[codex] Require model for standalone web search (#25131)

## Why

The standalone `/v1/alpha/search` request now requires a `model`, but
the `web.run` extension currently omits it.

Adds `model` to extension `ToolCall` invocation.

Follow-up to #23823.

## What changed

- Make `SearchRequest.model` required.
- Expose the effective per-turn model on extension tool calls and pass
it in standalone web-search requests.
- Assert the model is forwarded in the app-server round-trip test.

## Testing

- `just test -p codex-api -p codex-tools -p codex-web-search-extension
-p codex-memories-extension -p codex-goal-extension`
- `just test -p codex-core -E
'test(passes_turn_fields_and_scoped_turn_item_emitter_to_extension_call)'`
- `just test -p codex-app-server -E
'test(standalone_web_search_round_trips_encrypted_output)'`

codex-rs/app-server/tests/suite/v2/web_search.rs

@@ -140,6 +140,7 @@ async fn standalone_web_search_round_trips_encrypted_output() -> Result<()> {
     );
 
     let search_body = search_request_body(&server).await?;
+    assert_eq!(search_body["model"], json!("mock-model"));
     assert_eq!(
         search_body["commands"],
         json!({

codex-rs/codex-api/src/endpoint/search.rs

@@ -145,7 +145,7 @@ mod tests {
             .search(
                 &SearchRequest {
                     id: "search-session".to_string(),
-                    model: Some("gpt-test".to_string()),
+                    model: "gpt-test".to_string(),
                     reasoning: None,
                     input: Some(SearchInput::Items(vec![ResponseItem::Message {
                         id: None,

codex-rs/codex-api/src/search.rs

@@ -7,8 +7,7 @@ use serde::Serialize;
 #[derive(Debug, Clone, Serialize, PartialEq)]
 pub struct SearchRequest {
     pub id: String,
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub model: Option<String>,
+    pub model: String,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub reasoning: Option<Reasoning>,
     #[serde(skip_serializing_if = "Option::is_none")]

codex-rs/core/src/tools/handlers/extension_tools.rs

@@ -147,6 +147,7 @@ async fn to_extension_call(invocation: &ToolInvocation) -> ExtensionToolCall {
         turn_id: invocation.turn.sub_id.clone(),
         call_id: invocation.call_id.clone(),
         tool_name: invocation.tool_name.clone(),
+        model: invocation.turn.model_info.slug.clone(),
         truncation_policy: invocation.turn.truncation_policy,
         conversation_history,
         turn_item_emitter: Arc::new(CoreTurnItemEmitter {
@@ -307,6 +308,7 @@ mod tests {
         let weak_session = Arc::downgrade(&session);
         let weak_turn = Arc::downgrade(&turn);
         let turn_id = turn.sub_id.clone();
+        let model = turn.model_info.slug.clone();
         let truncation_policy = turn.truncation_policy;
         let history_item = ResponseItem::Message {
             id: None,
@@ -350,6 +352,7 @@ mod tests {
             captured_call.tool_name,
             codex_tools::ToolName::plain("extension_echo")
         );
+        assert_eq!(captured_call.model, model);
         assert_eq!(captured_call.truncation_policy, truncation_policy);
         assert_eq!(
             captured_call.conversation_history.items(),

codex-rs/ext/goal/tests/goal_extension_backend.rs

@@ -1129,6 +1129,7 @@ fn tool_call(tool_name: &str, call_id: &str, arguments: serde_json::Value) -> To
         turn_id: "turn-1".to_string(),
         call_id: call_id.to_string(),
         tool_name: codex_extension_api::ToolName::plain(tool_name),
+        model: "gpt-test".to_string(),
         truncation_policy: TruncationPolicy::Bytes(1024),
         conversation_history: codex_extension_api::ConversationHistory::default(),
         turn_item_emitter: Arc::new(NoopTurnItemEmitter),

