Use model catalog default for reasoning summary fallback (#12873)

## Summary
- make `Config.model_reasoning_summary` optional so unset means use
model default
- resolve the optional config value to a concrete summary when building
`TurnContext`
- add protocol support for `default_reasoning_summary` in model metadata

## Validation
- `cargo test -p codex-core --lib client::tests -- --nocapture`

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/tests/suite/client.rs

@@ -31,6 +31,7 @@ use codex_protocol::models::ReasoningItemContent;
 use codex_protocol::models::ReasoningItemReasoningSummary;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::models::WebSearchAction;
+use codex_protocol::openai_models::ModelsResponse;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::Op;
@@ -980,7 +981,9 @@ async fn user_turn_collaboration_mode_overrides_model_and_effort() -> anyhow::Re
             sandbox_policy: config.permissions.sandbox_policy.get().clone(),
             model: session_configured.model.clone(),
             effort: Some(ReasoningEffort::Low),
-            summary: config.model_reasoning_summary,
+            summary: config
+                .model_reasoning_summary
+                .unwrap_or(ReasoningSummary::Auto),
             collaboration_mode: Some(collaboration_mode),
             final_output_json_schema: None,
             personality: None,
@@ -1014,7 +1017,7 @@ async fn configured_reasoning_summary_is_sent() -> anyhow::Result<()> {
     .await;
     let TestCodex { codex, .. } = test_codex()
         .with_config(|config| {
-            config.model_reasoning_summary = ReasoningSummary::Concise;
+            config.model_reasoning_summary = Some(ReasoningSummary::Concise);
         })
         .build(&server)
         .await?;
@@ -1058,7 +1061,7 @@ async fn reasoning_summary_is_omitted_when_disabled() -> anyhow::Result<()> {
     .await;
     let TestCodex { codex, .. } = test_codex()
         .with_config(|config| {
-            config.model_reasoning_summary = ReasoningSummary::None;
+            config.model_reasoning_summary = Some(ReasoningSummary::None);
         })
         .build(&server)
         .await?;
@@ -1089,6 +1092,60 @@ async fn reasoning_summary_is_omitted_when_disabled() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn reasoning_summary_none_overrides_model_catalog_default() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+    let server = MockServer::start().await;
+
+    let resp_mock = mount_sse_once(
+        &server,
+        sse(vec![ev_response_created("resp1"), ev_completed("resp1")]),
+    )
+    .await;
+
+    let mut model_catalog: ModelsResponse =
+        serde_json::from_str(include_str!("../../models.json")).expect("valid models.json");
+    let model = model_catalog
+        .models
+        .iter_mut()
+        .find(|model| model.slug == "gpt-5.1")
+        .expect("gpt-5.1 exists in bundled models.json");
+    model.supports_reasoning_summaries = true;
+    model.default_reasoning_summary = ReasoningSummary::Detailed;
+
+    let TestCodex { codex, .. } = test_codex()
+        .with_model("gpt-5.1")
+        .with_config(move |config| {
+            config.model_reasoning_summary = Some(ReasoningSummary::None);
+            config.model_catalog = Some(model_catalog);
+        })
+        .build(&server)
+        .await?;
+
+    codex
+        .submit(Op::UserInput {
+            items: vec![UserInput::Text {
+                text: "hello".into(),
+                text_elements: Vec::new(),
+            }],
+            final_output_json_schema: None,
+        })
+        .await
+        .unwrap();
+
+    wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
+
+    let request_body = resp_mock.single_request().body_json();
+    pretty_assertions::assert_eq!(
+        request_body
+            .get("reasoning")
+            .and_then(|reasoning| reasoning.get("summary")),
+        None
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn includes_default_verbosity_in_request() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
@@ -1441,7 +1498,14 @@ async fn azure_responses_request_includes_store_and_reasoning_ids() {
     });
 
     let mut stream = client_session
-        .stream(&prompt, &model_info, &otel_manager, effort, summary, None)
+        .stream(
+            &prompt,
+            &model_info,
+            &otel_manager,
+            effort,
+            summary.unwrap_or(ReasoningSummary::Auto),
+            None,
+        )
         .await
         .expect("responses stream to start");
 

codex-rs/core/tests/suite/collaboration_instructions.rs

@@ -169,7 +169,10 @@ async fn collaboration_instructions_added_on_user_turn() -> Result<()> {
             sandbox_policy: test.config.permissions.sandbox_policy.get().clone(),
             model: test.session_configured.model.clone(),
             effort: None,
-            summary: test.config.model_reasoning_summary,
+            summary: test
+                .config
+                .model_reasoning_summary
+                .unwrap_or(codex_protocol::config_types::ReasoningSummary::Auto),
             collaboration_mode: Some(collaboration_mode),
             final_output_json_schema: None,
             personality: None,
@@ -275,7 +278,10 @@ async fn user_turn_overrides_collaboration_instructions_after_override() -> Resu
             sandbox_policy: test.config.permissions.sandbox_policy.get().clone(),
             model: test.session_configured.model.clone(),
             effort: None,
-            summary: test.config.model_reasoning_summary,
+            summary: test
+                .config
+                .model_reasoning_summary
+                .unwrap_or(codex_protocol::config_types::ReasoningSummary::Auto),
             collaboration_mode: Some(turn_mode),
             final_output_json_schema: None,
             personality: None,

