Use model metadata for Fast Mode status (#16949)

Fast Mode status was still tied to one model name in the TUI and
model-list plumbing. This changes the model metadata shape so a model
can advertise additional speed tiers, carries that field through the
app-server model list, and uses it to decide when to show Fast Mode
status.

For people using Codex, the behavior is intended to stay the same for
existing models. Fast Mode still requires the existing signed-in /
feature-gated path; the difference is that the UI can now recognize any
model the model list marks as Fast-capable, instead of requiring a new
client-side slug check.

codex-rs/protocol/src/openai_models.rs

@@ -20,6 +20,7 @@ use crate::config_types::ReasoningSummary;
 use crate::config_types::Verbosity;
 
 const PERSONALITY_PLACEHOLDER: &str = "{{ personality }}";
+pub const SPEED_TIER_FAST: &str = "fast";
 
 /// See https://platform.openai.com/docs/guides/reasoning?api-mode=responses#get-started-with-reasoning
 #[derive(
@@ -132,6 +133,9 @@ 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.
+    #[serde(default)]
+    pub additional_speed_tiers: Vec<String>,
     /// Whether this is the default model for new users.
     pub is_default: bool,
     /// recommended upgrade model
@@ -252,6 +256,8 @@ pub struct ModelInfo {
     pub visibility: ModelVisibility,
     pub supported_in_api: bool,
     pub priority: i32,
+    #[serde(default)]
+    pub additional_speed_tiers: Vec<String>,
     pub availability_nux: Option<ModelAvailabilityNux>,
     pub upgrade: Option<ModelInfoUpgrade>,
     pub base_instructions: String,
@@ -428,6 +434,7 @@ impl From<ModelInfo> for ModelPreset {
                 .unwrap_or(ReasoningEffort::None),
             supported_reasoning_efforts: info.supported_reasoning_levels.clone(),
             supports_personality,
+            additional_speed_tiers: info.additional_speed_tiers,
             is_default: false, // default is the highest priority available model
             upgrade: info.upgrade.as_ref().map(|upgrade| ModelUpgrade {
                 id: upgrade.model.clone(),
@@ -449,6 +456,12 @@ impl From<ModelInfo> for ModelPreset {
 }
 
 impl ModelPreset {
+    pub fn supports_fast_mode(&self) -> bool {
+        self.additional_speed_tiers
+            .iter()
+            .any(|tier| tier == SPEED_TIER_FAST)
+    }
+
     /// Filter models based on authentication mode.
     ///
     /// In ChatGPT mode, all models are visible. Otherwise, only API-supported models are shown.
@@ -527,6 +540,7 @@ mod tests {
             visibility: ModelVisibility::List,
             supported_in_api: true,
             priority: 1,
+            additional_speed_tiers: Vec::new(),
             availability_nux: None,
             upgrade: None,
             base_instructions: "base".to_string(),
@@ -772,6 +786,7 @@ mod tests {
             availability_nux: Some(ModelAvailabilityNux {
                 message: "Try Spark.".to_string(),
             }),
+            additional_speed_tiers: vec![SPEED_TIER_FAST.to_string()],
             ..test_model(/*spec*/ None)
         });
 
@@ -781,5 +796,6 @@ mod tests {
                 message: "Try Spark.".to_string(),
             })
         );
+        assert!(preset.supports_fast_mode());
     }
 }