feat: start new instances on python 3.15

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/windmill-worker/src/python_versions.rs

@@ -14,6 +14,7 @@ use tokio::{fs::DirBuilder, process::Command, sync::RwLock};
 use uuid::Uuid;
 use windmill_common::{
     error::{self, Error},
+    global_settings::{load_value_from_global_settings, INSTANCE_PYTHON_VERSION_SETTING},
     worker::{try_parse_locked_python_version_from_requirements, Connection, PyVAlias},
 };
 
@@ -256,7 +257,23 @@ impl PyV {
         conn: Option<Connection>,
     ) -> Self {
         let mut err = None;
-        let pyv = match INSTANCE_PYTHON_VERSION.read().await.clone() {
+        let mut setting = INSTANCE_PYTHON_VERSION.read().await.clone();
+        // A worker that loaded its settings while the server was still initializing the instance
+        // read no version, and may have started listening for setting changes only after it was
+        // written. Jobs only exist once it is, so reading it here settles that worker for good.
+        if setting.is_none() {
+            if let Some(Connection::Sql(db)) = conn.as_ref() {
+                setting = load_value_from_global_settings(db, INSTANCE_PYTHON_VERSION_SETTING)
+                    .await
+                    .ok()
+                    .flatten()
+                    .and_then(|v| serde_json::from_value::<String>(v).ok());
+                if setting.is_some() {
+                    *INSTANCE_PYTHON_VERSION.write().await = setting.clone();
+                }
+            }
+        }
+        let pyv = match setting {
             Some(v) if &v == "default" => PyVAlias::default().into(),
             Some(v) => pep440_rs::Version::from_str(&v).unwrap_or_else(|_| {
                 let v = PyVAlias::default().into();