[codex] [2/4] Generalize plugin suggestion presentation (#28400)

Summary
- Add list-backed and developer-context presentations for plugin
suggestion candidates.
- Let tool planning, install validation, and request-tool copy follow
the selected presentation.
- Keep every production caller on the existing list-backed presentation,
preserving the current list tool, request schema, connector behavior,
and model-visible copy.
- Leave developer-context presentation latent until the final PR in the
stack.

Stack
- 2/3, based on #28399.
- Follow-up: #27704 activates endpoint recommendations.

Validation
- `just test -p codex-core request_plugin_install`
- `just test -p codex-core spec_plan`
- `just fix -p codex-core`
- `just fmt`
- `git diff --check`

codex-rs/core/src/session/tests.rs

@@ -571,9 +571,9 @@ fn test_tool_runtime(session: Arc<Session>, turn_context: Arc<TurnContext>) -> T
     let router = Arc::new(ToolRouter::from_turn_context(
         &turn_context,
         crate::tools::router::ToolRouterParams {
+            tool_suggest_candidates: None,
             mcp_tools: None,
             deferred_mcp_tools: None,
-            discoverable_tools: None,
             extension_tool_executors: Vec::new(),
             dynamic_tools: turn_context.dynamic_tools.as_slice(),
         },
@@ -9600,9 +9600,9 @@ async fn fatal_tool_error_stops_turn_and_reports_error() {
     let router = ToolRouter::from_turn_context(
         &turn_context,
         crate::tools::router::ToolRouterParams {
+            tool_suggest_candidates: None,
             deferred_mcp_tools,
             mcp_tools: Some(tools),
-            discoverable_tools: None,
             extension_tool_executors: Vec::new(),
             dynamic_tools: turn_context.dynamic_tools.as_slice(),
         },

codex-rs/core/src/session/turn.rs

@@ -58,6 +58,8 @@ use crate::tools::context::SharedTurnDiffTracker;
 use crate::tools::parallel::ToolCallRuntime;
 use crate::tools::registry::ToolArgumentDiffConsumer;
 use crate::tools::router::ToolRouterParams;
+use crate::tools::router::ToolSuggestCandidates;
+use crate::tools::router::ToolSuggestPresentation;
 use crate::tools::router::extension_tool_executors;
 use crate::tools::spec_plan::search_tool_enabled;
 use crate::tools::spec_plan::tool_suggest_enabled;
@@ -1190,7 +1192,7 @@ pub(crate) async fn built_tools(
         .into_iter()
         .map(|connector_id| connector_id.0)
         .collect::<Vec<_>>();
-    let discoverable_tools = async {
+    let tool_suggest_candidates = async {
         if apps_enabled && tool_suggest_enabled(turn_context) {
             if let Some(accessible_connectors) = accessible_connectors_with_enabled_state.as_ref() {
                 match connectors::list_tool_suggest_discoverable_tools_with_auth(
@@ -1208,7 +1210,10 @@ pub(crate) async fn built_tools(
                     )
                 }) {
                     Ok(discoverable_tools) if discoverable_tools.is_empty() => None,
-                    Ok(discoverable_tools) => Some(discoverable_tools),
+                    Ok(discoverable_tools) => Some(ToolSuggestCandidates {
+                        tools: discoverable_tools,
+                        presentation: ToolSuggestPresentation::ListTool,
+                    }),
                     Err(err) => {
                         warn!("failed to load discoverable tool suggestions: {err:#}");
                         None
@@ -1237,7 +1242,7 @@ pub(crate) async fn built_tools(
         ToolRouterParams {
             mcp_tools,
             deferred_mcp_tools,
-            discoverable_tools,
+            tool_suggest_candidates,
             extension_tool_executors: extension_tool_executors(sess),
             dynamic_tools: turn_context.dynamic_tools.as_slice(),
         },