[codex] [4/4] Simplify recommended plugin install schema (#28403)

## Summary
- Simplify recommendation-context `request_plugin_install` arguments to
`plugin_id` and `suggest_reason`.
- Derive plugin type and install action from the matched candidate while
preserving Codex-owned elicitation metadata.
- Keep the legacy list-backed schema unchanged and accept resumed calls
that still use `tool_id`.

## Stack
- #28399
- #28400
- #27704
- This PR

## Validation
- `just test -p codex-tools -p codex-core request_plugin_install` (25
passed)
- `just fix -p codex-tools -p codex-core`
- `just fmt`
- `git diff --check`

codex-rs/tools/src/request_plugin_install.rs

@@ -57,7 +57,6 @@ pub fn build_request_plugin_install_elicitation_request(
     server_name: &str,
     thread_id: String,
     turn_id: String,
-    args: &RequestPluginInstallArgs,
     suggest_reason: &str,
     tool: &DiscoverableTool,
 ) -> McpServerElicitationRequestParams {
@@ -69,8 +68,6 @@ pub fn build_request_plugin_install_elicitation_request(
         server_name: server_name.to_string(),
         request: McpServerElicitationRequest::Form {
             meta: Some(json!(build_request_plugin_install_meta(
-                args.tool_type,
-                args.action_type,
                 suggest_reason,
                 tool,
             ))),
@@ -105,14 +102,13 @@ pub fn verified_connector_install_completed(
 }
 
 fn build_request_plugin_install_meta<'a>(
-    tool_type: DiscoverableToolType,
-    action_type: DiscoverableToolAction,
     suggest_reason: &'a str,
     tool: &'a DiscoverableTool,
 ) -> RequestPluginInstallMeta<'a> {
-    let (remote_plugin_id, app_connector_ids) = match tool {
-        DiscoverableTool::Connector(_) => (None, None),
+    let (tool_type, remote_plugin_id, app_connector_ids) = match tool {
+        DiscoverableTool::Connector(_) => (DiscoverableToolType::Connector, None, None),
         DiscoverableTool::Plugin(plugin) => (
+            DiscoverableToolType::Plugin,
             plugin.remote_plugin_id.as_deref(),
             Some(plugin.app_connector_ids.as_slice()),
         ),
@@ -121,7 +117,7 @@ fn build_request_plugin_install_meta<'a>(
         codex_approval_kind: REQUEST_PLUGIN_INSTALL_APPROVAL_KIND_VALUE,
         persist: REQUEST_PLUGIN_INSTALL_PERSIST_ALWAYS_VALUE,
         tool_type,
-        suggest_type: action_type,
+        suggest_type: DiscoverableToolAction::Install,
         suggest_reason,
         tool_id: tool.id(),
         tool_name: tool.name(),

codex-rs/tools/src/request_plugin_install_tests.rs

@@ -5,12 +5,6 @@ use serde_json::json;
 
 #[test]
 fn build_request_plugin_install_elicitation_request_uses_expected_shape() {
-    let args = RequestPluginInstallArgs {
-        tool_type: DiscoverableToolType::Connector,
-        action_type: DiscoverableToolAction::Install,
-        tool_id: "connector_2128aebfecb84f64a069897515042a44".to_string(),
-        suggest_reason: "Plan and reference events from your calendar".to_string(),
-    };
     let connector = DiscoverableTool::Connector(Box::new(AppInfo {
         id: "connector_2128aebfecb84f64a069897515042a44".to_string(),
         name: "Google Calendar".to_string(),
@@ -34,7 +28,6 @@ fn build_request_plugin_install_elicitation_request_uses_expected_shape() {
         "codex-apps",
         "thread-1".to_string(),
         "turn-1".to_string(),
-        &args,
         "Plan and reference events from your calendar",
         &connector,
     );
@@ -74,12 +67,6 @@ fn build_request_plugin_install_elicitation_request_uses_expected_shape() {
 
 #[test]
 fn build_request_plugin_install_elicitation_request_injects_plugin_metadata() {
-    let args = RequestPluginInstallArgs {
-        tool_type: DiscoverableToolType::Plugin,
-        action_type: DiscoverableToolAction::Install,
-        tool_id: "sample@openai-curated-remote".to_string(),
-        suggest_reason: "Use the sample plugin's skills and MCP server".to_string(),
-    };
     let plugin = DiscoverableTool::Plugin(Box::new(DiscoverablePluginInfo {
         id: "sample@openai-curated-remote".to_string(),
         remote_plugin_id: Some("plugins~Plugin_sample".to_string()),
@@ -94,7 +81,6 @@ fn build_request_plugin_install_elicitation_request_injects_plugin_metadata() {
         "codex-apps",
         "thread-1".to_string(),
         "turn-1".to_string(),
-        &args,
         "Use the sample plugin's skills and MCP server",
         &plugin,
     );
@@ -149,12 +135,8 @@ fn build_request_plugin_install_meta_uses_expected_shape() {
         is_enabled: true,
         plugin_display_names: Vec::new(),
     }));
-    let meta = build_request_plugin_install_meta(
-        DiscoverableToolType::Connector,
-        DiscoverableToolAction::Install,
-        "Find and reference emails from your inbox",
-        &connector,
-    );
+    let meta =
+        build_request_plugin_install_meta("Find and reference emails from your inbox", &connector);
 
     assert_eq!(
         meta,