[codex] Treat max as a first-class reasoning effort (#30467)

## Why

The Bedrock GPT-5.6 catalog advertises `max`, but Codex treated it as an
opaque custom effort. That made the reasoning picker render it as
lowercase `max` while known efforts use productized labels.

Making `max` a known effort aligns catalog data, parsing, and UI
presentation without changing the `max` wire value or persisted
representation.

## What changed

- Add first-class `ReasoningEffort::Max` parsing and serialization.
- Use the typed effort in the Bedrock catalog and render it as `Max` in
the TUI.
- Preserve forward-compatible custom-effort coverage with a genuinely
unknown `future` value.

### Before
<img width="559" height="124" alt="Screenshot 2026-06-28 at 12 08 47 PM"
src="https://github.com/user-attachments/assets/7c43cf4f-020b-4605-9239-0a9c97eb7364"
/>

### After
<img width="558" height="107" alt="Screenshot 2026-06-28 at 12 09 10 PM"
src="https://github.com/user-attachments/assets/b9cc5ded-c940-43b4-b024-bba25abe0a17"
/>

codex-rs/core/src/client.rs

@@ -169,7 +169,7 @@ pub(crate) struct CompactConversationRequestSettings {
 
 fn reasoning_effort_for_request(effort: ReasoningEffortConfig) -> ReasoningEffortConfig {
     match effort {
-        ReasoningEffortConfig::Ultra => ReasoningEffortConfig::Custom("max".to_string()),
+        ReasoningEffortConfig::Ultra => ReasoningEffortConfig::Max,
         effort => effort,
     }
 }

codex-rs/core/src/client_tests.rs

@@ -292,10 +292,7 @@ fn ultra_reasoning_uses_max_for_requests() {
             super::reasoning_effort_for_request(ReasoningEffort::Ultra),
             super::reasoning_effort_for_request(ReasoningEffort::High),
         ),
-        (
-            ReasoningEffort::Custom("max".to_string()),
-            ReasoningEffort::High,
-        )
+        (ReasoningEffort::Max, ReasoningEffort::High,)
     );
 }
 

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

@@ -2171,7 +2171,7 @@ async fn skills_use_aliases_in_developer_message_under_budget_pressure() {
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn includes_configured_effort_in_request() -> anyhow::Result<()> {
+async fn includes_configured_max_effort_in_request() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
     let server = MockServer::start().await;
 
@@ -2183,7 +2183,7 @@ async fn includes_configured_effort_in_request() -> anyhow::Result<()> {
     let TestCodex { codex, .. } = test_codex()
         .with_model("gpt-5.4")
         .with_config(|config| {
-            config.model_reasoning_effort = Some(ReasoningEffort::Medium);
+            config.model_reasoning_effort = Some(ReasoningEffort::Max);
         })
         .build(&server)
         .await?;
@@ -2212,7 +2212,7 @@ async fn includes_configured_effort_in_request() -> anyhow::Result<()> {
             .get("reasoning")
             .and_then(|t| t.get("effort"))
             .and_then(|v| v.as_str()),
-        Some("medium")
+        Some("max")
     );
 
     Ok(())

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

@@ -329,7 +329,7 @@ async fn remote_models_long_model_slug_is_sent_with_custom_reasoning() -> Result
         /*priority*/ 1_000,
         TruncationPolicyConfig::bytes(/*limit*/ 10_000),
     );
-    let custom_reasoning_effort = ReasoningEffort::Custom("max".to_string());
+    let custom_reasoning_effort = ReasoningEffort::Custom("future".to_string());
     remote_model.default_reasoning_level = Some(custom_reasoning_effort.clone());
     remote_model.supported_reasoning_levels = vec![
         ReasoningEffortPreset {
@@ -391,7 +391,7 @@ async fn remote_models_long_model_slug_is_sent_with_custom_reasoning() -> Result
         .and_then(|reasoning| reasoning.get("summary"))
         .and_then(|value| value.as_str());
     assert_eq!(body["model"].as_str(), Some(requested_model));
-    assert_eq!(reasoning_effort, Some("max"));
+    assert_eq!(reasoning_effort, Some("future"));
     assert_eq!(reasoning_summary, Some("detailed"));
 
     Ok(())

codex-rs/model-provider/src/amazon_bedrock/catalog.rs

@@ -70,7 +70,7 @@ fn gpt_5_6_bedrock_model(bedrock_slug: &str, display_name: &str, priority: i32)
     model
         .supported_reasoning_levels
         .push(ReasoningEffortPreset {
-            effort: ReasoningEffort::Custom("max".to_string()),
+            effort: ReasoningEffort::Max,
             description: "Maximum reasoning depth for the hardest problems".to_string(),
         });
     model
@@ -148,7 +148,7 @@ mod tests {
             expected
                 .supported_reasoning_levels
                 .push(ReasoningEffortPreset {
-                    effort: ReasoningEffort::Custom("max".to_string()),
+                    effort: ReasoningEffort::Max,
                     description: "Maximum reasoning depth for the hardest problems".to_string(),
                 });
 

