Fix regression in CallbackAdapter

Author: KoolADE85

dash/mcp/primitives/tools/callback_adapter.py

@@ -385,7 +385,7 @@ def _expand_output_spec(
     output_id: str,
     cb_info: dict,
     resolved_inputs: list[CallbackInput],
-) -> list[CallbackOutputTarget]:
+) -> CallbackOutputTarget | list[CallbackOutputTarget]:
     """Build the outputs spec, expanding wildcards to concrete IDs.
 
     For wildcard outputs, derives concrete IDs from the resolved inputs.
@@ -417,6 +417,11 @@ def _expand_output_spec(
         else:
             results.append({"id": pid, "property": prop})
 
+    # Mirror the Dash renderer: single-output callbacks send a bare dict,
+    # multi-output callbacks send a list. The framework's output value
+    # matching depends on this shape.
+    if len(results) == 1:
+        return results[0]
     return results
 
 

dash/mcp/primitives/tools/output_schemas/schema_callback_response.py

@@ -1,14 +1,14 @@
-"""Output schema derived from CallbackDispatchResponse."""
+"""Output schema derived from CallbackExecutionResponse."""
 
 from __future__ import annotations
 
 from typing import Any
 
 from pydantic import TypeAdapter
 
-from dash.types import CallbackDispatchResponse
+from dash.types import CallbackExecutionResponse
 
-_schema = TypeAdapter(CallbackDispatchResponse).json_schema()
+_schema = TypeAdapter(CallbackExecutionResponse).json_schema()
 
 
 def callback_response_schema() -> dict[str, Any]:

tests/unit/mcp/tools/test_tool_schema.py

@@ -15,7 +15,7 @@
 
 from pydantic import TypeAdapter
 from dash.development.base_component import Component
-from dash.types import CallbackDispatchResponse
+from dash.types import CallbackExecutionResponse
 
 _DASH_COMPONENT_SCHEMA = TypeAdapter(Component).json_schema()
 
@@ -51,7 +51,7 @@
             },
         },
     },
-    "outputSchema": TypeAdapter(CallbackDispatchResponse).json_schema(),
+    "outputSchema": TypeAdapter(CallbackExecutionResponse).json_schema(),
 }