preserve search results order in tool_search_output (#17263)

we used to alpha-sort tool search results because we were using
`BTreeMap`, which threw away the actual search result ordering.

Now we use a vec to preserve it.

### Tests
Updated tests

codex-rs/tools/src/tool_discovery.rs

@@ -204,16 +204,17 @@ pub fn create_tool_search_tool(
 pub fn collect_tool_search_output_tools<'a>(
     tool_sources: impl IntoIterator<Item = ToolSearchResultSource<'a>>,
 ) -> Result<Vec<ToolSearchOutputTool>, serde_json::Error> {
-    let grouped = tool_sources.into_iter().fold(
+    let mut grouped: Vec<(&'a str, Vec<ToolSearchResultSource<'a>>)> = Vec::new();
-        BTreeMap::<String, Vec<(String, ToolSearchResultSource<'a>)>>::new(),
+    for tool in tool_sources {
-        |mut grouped, tool| {
+        if let Some((_, tools)) = grouped
-            grouped
+            .iter_mut()
-                .entry(tool.tool_namespace.to_string())
+            .find(|(tool_namespace, _)| *tool_namespace == tool.tool_namespace)
-                .or_default()
+        {
-                .push((tool.tool_name.to_string(), tool));
+            tools.push(tool);
-            grouped
+        } else {
-        },
+            grouped.push((tool.tool_namespace, vec![tool]));
-    );
+        }
+    }
 
     let mut results = Vec::with_capacity(grouped.len());
     for (tool_namespace, tools) in grouped {
@@ -222,12 +223,10 @@ pub fn collect_tool_search_output_tools<'a>(
         };
 
         let description = first_tool
-            .1
             .connector_description
             .map(str::to_string)
             .or_else(|| {
                 first_tool
-                    .1
                     .connector_name
                     .map(str::trim)
                     .filter(|connector_name| !connector_name.is_empty())
@@ -236,14 +235,14 @@ pub fn collect_tool_search_output_tools<'a>(
             .or_else(|| {
                 Some(format!(
                     "Tools from the {} MCP server.",
-                    first_tool.1.server_name
+                    first_tool.server_name
                 ))
             });
 
         let tools = tools
             .iter()
             .map(|tool| {
-                mcp_tool_to_deferred_responses_api_tool(tool.0.clone(), tool.1.tool)
+                mcp_tool_to_deferred_responses_api_tool(tool.tool_name.to_string(), tool.tool)
                     .map(ResponsesApiNamespaceTool::Function)
             })
             .collect::<Result<Vec<_>, _>>()?;

codex-rs/tools/src/tool_discovery_tests.rs

@@ -137,13 +137,22 @@ fn create_tool_suggest_tool_uses_plugin_summary_fallback() {
 }
 
 #[test]
-fn collect_tool_search_output_tools_groups_results_by_namespace() {
+fn collect_tool_search_output_tools_preserves_search_order_while_grouping_by_namespace() {
     let calendar_create_event = mcp_tool("calendar-create-event", "Create a calendar event.");
     let gmail_read_email = mcp_tool("gmail-read-email", "Read an email.");
+    let gmail_send_email = mcp_tool("gmail-send-email", "Send an email.");
     let calendar_list_events = mcp_tool("calendar-list-events", "List calendar events.");
     let docs_search = mcp_tool("search", "Search docs.");
 
     let tools = collect_tool_search_output_tools([
+        ToolSearchResultSource {
+            server_name: "codex_apps",
+            tool_namespace: "mcp__codex_apps__gmail",
+            tool_name: "_send_email",
+            tool: &gmail_send_email,
+            connector_name: Some("Gmail"),
+            connector_description: Some("Read mail"),
+        },
         ToolSearchResultSource {
             server_name: "codex_apps",
             tool_namespace: "mcp__codex_apps__calendar",
@@ -182,6 +191,36 @@ fn collect_tool_search_output_tools_groups_results_by_namespace() {
     assert_eq!(
         tools,
         vec![
+            ToolSearchOutputTool::Namespace(ResponsesApiNamespace {
+                name: "mcp__codex_apps__gmail".to_string(),
+                description: "Read mail".to_string(),
+                tools: vec![
+                    ResponsesApiNamespaceTool::Function(ResponsesApiTool {
+                        name: "_send_email".to_string(),
+                        description: "Send an email.".to_string(),
+                        strict: false,
+                        defer_loading: Some(true),
+                        parameters: JsonSchema::object(
+                            Default::default(),
+                            /*required*/ None,
+                            /*additional_properties*/ None
+                        ),
+                        output_schema: None,
+                    }),
+                    ResponsesApiNamespaceTool::Function(ResponsesApiTool {
+                        name: "_read_email".to_string(),
+                        description: "Read an email.".to_string(),
+                        strict: false,
+                        defer_loading: Some(true),
+                        parameters: JsonSchema::object(
+                            Default::default(),
+                            /*required*/ None,
+                            /*additional_properties*/ None
+                        ),
+                        output_schema: None,
+                    }),
+                ],
+            }),
             ToolSearchOutputTool::Namespace(ResponsesApiNamespace {
                 name: "mcp__codex_apps__calendar".to_string(),
                 description: "Plan events".to_string(),
@@ -212,22 +251,6 @@ fn collect_tool_search_output_tools_groups_results_by_namespace() {
                     }),
                 ],
             }),
-            ToolSearchOutputTool::Namespace(ResponsesApiNamespace {
-                name: "mcp__codex_apps__gmail".to_string(),
-                description: "Read mail".to_string(),
-                tools: vec![ResponsesApiNamespaceTool::Function(ResponsesApiTool {
-                    name: "_read_email".to_string(),
-                    description: "Read an email.".to_string(),
-                    strict: false,
-                    defer_loading: Some(true),
-                    parameters: JsonSchema::object(
-                        Default::default(),
-                        /*required*/ None,
-                        /*additional_properties*/ None
-                    ),
-                    output_schema: None,
-                })],
-            }),
             ToolSearchOutputTool::Namespace(ResponsesApiNamespace {
                 name: "mcp__docs__".to_string(),
                 description: "Tools from the docs MCP server.".to_string(),