fix(verify): resolve @payloadRef by FQN short-segment in verify --templates

FR-026 expands @payloadRef to a fully-qualified `a::b::Name`, but
`_resolve_payload_vo` (the verify --templates drift gate) matched only the bare
short `name` of the object.value child — so a templated prompt whose payloadRef
desugared to an FQN failed with "did not resolve to an object.value", even though
`gen` resolved it fine. Match the FQN's last segment too.

Regression surfaced by a downstream Python consumer; the conformance corpus didn't
cover an FQN-form @payloadRef against verify --templates.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: dmealing

server/python/src/metaobjects/codegen/generators/render_helper_generator.py

@@ -144,11 +144,14 @@ def _field_tree_literal(fields: list[PayloadField]) -> str:
 
 def _resolve_payload_vo(root: MetaData, payload_ref: str) -> MetaObject | None:
     """``@payloadRef`` must resolve to an ``object.value`` (same contract as the
-    parser/prompt generators). Bare short-name match on a value-object child."""
+    parser/prompt generators). Matches a value-object child by short name OR by the
+    last segment of a fully-qualified ``a::b::Name`` ref (FR-026 expands refs to FQN,
+    while the child node still carries the short ``name``)."""
+    ref_short = payload_ref.rsplit("::", 1)[-1]
     for child in root.own_children():
         if child.type != TYPE_OBJECT or not isinstance(child, MetaObject):
             continue
-        if child.sub_type == OBJECT_SUBTYPE_VALUE and child.name == payload_ref:
+        if child.sub_type == OBJECT_SUBTYPE_VALUE and child.name in (payload_ref, ref_short):
             return child
     return None
 

server/python/tests/codegen/test_render_helper_generator.py

@@ -25,6 +25,7 @@
 from metaobjects.codegen.generator import GenContext
 from metaobjects.codegen.generators.render_helper_generator import (
     RenderHelperGenerator,
+    _resolve_payload_vo,
     _snake_case,
     render_helper_generator,
 )
@@ -394,3 +395,24 @@ def test_generator_requires_template_root() -> None:
 def test_snake_case_pascal_to_snake() -> None:
     assert _snake_case("WelcomePage") == "welcome_page"
     assert _snake_case("Alpha") == "alpha"
+
+
+def test_resolve_payload_vo_matches_short_and_fully_qualified_ref() -> None:
+    """FR-026 expands @payloadRef to a fully-qualified ``a::b::Name`` while the
+    object.value child still carries the short ``name`` — both forms must resolve."""
+    import json
+
+    from metaobjects import InMemoryStringSource, MetaDataFormat, MetaDataLoader
+
+    root = MetaDataLoader().load([
+        InMemoryStringSource(
+            json.dumps({"metadata.root": {"package": "acme::blog", "children": [
+                {"object.value": {"name": "WelcomePayload",
+                                  "children": [{"field.string": {"name": "x"}}]}},
+            ]}}),
+            id="m.json", format=MetaDataFormat.JSON,
+        )
+    ]).root
+    assert _resolve_payload_vo(root, "WelcomePayload") is not None  # short ref
+    assert _resolve_payload_vo(root, "acme::blog::WelcomePayload") is not None  # FQN ref
+    assert _resolve_payload_vo(root, "acme::blog::Missing") is None