fix: Deduplicate installed local and remote curated plugins (#25681)

## Summary
- Deduplicate installed `openai-curated` and `openai-curated-remote`
plugin conflicts by feature flag.
- Prefer remote when remote plugins are enabled; otherwise prefer local,
while preserving one-sided installs.

## Testing
- `just fmt`
- `git diff --check`
- Targeted `just test` was blocked locally because `cargo-nextest` is
not installed.

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

@@ -133,10 +133,14 @@ async fn load_config(codex_home: &Path, cwd: &Path) -> PluginsConfigInput {
 }
 
 fn remote_installed_linear_plugin() -> RemoteInstalledPlugin {
+    remote_installed_plugin("linear")
+}
+
+fn remote_installed_plugin(name: &str) -> RemoteInstalledPlugin {
     RemoteInstalledPlugin {
         marketplace_name: "openai-curated-remote".to_string(),
-        id: "plugins~Plugin_linear".to_string(),
-        name: "linear".to_string(),
+        id: format!("plugins~Plugin_{name}"),
+        name: name.to_string(),
         enabled: true,
         install_policy: codex_app_server_protocol::PluginInstallPolicy::Available,
         auth_policy: codex_app_server_protocol::PluginAuthPolicy::OnUse,
@@ -146,6 +150,18 @@ fn remote_installed_linear_plugin() -> RemoteInstalledPlugin {
     }
 }
 
+fn write_cached_plugin(codex_home: &Path, marketplace_name: &str, plugin_name: &str) {
+    write_plugin_with_version(
+        &codex_home
+            .join("plugins/cache")
+            .join(marketplace_name)
+            .join(plugin_name),
+        "local",
+        plugin_name,
+        /*manifest_version*/ Some("local"),
+    );
+}
+
 #[tokio::test]
 async fn load_plugins_loads_default_skills_and_mcp_servers() {
     let codex_home = TempDir::new().unwrap();
@@ -352,6 +368,92 @@ remote_plugin = true
     assert_eq!(outcome, PluginLoadOutcome::default());
 }
 
+#[tokio::test]
+async fn remote_installed_cache_prefers_local_curated_conflicts_when_remote_plugin_disabled() {
+    let codex_home = TempDir::new().unwrap();
+    write_file(
+        &codex_home.path().join(CONFIG_TOML_FILE),
+        r#"[features]
+plugins = true
+remote_plugin = false
+
+[plugins."linear@openai-curated"]
+enabled = true
+
+[plugins."calendar@openai-curated"]
+enabled = true
+"#,
+    );
+    write_cached_plugin(codex_home.path(), "openai-curated", "linear");
+    write_cached_plugin(codex_home.path(), "openai-curated", "calendar");
+    write_cached_plugin(codex_home.path(), "openai-curated-remote", "linear");
+    write_cached_plugin(codex_home.path(), "openai-curated-remote", "remote-only");
+
+    let config = load_config(codex_home.path(), codex_home.path()).await;
+    let manager = PluginsManager::new(codex_home.path().to_path_buf());
+    manager.write_remote_installed_plugins_cache(vec![
+        remote_installed_plugin("linear"),
+        remote_installed_plugin("remote-only"),
+    ]);
+
+    let outcome = manager.plugins_for_config(&config).await;
+    assert_eq!(
+        outcome
+            .plugins()
+            .iter()
+            .map(|plugin| plugin.config_name.clone())
+            .collect::<Vec<_>>(),
+        vec![
+            "calendar@openai-curated".to_string(),
+            "linear@openai-curated".to_string(),
+            "remote-only@openai-curated-remote".to_string(),
+        ]
+    );
+}
+
+#[tokio::test]
+async fn remote_installed_cache_prefers_remote_curated_conflicts_when_remote_plugin_enabled() {
+    let codex_home = TempDir::new().unwrap();
+    write_file(
+        &codex_home.path().join(CONFIG_TOML_FILE),
+        r#"[features]
+plugins = true
+remote_plugin = true
+
+[plugins."linear@openai-curated"]
+enabled = true
+
+[plugins."calendar@openai-curated"]
+enabled = true
+"#,
+    );
+    write_cached_plugin(codex_home.path(), "openai-curated", "linear");
+    write_cached_plugin(codex_home.path(), "openai-curated", "calendar");
+    write_cached_plugin(codex_home.path(), "openai-curated-remote", "linear");
+    write_cached_plugin(codex_home.path(), "openai-curated-remote", "remote-only");
+
+    let config = load_config(codex_home.path(), codex_home.path()).await;
+    let manager = PluginsManager::new(codex_home.path().to_path_buf());
+    manager.write_remote_installed_plugins_cache(vec![
+        remote_installed_plugin("linear"),
+        remote_installed_plugin("remote-only"),
+    ]);
+
+    let outcome = manager.plugins_for_config(&config).await;
+    assert_eq!(
+        outcome
+            .plugins()
+            .iter()
+            .map(|plugin| plugin.config_name.clone())
+            .collect::<Vec<_>>(),
+        vec![
+            "calendar@openai-curated".to_string(),
+            "linear@openai-curated-remote".to_string(),
+            "remote-only@openai-curated-remote".to_string(),
+        ]
+    );
+}
+
 #[tokio::test]
 async fn build_remote_installed_plugin_marketplaces_from_cache_uses_remote_metadata() {
     let codex_home = TempDir::new().unwrap();
@@ -3713,6 +3815,7 @@ async fn load_plugins_ignores_project_config_files() {
         std::collections::HashMap::new(),
         &PluginStore::new(codex_home.path().to_path_buf()),
         Some(Product::Codex),
+        /*prefer_remote_curated_conflicts*/ false,
     )
     .await;