[app-server] model/list API (#5382)

Adds a `model/list` paginated API that returns the list of models
supported by Codex.

codex-rs/common/src/model_presets.rs

@@ -1,73 +1,96 @@
 use codex_app_server_protocol::AuthMode;
 use codex_core::protocol_config_types::ReasoningEffort;
 
-/// A simple preset pairing a model slug with a reasoning effort.
+/// A reasoning effort option that can be surfaced for a model.
+#[derive(Debug, Clone, Copy)]
+pub struct ReasoningEffortPreset {
+    /// Effort level that the model supports.
+    pub effort: ReasoningEffort,
+    /// Short human description shown next to the effort in UIs.
+    pub description: &'static str,
+}
+
+/// Metadata describing a Codex-supported model.
 #[derive(Debug, Clone, Copy)]
 pub struct ModelPreset {
     /// Stable identifier for the preset.
     pub id: &'static str,
-    /// Display label shown in UIs.
-    pub label: &'static str,
-    /// Short human description shown next to the label in UIs.
-    pub description: &'static str,
     /// Model slug (e.g., "gpt-5").
     pub model: &'static str,
-    /// Reasoning effort to apply for this preset.
-    pub effort: Option<ReasoningEffort>,
+    /// Display name shown in UIs.
+    pub display_name: &'static str,
+    /// Short human description shown in UIs.
+    pub description: &'static str,
+    /// Reasoning effort applied when none is explicitly chosen.
+    pub default_reasoning_effort: ReasoningEffort,
+    /// Supported reasoning effort options.
+    pub supported_reasoning_efforts: &'static [ReasoningEffortPreset],
+    /// Whether this is the default model for new users.
+    pub is_default: bool,
 }
 
 const PRESETS: &[ModelPreset] = &[
     ModelPreset {
-        id: "gpt-5-codex-low",
-        label: "gpt-5-codex low",
-        description: "Fastest responses with limited reasoning",
+        id: "gpt-5-codex",
         model: "gpt-5-codex",
-        effort: Some(ReasoningEffort::Low),
+        display_name: "gpt-5-codex",
+        description: "Optimized for coding tasks with many tools.",
+        default_reasoning_effort: ReasoningEffort::Medium,
+        supported_reasoning_efforts: &[
+            ReasoningEffortPreset {
+                effort: ReasoningEffort::Low,
+                description: "Fastest responses with limited reasoning",
+            },
+            ReasoningEffortPreset {
+                effort: ReasoningEffort::Medium,
+                description: "Dynamically adjusts reasoning based on the task",
+            },
+            ReasoningEffortPreset {
+                effort: ReasoningEffort::High,
+                description: "Maximizes reasoning depth for complex or ambiguous problems",
+            },
+        ],
+        is_default: true,
     },
     ModelPreset {
-        id: "gpt-5-codex-medium",
-        label: "gpt-5-codex medium",
-        description: "Dynamically adjusts reasoning based on the task",
-        model: "gpt-5-codex",
-        effort: Some(ReasoningEffort::Medium),
-    },
-    ModelPreset {
-        id: "gpt-5-codex-high",
-        label: "gpt-5-codex high",
-        description: "Maximizes reasoning depth for complex or ambiguous problems",
-        model: "gpt-5-codex",
-        effort: Some(ReasoningEffort::High),
-    },
-    ModelPreset {
-        id: "gpt-5-minimal",
-        label: "gpt-5 minimal",
-        description: "Fastest responses with little reasoning",
+        id: "gpt-5",
         model: "gpt-5",
-        effort: Some(ReasoningEffort::Minimal),
-    },
-    ModelPreset {
-        id: "gpt-5-low",
-        label: "gpt-5 low",
-        description: "Balances speed with some reasoning; useful for straightforward queries and short explanations",
-        model: "gpt-5",
-        effort: Some(ReasoningEffort::Low),
-    },
-    ModelPreset {
-        id: "gpt-5-medium",
-        label: "gpt-5 medium",
-        description: "Provides a solid balance of reasoning depth and latency for general-purpose tasks",
-        model: "gpt-5",
-        effort: Some(ReasoningEffort::Medium),
-    },
-    ModelPreset {
-        id: "gpt-5-high",
-        label: "gpt-5 high",
-        description: "Maximizes reasoning depth for complex or ambiguous problems",
-        model: "gpt-5",
-        effort: Some(ReasoningEffort::High),
+        display_name: "gpt-5",
+        description: "Broad world knowledge with strong general reasoning.",
+        default_reasoning_effort: ReasoningEffort::Medium,
+        supported_reasoning_efforts: &[
+            ReasoningEffortPreset {
+                effort: ReasoningEffort::Minimal,
+                description: "Fastest responses with little reasoning",
+            },
+            ReasoningEffortPreset {
+                effort: ReasoningEffort::Low,
+                description: "Balances speed with some reasoning; useful for straightforward queries and short explanations",
+            },
+            ReasoningEffortPreset {
+                effort: ReasoningEffort::Medium,
+                description: "Provides a solid balance of reasoning depth and latency for general-purpose tasks",
+            },
+            ReasoningEffortPreset {
+                effort: ReasoningEffort::High,
+                description: "Maximizes reasoning depth for complex or ambiguous problems",
+            },
+        ],
+        is_default: false,
     },
 ];
 
 pub fn builtin_model_presets(_auth_mode: Option<AuthMode>) -> Vec<ModelPreset> {
     PRESETS.to_vec()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn only_one_default_model_is_configured() {
+        let default_models = PRESETS.iter().filter(|preset| preset.is_default).count();
+        assert!(default_models == 1);
+    }
+}