codex-rs/ext/memories/src/tests.rs

@@ -211,6 +211,7 @@ async fn add_ad_hoc_note_tool_creates_note_file() {
             turn_id: "turn-1".to_string(),
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::ADD_AD_HOC_NOTE_TOOL_NAME),
+            model: "gpt-test".to_string(),
             truncation_policy: TruncationPolicy::Bytes(1024),
             conversation_history: codex_extension_api::ConversationHistory::default(),
             turn_item_emitter: Arc::new(NoopTurnItemEmitter),
@@ -253,6 +254,7 @@ async fn add_ad_hoc_note_tool_rejects_paths_as_filenames() {
             turn_id: "turn-1".to_string(),
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::ADD_AD_HOC_NOTE_TOOL_NAME),
+            model: "gpt-test".to_string(),
             truncation_policy: TruncationPolicy::Bytes(1024),
             conversation_history: codex_extension_api::ConversationHistory::default(),
             turn_item_emitter: Arc::new(NoopTurnItemEmitter),
@@ -296,6 +298,7 @@ async fn read_tool_reads_memory_file() {
             turn_id: "turn-1".to_string(),
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::READ_TOOL_NAME),
+            model: "gpt-test".to_string(),
             truncation_policy: TruncationPolicy::Bytes(1024),
             conversation_history: codex_extension_api::ConversationHistory::default(),
             turn_item_emitter: Arc::new(NoopTurnItemEmitter),
@@ -342,6 +345,7 @@ async fn search_tool_accepts_multiple_queries() {
             turn_id: "turn-1".to_string(),
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::SEARCH_TOOL_NAME),
+            model: "gpt-test".to_string(),
             truncation_policy: TruncationPolicy::Bytes(1024),
             conversation_history: codex_extension_api::ConversationHistory::default(),
             turn_item_emitter: Arc::new(NoopTurnItemEmitter),
@@ -414,6 +418,7 @@ async fn search_tool_accepts_windowed_all_match_mode() {
             turn_id: "turn-1".to_string(),
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::SEARCH_TOOL_NAME),
+            model: "gpt-test".to_string(),
             truncation_policy: TruncationPolicy::Bytes(1024),
             conversation_history: codex_extension_api::ConversationHistory::default(),
             turn_item_emitter: Arc::new(NoopTurnItemEmitter),
@@ -466,6 +471,7 @@ async fn search_tool_rejects_legacy_single_query() {
             turn_id: "turn-1".to_string(),
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::SEARCH_TOOL_NAME),
+            model: "gpt-test".to_string(),
             truncation_policy: TruncationPolicy::Bytes(1024),
             conversation_history: codex_extension_api::ConversationHistory::default(),
             turn_item_emitter: Arc::new(NoopTurnItemEmitter),

codex-rs/ext/web-search/src/tool.rs

@@ -90,7 +90,7 @@ impl ToolExecutor<ToolCall> for WebSearchTool {
         );
         let request = SearchRequest {
             id: self.session_id.clone(),
-            model: None,
+            model: call.model.clone(),
             reasoning: None,
             input: recent_input(call.conversation_history.items()),
             commands: Some(commands),

codex-rs/tools/src/tool_call.rs

@@ -87,6 +87,7 @@ pub struct ToolCall {
     pub turn_id: String,
     pub call_id: String,
     pub tool_name: ToolName,
+    pub model: String,
     pub truncation_policy: TruncationPolicy,
     pub conversation_history: ConversationHistory,
     pub turn_item_emitter: Arc<dyn TurnItemEmitter>,
@@ -99,6 +100,7 @@ impl std::fmt::Debug for ToolCall {
             .field("turn_id", &self.turn_id)
             .field("call_id", &self.call_id)
             .field("tool_name", &self.tool_name)
+            .field("model", &self.model)
             .field("truncation_policy", &self.truncation_policy)
             .field("conversation_history", &self.conversation_history)
             .field("turn_item_emitter", &"<host turn item emitter>")