Omit unset optional request parameters

docs/integrations/openai-compatible-chat.md

@@ -53,8 +53,9 @@ never also sent as a session header.
 
 The client conditionally includes:
 
-- `temperature`, `max_tokens`, and `top_p` when non-zero or explicitly
-  present;
+- `temperature`, `max_tokens`, and `top_p` only when selected by a backend,
+  profile, or runtime override, including an explicit runtime zero; they are
+  absent when unspecified;
 - non-empty `service_tier` and effective `reasoning_effort`; an explicitly
   disabled reasoning setting is empty and therefore omitted; and
 - `response_format` for JSON Schema structured output, including its name,