fix(kotlin): emit implements edge for interface delegation (by)

class Foo : Bar by baz produced no edge because the delegation_specifier loop only handled constructor_invocation and bare user_type children; the by form wraps user_type in an explicit_delegation node. Add that branch so the implements edge (and generic-arg recovery) fires.

graphify/extract.py

@@ -3648,6 +3648,17 @@ def _extract_generic(
                             if sub.type == "user_type":
                                 user_type_node = sub
                                 break
+                            # `class Foo : Bar by baz` wraps the delegated
+                            # interface `Bar` in an `explicit_delegation`
+                            # node; grab its first `user_type` descendant so
+                            # the implements edge (and generic-arg recovery)
+                            # still fire.
+                            if sub.type == "explicit_delegation":
+                                for inner in sub.children:
+                                    if inner.type == "user_type":
+                                        user_type_node = inner
+                                        break
+                                break
                         if user_type_node is None:
                             continue
                         base = _kotlin_user_type_name(user_type_node, source)

tests/fixtures/sample.kt

@@ -35,6 +35,8 @@ class DataProcessor : BaseProcessor(), Loggable {
     override fun log() {}
 }
 
+class LoggingList<T>(inner: MutableList<T>) : MutableList<T> by inner
+
 fun createClient(baseUrl: String): HttpClient {
     val config = Config(baseUrl, 30)
     return HttpClient(config)

tests/test_languages.py

@@ -623,6 +623,13 @@ def test_kotlin_splits_inherits_and_implements():
     assert ("DataProcessor", "Loggable") in _edge_labels(r, "implements")
 
 
+def test_kotlin_interface_delegation_emits_implements():
+    """`class Foo : Bar by baz` wraps the delegated interface in an
+    `explicit_delegation` node — it must still emit an implements edge."""
+    r = extract_kotlin(FIXTURES / "sample.kt")
+    assert ("LoggingList", "MutableList") in _edge_labels(r, "implements")
+
+
 def test_kotlin_parameter_return_generic_and_field_contexts():
     r = extract_kotlin(FIXTURES / "sample.kt")
     assert ("run", "DataProcessor") in _edge_labels(r, "references", "parameter_type")