move subgraph operations to wf_api

ok these are some composition stuff so tgis is probably the right place to live

tests/wf_api/test_saved_subgraphs_extraction.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+import wf_api.saved_subgraphs as canonical
+import wf_mcp.workflow_surface.saved_subgraphs as shim
+
+
+def test_canonical_import_exports_expected_symbols() -> None:
+    assert hasattr(canonical, "SavedSubgraphTree")
+    assert hasattr(canonical, "resolve_saved_subgraph_tree")
+    assert hasattr(canonical, "prepare_saved_subgraphs")
+    assert hasattr(canonical, "validate_saved_subgraph_tree")
+    assert hasattr(canonical, "saved_subgraph_tree_from_snapshots")
+    assert hasattr(canonical, "direct_wrapper_interrupt_diagnostic")
+
+
+def test_shim_import_still_works() -> None:
+    assert hasattr(shim, "SavedSubgraphTree")
+    assert hasattr(shim, "resolve_saved_subgraph_tree")
+    assert hasattr(shim, "prepare_saved_subgraphs")
+
+
+def test_shim_symbols_are_identical_to_canonical() -> None:
+    assert shim.SavedSubgraphTree is canonical.SavedSubgraphTree
+    assert shim.resolve_saved_subgraph_tree is canonical.resolve_saved_subgraph_tree
+    assert shim.prepare_saved_subgraphs is canonical.prepare_saved_subgraphs
+    assert shim.validate_saved_subgraph_tree is canonical.validate_saved_subgraph_tree
+    assert (
+        shim.saved_subgraph_tree_from_snapshots
+        is canonical.saved_subgraph_tree_from_snapshots
+    )
+    assert (
+        shim.direct_wrapper_interrupt_diagnostic
+        is canonical.direct_wrapper_interrupt_diagnostic
+    )