feat: merge draft step maps

src/wf_mcp/workflow_surface/models.py

@@ -206,21 +206,35 @@ class SetDraftRouteRequest(BaseModel):
 
 
 class SetStepInputMapRequest(BaseModel):
-    """Typed MCP request for replacing one step input map."""
+    """Typed MCP request for replacing or merging one step input map."""
 
     workspace_id: WorkspaceId
     revision: int = Field(ge=1, description="Expected current workspace revision.")
     step_id: str = Field(description="Draft step id whose input map should change.")
     input_map: DraftPathMap
+    merge: bool = Field(
+        default=False,
+        description=(
+            "When false, replace the full input map. When true, preserve existing "
+            "bindings and add/update only input_map entries."
+        ),
+    )
 
 
 class SetStepOutputMapRequest(BaseModel):
-    """Typed MCP request for replacing one step output map."""
+    """Typed MCP request for replacing or merging one step output map."""
 
     workspace_id: WorkspaceId
     revision: int = Field(ge=1, description="Expected current workspace revision.")
     step_id: str = Field(description="Draft step id whose output map should change.")
     output_map: DraftPathMap
+    merge: bool = Field(
+        default=False,
+        description=(
+            "When false, replace the full output map. When true, preserve existing "
+            "bindings and add/update only output_map entries."
+        ),
+    )
 
 
 class DeleteDraftWorkspaceRequest(BaseModel):

src/wf_mcp/workflow_surface/tools.py

@@ -399,7 +399,8 @@ def register_workflow_tools(server: FastMCP[Any], service: WfMcpService) -> None
         name="wf.workflow.set_step_input_map",
         title="Set Step Input Map",
         description=(
-            "Replace one compatibility step input map in a draft workspace. "
+            "Replace or merge one compatibility step input map in a draft workspace. "
+            "Set merge=true to preserve existing bindings while adding/updating entries. "
             "New one-capability bootstraps should prefer canonical input bindings."
         ),
     )
@@ -412,6 +413,7 @@ def register_workflow_tools(server: FastMCP[Any], service: WfMcpService) -> None
                 revision=request.revision,
                 step_id=request.step_id,
                 input_map=request.input_map,
+                merge=request.merge,
             )
         )
 
@@ -419,7 +421,8 @@ def register_workflow_tools(server: FastMCP[Any], service: WfMcpService) -> None
         name="wf.workflow.set_step_output_map",
         title="Set Step Output Map",
         description=(
-            "Replace one compatibility step output map in a draft workspace. "
+            "Replace or merge one compatibility step output map in a draft workspace. "
+            "Set merge=true to preserve existing bindings while adding/updating entries. "
             "New one-capability bootstraps should prefer canonical output bindings."
         ),
     )
@@ -432,6 +435,7 @@ def register_workflow_tools(server: FastMCP[Any], service: WfMcpService) -> None
                 revision=request.revision,
                 step_id=request.step_id,
                 output_map=request.output_map,
+                merge=request.merge,
             )
         )