nested state path

src/wf_authoring/ops/values.py

@@ -141,7 +141,11 @@ def pick_path(input: PickPathInput) -> ValueOutput:
 def project_fields(input: ProjectFieldsInput) -> MappingOutput:
     """Return only the requested existing fields from a mapping."""
     return MappingOutput(
-        mapping={field: input.mapping[field] for field in input.fields if field in input.mapping}
+        mapping={
+            field: input.mapping[field]
+            for field in input.fields
+            if field in input.mapping
+        }
     )
 
 

src/wf_core/models/schemas.py

@@ -17,7 +17,7 @@ class SchemaRef(BaseModel):
 
 
 class StateField(BaseModel):
-    """Declared root state field plus its runtime merge behavior."""
+    """Declared state path plus its runtime merge behavior."""
 
     type: str
     merge_strategy: Literal["replace", "append", "merge_object"] = "replace"
@@ -26,7 +26,7 @@ class StateField(BaseModel):
 
 
 class StateSchema(BaseModel):
-    """Workflow state schema keyed by declared root field name."""
+    """Workflow state schema keyed by declared exact state path."""
 
     model_config = ConfigDict(extra="allow")
 

src/wf_core/runtime/ops/merges.py

@@ -23,15 +23,23 @@ def apply_builtin_merge(
 
     if strategy == "append":
         if current_value is None:
-            return [incoming_value] if not isinstance(incoming_value, list) else incoming_value
+            return (
+                [incoming_value]
+                if not isinstance(incoming_value, list)
+                else incoming_value
+            )
         if not isinstance(current_value, list):
             raise WorkflowExecutionError(
                 f"cannot append into non-list state path {destination_path!r}"
             )
-        return [
-            *current_value,
-            *incoming_value,
-        ] if isinstance(incoming_value, list) else [*current_value, incoming_value]
+        return (
+            [
+                *current_value,
+                *incoming_value,
+            ]
+            if isinstance(incoming_value, list)
+            else [*current_value, incoming_value]
+        )
 
     if strategy == "merge_object":
         if current_value is None:

src/wf_core/runtime/ops/state.py

@@ -39,7 +39,9 @@ def apply_mapped_state(
     missing_field_message: str,
 ) -> dict[str, Any]:
     if has_overlapping_paths(mapping.values()):
-        raise WorkflowExecutionError("mapped state patch has overlapping destination paths")
+        raise WorkflowExecutionError(
+            "mapped state patch has overlapping destination paths"
+        )
 
     patch: dict[str, Any] = {}
     for source_field, destination_path in mapping.items():
@@ -69,8 +71,8 @@ def write_state_value(
             f"executor only supports writes into state.*, got {destination_path!r}"
         )
 
-    field_name = parts[0]
-    declared_field = workflow.state_schema.fields.get(field_name)
+    declared_path = ".".join(parts)
+    declared_field = workflow.state_schema.fields.get(declared_path)
     merge_strategy = declared_field.merge_strategy if declared_field else "replace"
     key_path = parts
     current_value = get_nested_value(state, key_path)