fix(structural): preserve decorator declaration provenance

diffgraph/structural.py

@@ -290,15 +290,27 @@ def visit(node, parents: Tuple[Tuple[str, str], ...] = ()) -> None:
                     if occurrence == 0
                     else "{}#{}".format(base_qname, occurrence)
                 )
-                body = content[node.start_byte:node.end_byte]
+                # Tree-sitter wraps decorated declarations in a
+                # ``decorated_definition`` node. The decorator is part of the
+                # declaration's exact source-level behavior, so include that
+                # wrapper in the symbol span and hash. Otherwise changing
+                # ``@decorator`` could incorrectly leave the declaration
+                # unchanged in a deterministic DiffGraph artifact.
+                declaration = (
+                    node.parent
+                    if node.parent is not None
+                    and node.parent.type == "decorated_definition"
+                    else node
+                )
+                body = content[declaration.start_byte:declaration.end_byte]
                 symbols.append(
                     _Symbol(
                         name,
                         qname,
                         kind,
                         parent,
-                        node.start_point[0] + 1,
-                        node.end_point[0] + 1,
+                        declaration.start_point[0] + 1,
+                        declaration.end_point[0] + 1,
                         hashlib.sha256(body).hexdigest(),
                     )
                 )

tests/test_structural.py

@@ -1442,3 +1442,33 @@ def test_later_import_does_not_hide_earlier_local_call(tmp_path):
     assert len(calls) == 1
     assert calls[0]["target_id"] == "sym::local_before_import.py::run"
     assert calls[0]["resolution_method"] == "resolved"
+
+
+def test_decorator_change_is_part_of_python_declaration_evidence(tmp_path):
+    """Decorator edits modify the wrapped declaration rather than disappearing."""
+    root = repo(tmp_path)
+    write(
+        root,
+        "decorated.py",
+        "@first\ndef decorated():\n    return 1\n",
+    )
+    commit(root)
+    write(
+        root,
+        "decorated.py",
+        "@second\ndef decorated():\n    return 1\n",
+    )
+
+    artifact = analyze_local_diff(str(root))
+
+    assert_valid(artifact)
+    symbol = next(item for item in artifact["symbols"] if item["name"] == "decorated")
+    assert symbol["kind"] == "function"
+    assert symbol["change_kind"] == "modified"
+    assert symbol["evidence"] == [{
+        "kind": "ast_parse",
+        "file": "decorated.py",
+        "line_start": 1,
+        "line_end": 3,
+        "detail": symbol["evidence"][0]["detail"],
+    }]