codex-rs/core/tests/suite/model_switching.rs

@@ -234,6 +234,7 @@ async fn model_change_from_image_to_text_strips_prior_image_content() -> Result<
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,
@@ -391,6 +392,7 @@ async fn model_switch_to_smaller_model_updates_token_context_window() -> Result<
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,

codex-rs/core/tests/suite/models_cache_ttl.rs

@@ -336,6 +336,7 @@ fn test_remote_model(slug: &str, priority: i32) -> ModelInfo {
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,

codex-rs/core/tests/suite/personality.rs

@@ -599,6 +599,7 @@ async fn remote_model_friendly_personality_instructions_with_feature() -> anyhow
             }),
         }),
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,
@@ -706,6 +707,7 @@ async fn user_turn_personality_remote_model_template_includes_update_message() -
             }),
         }),
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,

codex-rs/core/tests/suite/prompt_caching.rs

@@ -761,7 +761,7 @@ async fn send_user_turn_with_no_changes_does_not_send_environment_context() -> a
             sandbox_policy: default_sandbox_policy.clone(),
             model: default_model.clone(),
             effort: default_effort,
-            summary: default_summary,
+            summary: default_summary.unwrap_or(ReasoningSummary::Auto),
             collaboration_mode: None,
             final_output_json_schema: None,
             personality: None,
@@ -780,7 +780,7 @@ async fn send_user_turn_with_no_changes_does_not_send_environment_context() -> a
             sandbox_policy: default_sandbox_policy.clone(),
             model: default_model.clone(),
             effort: default_effort,
-            summary: default_summary,
+            summary: default_summary.unwrap_or(ReasoningSummary::Auto),
             collaboration_mode: None,
             final_output_json_schema: None,
             personality: None,
@@ -875,7 +875,7 @@ async fn send_user_turn_with_changes_sends_environment_context() -> anyhow::Resu
             sandbox_policy: default_sandbox_policy.clone(),
             model: default_model,
             effort: default_effort,
-            summary: default_summary,
+            summary: default_summary.unwrap_or(ReasoningSummary::Auto),
             collaboration_mode: None,
             final_output_json_schema: None,
             personality: None,

codex-rs/core/tests/suite/remote_models.rs

@@ -175,7 +175,9 @@ async fn remote_models_long_model_slug_is_sent_with_high_reasoning() -> Result<(
             sandbox_policy: config.permissions.sandbox_policy.get().clone(),
             model: requested_model.to_string(),
             effort: None,
-            summary: config.model_reasoning_summary,
+            summary: config
+                .model_reasoning_summary
+                .unwrap_or(ReasoningSummary::Auto),
             collaboration_mode: None,
             personality: None,
         })
@@ -227,7 +229,9 @@ async fn namespaced_model_slug_uses_catalog_metadata_without_fallback_warning()
             sandbox_policy: config.permissions.sandbox_policy.get().clone(),
             model: requested_model.to_string(),
             effort: None,
-            summary: config.model_reasoning_summary,
+            summary: config
+                .model_reasoning_summary
+                .unwrap_or(ReasoningSummary::Auto),
             collaboration_mode: None,
             personality: None,
         })
@@ -284,6 +288,7 @@ async fn remote_models_remote_model_uses_unified_exec() -> Result<()> {
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,
@@ -520,6 +525,7 @@ async fn remote_models_apply_remote_base_instructions() -> Result<()> {
         base_instructions: remote_base.to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,
@@ -980,6 +986,7 @@ fn test_remote_model_with_policy(
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,

codex-rs/core/tests/suite/resume_warning.rs

@@ -4,6 +4,7 @@ use codex_core::CodexAuth;
 use codex_core::NewThread;
 use codex_protocol::ThreadId;
 use codex_protocol::config_types::ModeKind;
+use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::InitialHistory;
 use codex_protocol::protocol::ResumedHistory;
@@ -34,7 +35,9 @@ fn resume_history(
         personality: None,
         collaboration_mode: None,
         effort: config.model_reasoning_effort,
-        summary: config.model_reasoning_summary,
+        summary: config
+            .model_reasoning_summary
+            .unwrap_or(ReasoningSummary::Auto),
         user_instructions: None,
         developer_instructions: None,
         final_output_json_schema: None,

codex-rs/core/tests/suite/rmcp_client.rs

@@ -398,6 +398,7 @@ async fn stdio_image_responses_are_sanitized_for_text_only_model() -> anyhow::Re
                 base_instructions: "base instructions".to_string(),
                 model_messages: None,
                 supports_reasoning_summaries: false,
+                default_reasoning_summary: ReasoningSummary::Auto,
                 support_verbosity: false,
                 default_verbosity: None,
                 apply_patch_tool_type: None,

codex-rs/core/tests/suite/view_image.rs

@@ -675,6 +675,7 @@ async fn view_image_tool_returns_unsupported_message_for_text_only_model() -> an
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,