refactor(plugins): simplify stale-version prune guard

codex-rs/core-plugins/src/store.rs

@@ -286,6 +286,15 @@ fn replace_plugin_root_atomically(
     let staged_version_root = staged_root.join(plugin_version);
     copy_dir_recursive(source, &staged_version_root)?;
 
+    let target_version_root = target_root.join(plugin_version);
+    if target_root.exists() && !target_version_root.exists() {
+        fs::rename(&staged_version_root, &target_version_root).map_err(|err| {
+            PluginStoreError::io("failed to activate updated plugin cache version", err)
+        })?;
+        remove_old_plugin_versions(target_root, plugin_version)?;
+        return Ok(());
+    }
+
     if target_root.exists() {
         let backup_dir = tempfile::Builder::new()
             .prefix("plugin-backup-")
@@ -322,6 +331,44 @@ fn replace_plugin_root_atomically(
     Ok(())
 }
 
+fn remove_old_plugin_versions(
+    target_root: &Path,
+    plugin_version: &str,
+) -> Result<(), PluginStoreError> {
+    let Ok(entries) = fs::read_dir(target_root) else {
+        return Ok(());
+    };
+
+    for entry in entries.filter_map(Result::ok) {
+        let Ok(file_type) = entry.file_type() else {
+            continue;
+        };
+        if !file_type.is_dir() {
+            continue;
+        }
+        let Ok(version) = entry.file_name().into_string() else {
+            continue;
+        };
+        if version == plugin_version || validate_plugin_version_segment(&version).is_err() {
+            continue;
+        }
+
+        if fs::remove_dir_all(entry.path()).is_err()
+            && old_plugin_version_would_stay_active(&version, plugin_version)
+        {
+            return Err(PluginStoreError::Invalid(format!(
+                "failed to activate updated plugin cache version `{plugin_version}` while `{version}` remains active"
+            )));
+        }
+    }
+
+    Ok(())
+}
+
+fn old_plugin_version_would_stay_active(old_version: &str, new_version: &str) -> bool {
+    old_version == DEFAULT_PLUGIN_VERSION || old_version > new_version
+}
+
 fn copy_dir_recursive(source: &Path, target: &Path) -> Result<(), PluginStoreError> {
     fs::create_dir_all(target)
         .map_err(|err| PluginStoreError::io("failed to create plugin target directory", err))?;

codex-rs/core-plugins/src/store_tests.rs

@@ -268,6 +268,54 @@ fn active_plugin_version_returns_last_sorted_version_when_default_is_missing() {
     );
 }
 
+#[test]
+fn install_with_new_version_keeps_existing_plugin_root_and_prunes_old_versions() {
+    let tmp = tempdir().unwrap();
+    let store = PluginStore::new(tmp.path().to_path_buf());
+    let plugin_id = PluginId::new("sample-plugin".to_string(), "debug".to_string()).unwrap();
+
+    write_plugin_with_version(tmp.path(), "v1", "sample-plugin", Some("1.0.0"));
+    store
+        .install(
+            AbsolutePathBuf::try_from(tmp.path().join("v1")).unwrap(),
+            plugin_id.clone(),
+        )
+        .unwrap();
+
+    write_plugin_with_version(tmp.path(), "v2", "sample-plugin", Some("2.0.0"));
+    store
+        .install(
+            AbsolutePathBuf::try_from(tmp.path().join("v2")).unwrap(),
+            plugin_id.clone(),
+        )
+        .unwrap();
+
+    assert_eq!(
+        store.active_plugin_version(&plugin_id),
+        Some("2.0.0".to_string())
+    );
+    assert!(
+        tmp.path()
+            .join("plugins/cache/debug/sample-plugin/2.0.0")
+            .is_dir()
+    );
+    assert!(
+        !tmp.path()
+            .join("plugins/cache/debug/sample-plugin/1.0.0")
+            .exists()
+    );
+}
+
+#[test]
+fn old_plugin_version_would_stay_active_for_local_or_later_versions() {
+    assert!(old_plugin_version_would_stay_active(
+        DEFAULT_PLUGIN_VERSION,
+        "1.0.0"
+    ));
+    assert!(old_plugin_version_would_stay_active("9.0.0", "1.0.0"));
+    assert!(!old_plugin_version_would_stay_active("1.0.0", "2.0.0"));
+}
+
 #[test]
 fn plugin_root_rejects_path_separators_in_key_segments() {
     let err = PluginId::parse("../../etc@debug").unwrap_err();