Close the f-string in Prompt.render and pin the shorter message

The applied suggestion dropped the closing quote along with the
interpolated exception text, so prompts/base.py no longer parsed. With
the message now just "Error rendering prompt <name>", the legacy-path
interaction test snapshots that instead of matching the pydantic prefix.

Author: maxisbey

src/mcp/server/mcpserver/prompts/base.py

@@ -210,4 +210,4 @@ async def render(
         except MCPError:
             raise
         except Exception as exc:
-            raise ValueError(f"Error rendering prompt {self.name}) from exc
+            raise ValueError(f"Error rendering prompt {self.name}") from exc

tests/interaction/mcpserver/test_prompts.py

@@ -123,8 +123,8 @@ async def test_get_prompt_with_a_wrong_type_argument_is_rejected_before_the_func
 
     The decorated function is wrapped in pydantic's validate_call, so a value that cannot be
     coerced to the parameter's annotation fails before the body executes. The function body
-    raises NotImplementedError to prove it never ran. The error is wrapped in the SDK's stable
-    rendering-error prefix; the body of the message is raw pydantic output and is not asserted.
+    raises NotImplementedError to prove it never ran. The client sees only the SDK's
+    rendering-error message naming the prompt, with the pydantic detail withheld.
     """
     mcp = MCPServer("prompter")
 
@@ -137,8 +137,7 @@ def repeat(phrase: str, count: int) -> str:
         with pytest.raises(MCPError) as exc_info:
             await client.get_prompt("repeat", {"phrase": "hi", "count": "many"})
 
-    assert exc_info.value.error.code == 0
-    assert exc_info.value.error.message.startswith("Error rendering prompt repeat: 1 validation error")
+    assert exc_info.value.error == snapshot(ErrorData(code=0, message="Error rendering prompt repeat"))
 
 
 @requirement("mcpserver:prompt:optional-args")