Replace --python-preference installed with managed

Collapses the previous default into "managed" and makes the "managed" behavior match "installed". People should use "only-managed" if they want that behavior, it seems overly complicated otherwise.

crates/uv-python/src/discovery.rs

@@ -61,12 +61,11 @@ pub enum PythonRequest {
 pub enum PythonPreference {
     /// Only use managed Python installations; never use system Python installations.
     OnlyManaged,
-    /// Prefer installed Python installations, only download managed Python installations if no system Python installation is found.
-    ///
-    /// Installed managed Python installations are still preferred over system Python installations.
     #[default]
-    Installed,
-    /// Prefer managed Python installations over system Python installations, even if fetching is required.
+    /// Prefer managed Python installations over system Python installations.
+    ///
+    /// System Python versions are still preferred over downloading managed Python installations.
+    /// Use `only-managed` to always fetch a managed Python version.
     Managed,
     /// Prefer system Python installations over managed Python installations.
     ///
@@ -305,7 +304,7 @@ fn python_executables_from_installed<'a>(
 
     match preference {
         PythonPreference::OnlyManaged => Box::new(from_managed_installations),
-        PythonPreference::Managed | PythonPreference::Installed => Box::new(
+        PythonPreference::Managed => Box::new(
             from_managed_installations
                 .chain(from_search_path)
                 .chain(from_py_launcher),
@@ -1272,7 +1271,7 @@ impl PythonPreference {
 
         match self {
             PythonPreference::OnlyManaged => matches!(source, PythonSource::Managed),
-            Self::Managed | Self::System | Self::Installed => matches!(
+            Self::Managed | Self::System => matches!(
                 source,
                 PythonSource::Managed | PythonSource::SearchPath | PythonSource::PyLauncher
             ),
@@ -1295,7 +1294,7 @@ impl PythonPreference {
     }
 
     pub(crate) fn allows_managed(self) -> bool {
-        matches!(self, Self::Managed | Self::OnlyManaged | Self::Installed)
+        matches!(self, Self::Managed | Self::OnlyManaged)
     }
 }
 
@@ -1603,7 +1602,7 @@ impl PythonPreference {
     fn sources(self) -> &'static [&'static str] {
         match self {
             Self::OnlyManaged => &["managed installations"],
-            Self::Managed | Self::Installed | Self::System => {
+            Self::Managed | Self::System => {
                 if cfg!(windows) {
                     &["managed installations", "system path", "`py` launcher"]
                 } else {

crates/uv-python/src/installation.rs

@@ -88,13 +88,6 @@ impl PythonInstallation {
     ) -> Result<Self, Error> {
         let request = request.unwrap_or_default();
 
-        // Perform a fetch aggressively if managed Python is preferred
-        if matches!(preference, PythonPreference::Managed) && python_fetch.is_automatic() {
-            if let Some(request) = PythonDownloadRequest::from_request(&request) {
-                return Self::fetch(request.fill(), client_builder, cache, reporter).await;
-            }
-        }
-
         // Search for the installation
         match Self::find(&request, environments, preference, cache) {
             Ok(venv) => Ok(venv),

docs/settings.md

@@ -648,8 +648,7 @@ those that are downloaded and installed by uv.
 **Possible values**:
 
 - `"only-managed"`: Only use managed Python installations; never use system Python installations
-- `"installed"`: Prefer installed Python installations, only download managed Python installations if no system Python installation is found
-- `"managed"`: Prefer managed Python installations over system Python installations, even if fetching is required
+- `"managed"`: Prefer managed Python installations over system Python installations
 - `"system"`: Prefer system Python installations over managed Python installations
 - `"only-system"`: Only use system Python installations; never use managed Python installations