feat: add draft state schema projection helper

src/wf_mcp/workflow_surface/models.py

@@ -237,6 +237,20 @@ class SetStepOutputMapRequest(BaseModel):
     )
 
 
+class AddStateFromOutputRequest(BaseModel):
+    """Typed MCP request for declaring a state field from a step output schema."""
+
+    workspace_id: WorkspaceId
+    revision: int = Field(ge=1, description="Expected current workspace revision.")
+    step_id: str = Field(description="Draft step id whose capability output is used.")
+    output_field: str = Field(
+        description="Top-level output field to copy, for example after."
+    )
+    state_path: str = Field(
+        description="Root state path to declare, for example state.after."
+    )
+
+
 class DeleteDraftWorkspaceRequest(BaseModel):
     """Typed MCP request payload for deleting one draft workspace."""
 

src/wf_mcp/workflow_surface/tools.py

@@ -12,6 +12,7 @@ from wf_mcp.broker.service import WfMcpService
 from wf_mcp.broker.service.workflow_operation_context import context_from_service
 
 from .models import (
+    AddStateFromOutputRequest,
     CallCapabilityResult,
     CreateArtifactFromWorkspaceRequest,
     CreateDraftWorkspaceFromCapabilityRequest,
@@ -439,6 +440,27 @@ def register_workflow_tools(server: FastMCP[Any], service: WfMcpService) -> None
             )
         )
 
+    @server.tool(
+        name="wf.workflow.add_state_from_output",
+        title="Add State From Output",
+        description=(
+            "Declare one root state field by copying a draft step capability output "
+            "field schema, including local $defs/definitions when present."
+        ),
+    )
+    async def add_state_from_output(
+        request: AddStateFromOutputRequest,
+    ) -> DraftWorkspaceResult:
+        return DraftWorkspaceResult.model_validate(
+            await handlers.add_state_schema_from_output(
+                workspace_id=request.workspace_id,
+                revision=request.revision,
+                step_id=request.step_id,
+                output_field=request.output_field,
+                state_path=request.state_path,
+            )
+        )
+
     @server.tool(
         name="wf.workflow.create_minimal_draft_workspace",
         title="Create Minimal Draft Workspace",