested_write() -> None:
     workflow = _workflow(
-        fields={"person": StateField(type="object", merge_strategy="merge_object")}
+        fields={"person": StateField(type="object", reducer="wf.std.merge_object")}
     )
     state = {"person": {"tags": ["seed"]}}
 
@@ -35,6 +35,22 @@ def test_undeclared_nested_state_path_defaults_to_replace() -> None:
     assert state["person"]["tags"] == ["next"]
 
 
+def test_state_field_defaults_to_replace_reducer() -> None:
+    assert StateField(type="string").reducer == "wf.std.replace"
+
+
+def test_unknown_state_reducer_fails_clearly() -> None:
+    workflow = _workflow(fields={"person.tags": StateField(type="array", reducer="x.nope")})
+    state = {"person": {"tags": ["seed"]}}
+
+    try:
+        write_state_value(workflow, state, "state.person.tags", ["next"])
+    except Exception as exc:
+        assert "unknown reducer 'x.nope'" in str(exc)
+    else:
+        raise AssertionError("expected unknown reducer to fail")
+
+
 def _workflow(*, fields: dict[str, StateField]) -> Workflow:
     return Workflow(
         name="nested_state_paths",

tests/rewrite/models.py

@@ -111,7 +111,7 @@ class UnsophisticatedPool(TypedDict):
 class Storage(BaseModel):
     "i NEED to do this?"
 
-    storage: Annotated[list[Entity], state_field(merge_strategy="append")] = Field(
+    storage: Annotated[list[Entity], state_field(reducer="wf.std.append")] = Field(
         default_factory=list
     )  # add!
 
@@ -125,7 +125,9 @@ class PartialRates(SophisticatedRates, total=False):
 
 
 class Rates(BaseModel):
-    rates: Annotated[PartialRates, state_field(merge_strategy="merge_object")]  # or_!
+    rates: Annotated[
+        PartialRates, state_field(reducer="wf.std.merge_object")
+    ]  # or_!
 
 
 class CurrentPools(BaseModel):