fix(kagent-adk): compact MCP App tool results only when the result carries a UI resource

python/packages/kagent-adk/src/kagent/adk/_mcp_apps.py

@@ -54,19 +54,39 @@ def __len__(self) -> int:
         return len(self._names)
 
 
+def _result_has_ui_resource(response: dict) -> bool:
+    """Whether this specific result, not just the tool's definition, carries a UI resource.
+
+    Mirrors the ``_meta.ui.resourceUri`` / ``_meta["ui/resourceUri"]`` parsing already
+    used to classify a tool's definition (``go/adk/pkg/mcp/mcp_ui.go:parseMCPUIMetadata``).
+    """
+    meta = response.get("_meta")
+    if not isinstance(meta, dict):
+        return False
+    ui = meta.get("ui")
+    if isinstance(ui, dict) and ui.get("resourceUri"):
+        return True
+    return bool(meta.get("ui/resourceUri"))
+
+
 def compact_mcp_app_response(response: dict) -> dict:
     """Rewrite an MCP App tool result (a JSON ``CallToolResult``) for the model.
 
     On error, keep the content so the model can diagnose/recover but drop the
     heavy structured payload. On success, collapse the render payload into a
     terminal directive so the model stops re-invoking the rendering tool,
-    preserving ``_meta`` (e.g. resourceUri) for any downstream tooling.
+    preserving ``_meta`` (e.g. resourceUri) for any downstream tooling. A tool
+    can be UI-capable by definition yet return a plain result for a given
+    call; only compact when this result itself carries a UI resource.
     """
     if response.get("isError") is True or response.get("error") is True:
         compacted = dict(response)
         compacted.pop("structuredContent", None)
         return compacted
 
+    if not _result_has_ui_resource(response):
+        return response
+
     compacted: dict = {"content": [{"type": "text", "text": MCP_APP_RENDERED_NOTICE}]}
     if "_meta" in response:
         compacted["_meta"] = response["_meta"]

python/packages/kagent-adk/tests/unittests/test_mcp_apps.py

@@ -31,6 +31,24 @@ def test_compact_success_replaces_payload_with_notice():
     assert compacted["_meta"] == response["_meta"]
 
 
+def test_compact_skips_data_only_result_from_a_ui_capable_tool():
+    # A UI-capable tool's result with no UI resource of its own.
+    response = {
+        "content": [{"type": "text", "text": '{"issues": [{"key": "GF-3687"}]}'}],
+        "structuredContent": {"issues": [{"key": "GF-3687"}]},
+        "_meta": {},
+    }
+    compacted = compact_mcp_app_response(response)
+    assert compacted == response
+
+
+def test_compact_skips_result_with_no_meta_at_all():
+    # Servers that never set _meta on a call result (as opposed to an empty one).
+    response = {"content": [{"type": "text", "text": "hello"}], "structuredContent": {"x": 1}}
+    compacted = compact_mcp_app_response(response)
+    assert compacted == response
+
+
 def test_compact_error_keeps_content_drops_structured():
     response = {
         "content": [{"type": "text", "text": "boom"}],
@@ -48,7 +66,11 @@ def test_callback_compacts_only_app_tool_responses():
     app_tool_names.add("show-weather-dashboard")
     callback = make_mcp_app_model_result_callback(app_tool_names)
 
-    weather = {"structuredContent": {"temperature": 36}, "content": [{"type": "text", "text": "36C"}]}
+    weather = {
+        "structuredContent": {"temperature": 36},
+        "content": [{"type": "text", "text": "36C"}],
+        "_meta": {"ui": {"resourceUri": "ui://server-everything/weather-dashboard"}},
+    }
     echo = {"content": [{"type": "text", "text": "hello"}]}
     request = LlmRequest(
         contents=[