fix(go): preserve interface method signature references

(cherry picked from commit 00fb309983)

graphify/extractors/go.py

@@ -390,6 +390,7 @@ def extract_go(path: Path) -> dict:
                             m_nid = symbol_nid(_make_id(type_nid, m_name), m_name)
                             add_node(m_nid, f".{m_name}()", m_line)
                             add_edge(type_nid, m_nid, "method", m_line)
+                            emit_go_method_refs(elem, m_nid, m_line)
                             continue
                         if elem.type != "type_elem":
                             continue

tests/test_go_interface_methods.py

@@ -8,6 +8,8 @@ an empty node with no members - the method requirements were dropped entirely.
 
 from pathlib import Path
 
+import pytest
+
 from graphify.extract import extract
 
 
@@ -106,3 +108,60 @@ def test_interface_method_is_distinct_from_a_concrete_method(tmp_path: Path) ->
     }
     assert shape_area and rect_area
     assert shape_area.isdisjoint(rect_area), "interface and struct methods collapsed"
+
+
+def _signature_refs(result: dict, owner_label: str) -> tuple[str, list[dict]]:
+    by_id = {node["id"]: node for node in result["nodes"]}
+    method_ids = {
+        edge["target"]
+        for edge in result["edges"]
+        if edge.get("relation") == "method"
+        and by_id[edge["source"]].get("label") == owner_label
+    }
+    assert len(method_ids) == 1
+    method_id = method_ids.pop()
+    return method_id, [
+        {**edge, "target_label": by_id[edge["target"]]["label"]}
+        for edge in result["edges"]
+        if edge.get("relation") == "references" and edge["source"] == method_id
+    ]
+
+
+@pytest.mark.parametrize(
+    ("signature", "body"),
+    [
+        ("Handle(Request) Response", "return Response{}"),
+        ("Handle(req *Request) (res *Response, err error)", "return nil, nil"),
+    ],
+)
+def test_interface_method_signature_keeps_type_references(tmp_path: Path, signature, body):
+    path = tmp_path / "contract.go"
+    path.write_text(
+        "package contracts\n\n"
+        "type Request struct{}\n"
+        "type Response struct{}\n"
+        "type Service interface {\n"
+        f"    {signature}\n"
+        "}\n\n"
+        "type Impl struct{}\n"
+        f"func (Impl) {signature} {{ {body} }}\n",
+        encoding="utf-8",
+    )
+    result = _extract(tmp_path)
+    interface_id, interface_refs = _signature_refs(result, "Service")
+    concrete_id, concrete_refs = _signature_refs(result, "Impl")
+    expected = {("Request", "parameter_type"), ("Response", "return_type")}
+    assert {(edge["target_label"], edge["context"]) for edge in concrete_refs} == expected
+    assert {(edge["target_label"], edge["context"]) for edge in interface_refs} == expected
+    assert len(interface_refs) == 2
+    assert interface_id != concrete_id
+    assert not any(node["label"] == "error" for node in result["nodes"])
+    for edge in interface_refs:
+        assert edge["source_file"] == "contract.go"
+        assert edge["source_location"] == "L6"
+        assert edge["confidence"] == "EXTRACTED"
+
+    # A warm extraction replays the same source-owned signature edges.
+    warm = _extract(tmp_path)
+    assert _signature_refs(warm, "Service") == (interface_id, interface_refs)
+    assert _signature_refs(warm, "Impl") == (concrete_id, concrete_refs)