https://github.com/neondatabase/neon/pull/12676#discussion_r2220512343; concern about backward compat of TimelineInfo

libs/pageserver_api/src/models.rs

@@ -1623,6 +1623,7 @@ pub struct TimelineInfo {
     /// Whether the timeline is invisible in synthetic size calculations.
     pub is_invisible: Option<bool>,
 
+    #[serde(default)]
     pub standby_horizon: serde_json::Value,
 }