codex-rs/protocol/src/openai_models.rs

@@ -45,6 +45,7 @@ pub enum ReasoningEffort {
     Medium,
     High,
     XHigh,
+    Max,
     Ultra,
     /// A model-defined effort value that this client does not know yet.
     Custom(String),
@@ -60,6 +61,7 @@ impl ReasoningEffort {
             Self::Medium => "medium",
             Self::High => "high",
             Self::XHigh => "xhigh",
+            Self::Max => "max",
             Self::Ultra => "ultra",
             Self::Custom(effort) => effort,
         }
@@ -125,6 +127,7 @@ impl FromStr for ReasoningEffort {
             "medium" => Ok(Self::Medium),
             "high" => Ok(Self::High),
             "xhigh" => Ok(Self::XHigh),
+            "max" => Ok(Self::Max),
             "ultra" => Ok(Self::Ultra),
             "" => Err("reasoning_effort must not be empty".to_string()),
             effort => Ok(Self::Custom(effort.to_string())),
@@ -703,30 +706,35 @@ mod tests {
 
     #[test]
     fn reasoning_effort_accepts_known_and_custom_values() {
-        let custom = ReasoningEffort::Custom("max".to_string());
-        let deserialized = from_str::<ReasoningEffort>(r#""max""#)
+        let custom = ReasoningEffort::Custom("future".to_string());
+        let deserialized = from_str::<ReasoningEffort>(r#""future""#)
             .expect("custom reasoning effort should deserialize");
         let serialized = to_string(&custom).expect("custom reasoning effort should serialize");
+        let serialized_max = to_string(&ReasoningEffort::Max).expect("Max should serialize");
         let serialized_ultra = to_string(&ReasoningEffort::Ultra).expect("Ultra should serialize");
 
         assert_eq!(
             (
                 "high".parse(),
-                "ultra".parse(),
                 "max".parse(),
+                "ultra".parse(),
+                "future".parse(),
                 deserialized,
                 serialized,
+                serialized_max,
                 serialized_ultra,
                 custom.to_string(),
             ),
             (
                 Ok(ReasoningEffort::High),
+                Ok(ReasoningEffort::Max),
                 Ok(ReasoningEffort::Ultra),
                 Ok(custom.clone()),
                 custom,
+                r#""future""#.to_string(),
                 r#""max""#.to_string(),
                 r#""ultra""#.to_string(),
-                "max".to_string(),
+                "future".to_string(),
             )
         );
     }

codex-rs/tui/src/chatwidget/model_popups.rs

@@ -505,6 +505,7 @@ impl ChatWidget {
             ReasoningEffortConfig::Medium => "Medium".to_string(),
             ReasoningEffortConfig::High => "High".to_string(),
             ReasoningEffortConfig::XHigh => "Extra high".to_string(),
+            ReasoningEffortConfig::Max => "Max".to_string(),
             ReasoningEffortConfig::Ultra => "Ultra".to_string(),
             ReasoningEffortConfig::Custom(value) => value.clone(),
         }

codex-rs/tui/src/chatwidget/reasoning_shortcuts.rs

@@ -225,7 +225,7 @@ mod tests {
 
     #[test]
     fn next_reasoning_effort_uses_advertised_order_for_custom_levels() {
-        let custom_effort = ReasoningEffortConfig::Custom("max".to_string());
+        let custom_effort = ReasoningEffortConfig::Custom("future".to_string());
         let choices = vec![
             ReasoningEffortConfig::High,
             ReasoningEffortConfig::Low,

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__model_reasoning_selection_popup.snap

@@ -6,7 +6,7 @@ expression: popup
 
   1. Low               Fast responses with lighter reasoning
   2. Medium (default)  Balances speed and reasoning depth for everyday tasks
-  3. max               Maximum available reasoning
+  3. Max               Maximum available reasoning
 › 4. High (current)    Greater reasoning depth for complex problems
   5. Extra high        Extra high reasoning depth for complex problems
 

codex-rs/tui/src/chatwidget/tests/popups_and_settings.rs

@@ -3191,7 +3191,7 @@ async fn model_reasoning_selection_popup_snapshot() {
     preset.supported_reasoning_efforts.insert(
         2,
         ReasoningEffortPreset {
-            effort: ReasoningEffortConfig::Custom("max".to_string()),
+            effort: ReasoningEffortConfig::Max,
             description: "Maximum available reasoning".to_string(),
         },
     );
@@ -3204,7 +3204,7 @@ async fn model_reasoning_selection_popup_snapshot() {
 #[tokio::test]
 async fn model_reasoning_selection_popup_applies_custom_effort() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.4")).await;
-    let custom_effort = ReasoningEffortConfig::Custom("max".to_string());
+    let custom_effort = ReasoningEffortConfig::Custom("future".to_string());
     chat.set_reasoning_effort(Some(ReasoningEffortConfig::XHigh));
 
     let mut preset = get_available_model(&chat, "gpt-5.4");