fix(csharp): extract delegate declarations so references don't mint sourceless stubs

A C# `delegate` is a named type, but `delegate_declaration` was in neither
`class_types` nor `function_types`, so the declaration was dropped from the
graph. A field or parameter typed as the delegate (`public BinOp Op;`,
`int Apply(BinOp f, ...)`) still resolved the name `BinOp` through
`ensure_named_node`, which minted a *sourceless* stub and pointed the
`references` edge at it — even though `BinOp` is declared in the same file.

That violates the provenance invariant: a real source-backed declaration must
not lose to a sourceless god node (and the bare-id stub becomes a cross-file
hub shared by every same-named reference in the corpus).

`delegate_declaration` has a `name` field and no body, so adding it to the C#
`class_types` emits a clean empty type node (no phantom members) that the
in-file references now bind to. Namespaced delegates are scoped and contained
exactly like the sibling class/enum/struct declarations.

Delegate parameter/return type references and delegate-instance invocation
resolution are unchanged (out of scope).

graphify/extract.py

@@ -1520,6 +1520,13 @@ _CSHARP_CONFIG = LanguageConfig(
         "enum_declaration",
         "struct_declaration",
         "record_declaration",
+        # A `delegate` is a named type. Without it the declaration was dropped,
+        # yet in-file references to the delegate type (a `BinOp` field/parameter)
+        # still ran through `ensure_named_node` and minted a *sourceless* stub —
+        # a provenance violation (a real in-file type losing to a sourceless god
+        # node). It has a `name` field and no body, so it emits a clean empty
+        # type node that those references bind to.
+        "delegate_declaration",
     }),
     function_types=frozenset({"method_declaration"}),
     import_types=frozenset({"using_directive"}),

tests/test_csharp_delegate_declarations.py

@@ -0,0 +1,70 @@
+"""A C# `delegate` is a named type and must be extracted as a sourced node.
+
+`public delegate int BinOp(int a, int b);` was in neither `class_types` nor
+`function_types`, so the declaration was dropped. But a field or parameter typed
+as the delegate (`BinOp Op;`) still ran the name `BinOp` through
+`ensure_named_node`, which minted a *sourceless* stub node and pointed the
+`references` edge at it — even though `BinOp` is declared in the very same file.
+That is a provenance violation (a real source-backed declaration losing to a
+sourceless god node). Adding `delegate_declaration` to the C# `class_types` emits
+a clean empty type node (it has a `name` field and no body) that the in-file
+references bind to instead.
+"""
+from __future__ import annotations
+
+from pathlib import Path
+
+from graphify.extract import extract
+
+
+def _extract(tmp_path, body: str):
+    (tmp_path / "d.cs").write_text(body)
+    return extract([tmp_path / "d.cs"], cache_root=tmp_path, parallel=False)
+
+
+def _node(r, label):
+    return next((n for n in r["nodes"] if n.get("label") == label), None)
+
+
+def test_delegate_is_a_sourced_node_not_a_sourceless_stub(tmp_path):
+    r = _extract(
+        tmp_path,
+        "public delegate int BinOp(int a, int b);\n"
+        "public class Calc {\n"
+        "    public BinOp Op;\n"
+        "    public int Apply(BinOp f, int x) { return f(x, x); }\n"
+        "}\n",
+    )
+    binop = _node(r, "BinOp")
+    assert binop is not None, "delegate declaration was dropped"
+    assert binop.get("source_file"), (
+        f"delegate BinOp is a sourceless god node: {binop}"
+    )
+    # No sourceless node is left over for a type that is declared in-file.
+    assert not any(
+        (not n.get("source_file")) and n.get("label") == "BinOp"
+        for n in r["nodes"]
+    )
+    # The field/parameter references now bind to the real sourced delegate node.
+    refs_to_binop = {
+        e["source"]
+        for e in r["edges"]
+        if e["relation"] == "references" and e["target"] == binop["id"]
+    }
+    assert refs_to_binop, "references to the delegate did not bind to it"
+
+
+def test_namespaced_delegate_is_scoped_and_sourced(tmp_path):
+    r = _extract(
+        tmp_path,
+        "namespace App {\n"
+        "    public delegate void Handler(string msg);\n"
+        "    public class Bus { public Handler OnMsg; }\n"
+        "}\n",
+    )
+    handler = _node(r, "Handler")
+    assert handler is not None and handler.get("source_file")
+    assert any(
+        e["relation"] == "references" and e["target"] == handler["id"]
+        for e in r["edges"]
+    )