1- Add model service tiers metadata (#20969)

## Why

The model list needs to carry display-ready service tier metadata so
clients can render tier choices with stable IDs, names, and
descriptions. A raw speed-tier string list is not enough for richer UI
copy or future tier labels.

## What changed

- Added `ModelServiceTier` to shared model metadata with string `id`,
`name`, and `description` fields.
- Added `service_tiers` to `ModelInfo` and `ModelPreset`, preserving
empty defaults for older cached model payloads.
- Exposed `serviceTiers` on app-server v2 `Model` responses and threaded
it through TUI app-server model conversion.
- Marked legacy `additional_speed_tiers` / `additionalSpeedTiers`
metadata as deprecated in source and generated schema output.
- Regenerated app-server protocol JSON schema and TypeScript fixtures,
including `ModelServiceTier.ts`.

## Verification

- Ran `just write-app-server-schema`.
- Did not run local tests per repo instruction; relying on PR CI.

---------

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

codex-rs/protocol/src/openai_models.rs

@@ -115,6 +115,13 @@ pub struct ModelAvailabilityNux {
     pub message: String,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema, PartialEq, Eq)]
+pub struct ModelServiceTier {
+    pub id: String,
+    pub name: String,
+    pub description: String,
+}
+
 /// Metadata describing a Codex-supported model.
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema, PartialEq)]
 pub struct ModelPreset {
@@ -133,9 +140,12 @@ pub struct ModelPreset {
     /// Whether this model supports personality-specific instructions.
     #[serde(default)]
     pub supports_personality: bool,
-    /// Additional speed tiers this model can run with beyond the standard path.
+    /// Deprecated: use `service_tiers` instead.
     #[serde(default)]
     pub additional_speed_tiers: Vec<String>,
+    /// Service tiers this model can run with.
+    #[serde(default)]
+    pub service_tiers: Vec<ModelServiceTier>,
     /// Whether this is the default model for new users.
     pub is_default: bool,
     /// recommended upgrade model
@@ -258,6 +268,8 @@ pub struct ModelInfo {
     pub priority: i32,
     #[serde(default)]
     pub additional_speed_tiers: Vec<String>,
+    #[serde(default)]
+    pub service_tiers: Vec<ModelServiceTier>,
     pub availability_nux: Option<ModelAvailabilityNux>,
     pub upgrade: Option<ModelInfoUpgrade>,
     pub base_instructions: String,
@@ -442,6 +454,7 @@ impl From<ModelInfo> for ModelPreset {
             supported_reasoning_efforts: info.supported_reasoning_levels.clone(),
             supports_personality,
             additional_speed_tiers: info.additional_speed_tiers,
+            service_tiers: info.service_tiers,
             is_default: false, // default is the highest priority available model
             upgrade: info.upgrade.as_ref().map(|upgrade| ModelUpgrade {
                 id: upgrade.model.clone(),
@@ -464,9 +477,13 @@ impl From<ModelInfo> for ModelPreset {
 
 impl ModelPreset {
     pub fn supports_fast_mode(&self) -> bool {
-        self.additional_speed_tiers
+        self.service_tiers
             .iter()
-            .any(|tier| tier == SPEED_TIER_FAST)
+            .any(|tier| tier.id == SPEED_TIER_FAST)
+            || self
+                .additional_speed_tiers
+                .iter()
+                .any(|tier| tier == SPEED_TIER_FAST)
     }
 
     /// Filter models based on authentication mode.
@@ -548,6 +565,7 @@ mod tests {
             supported_in_api: true,
             priority: 1,
             additional_speed_tiers: Vec::new(),
+            service_tiers: Vec::new(),
             availability_nux: None,
             upgrade: None,
             base_instructions: "base".to_string(),
@@ -818,6 +836,7 @@ mod tests {
                 message: "Try Spark.".to_string(),
             }),
             additional_speed_tiers: vec![SPEED_TIER_FAST.to_string()],
+            service_tiers: Vec::new(),
             ..test_model(/*spec*/ None)
         });
 
@@ -829,4 +848,18 @@ mod tests {
         );
         assert!(preset.supports_fast_mode());
     }
+
+    #[test]
+    fn model_preset_supports_fast_mode_from_service_tiers() {
+        let preset = ModelPreset::from(ModelInfo {
+            service_tiers: vec![ModelServiceTier {
+                id: SPEED_TIER_FAST.to_string(),
+                name: "Fast".to_string(),
+                description: "Priority processing.".to_string(),
+            }],
+            ..test_model(/*spec*/ None)
+        });
+
+        assert!(preset.supports_fast_mode());
+    }
 }