Preserve Apps usage instructions in model catalog messages (#58441)

## What changed

Add optional `ModelMessages.apps` and `AppsMessages.usage_instructions` fields to carry model catalog wording without runtime interpretation. Missing or null values become `None`, and strings retain their exact contents, including empty strings, whitespace, and template-like text.

## Testing

Add serialization coverage for nullable and literal Apps values, and extend existing tests to verify Apps messages survive model response round trips and base instruction overrides.

GitOrigin-RevId: 49b516656255e07b91f8f4679e2acb8e1b03f9e1

codex-rs/app-server/tests/common/models_cache.rs

@@ -31,6 +31,7 @@ fn preset_to_info(preset: &ModelPreset, priority: i32) -> ModelInfo {
         available_access_programs: preset.available_access_programs.clone(),
         upgrade: preset.upgrade.as_ref().map(Into::into),
         model_messages: Some(ModelMessages {
+            apps: None,
             content_filter_guidance: None,
             persistent_instructions: None,
             tools: None,

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

@@ -40,6 +40,7 @@ async fn catalog_permission_message_loaded_from_remote_models_is_sent(
     let model_slug = "remote-catalog-permissions-model";
     let mut model = model_info_from_slug(model_slug);
     model.model_messages = Some(ModelMessages {
+        apps: None,
         content_filter_guidance: None,
         persistent_instructions: None,
         tools: None,

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

@@ -74,6 +74,7 @@ fn model_with_collaboration_messages(
 ) -> codex_protocol::openai_models::ModelInfo {
     let mut model = model_info_from_slug(slug);
     let model_messages = model.model_messages.get_or_insert(ModelMessages {
+        apps: None,
         content_filter_guidance: None,
         persistent_instructions: None,
         tools: None,

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

@@ -643,6 +643,7 @@ fn test_remote_model(slug: &str, priority: i32) -> ModelInfo {
         available_access_programs: None,
         upgrade: None,
         model_messages: Some(ModelMessages {
+            apps: None,
             content_filter_guidance: None,
             persistent_instructions: None,
             tools: None,

codex-rs/models-manager/src/model_info_tests.rs

@@ -3,6 +3,7 @@ use crate::ModelsManagerConfig;
 use codex_prompts::render_model_instructions;
 use codex_protocol::config_types::Personality;
 use codex_protocol::openai_models::ApprovalMessages;
+use codex_protocol::openai_models::AppsMessages;
 use codex_protocol::openai_models::AutoReviewMessages;
 use codex_protocol::openai_models::CollaborationModeMessages;
 use codex_protocol::openai_models::ConfirmationPolicies;
@@ -90,6 +91,9 @@ fn base_instruction_override_is_literal_and_preserves_catalog_messages() {
         computer_use: Some("  # Native policy\r\n\n${native_markdown}\n".to_string()),
     };
     let mut messages = ModelMessages {
+        apps: Some(AppsMessages {
+            usage_instructions: Some("Catalog Apps instructions.".to_string()),
+        }),
         content_filter_guidance: None,
         persistent_instructions: Some(persistent_instructions.to_string()),
         tools: Some(ToolMessages {

codex-rs/protocol/src/openai_models.rs

@@ -580,6 +580,9 @@ impl ModelInfo {
 /// retained for model catalog compatibility.
 #[derive(Debug, Default, Serialize, Deserialize, Clone, PartialEq, Eq, TS, JsonSchema)]
 pub struct ModelMessages {
+    /// Optional model-owned Apps wording, transported without runtime interpretation.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub apps: Option<AppsMessages>,
     /// Developer guidance after a content-filter block. Missing, null, blank, or values over
     /// 512 UTF-8 bytes use the bundled guidance.
     #[serde(default, skip_serializing_if = "Option::is_none")]
@@ -605,6 +608,15 @@ pub struct ModelMessages {
     pub confirmation_policies: Option<ConfirmationPolicies>,
 }
 
+/// Optional Apps wording from the model catalog, preserved for future runtime consumption.
+#[derive(Debug, Default, Serialize, Deserialize, Clone, PartialEq, Eq, TS, JsonSchema)]
+pub struct AppsMessages {
+    /// Missing and null deserialize as `None`; all strings preserve their exact bytes.
+    /// Rendering, size limits, and empty-string behavior are defined by consumers.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub usage_instructions: Option<String>,
+}
+
 /// Model-owned confirmation-policy Markdown, forwarded unchanged to actor tools.
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq, TS, JsonSchema)]
 pub struct ConfirmationPolicies {
@@ -1225,6 +1237,32 @@ mod tests {
         assert_eq!(messages, ModelMessages::default());
     }
 
+    #[test]
+    fn apps_messages_preserve_nullable_and_literal_wire_values() {
+        for apps in [
+            serde_json::Value::Null,
+            serde_json::json!({}),
+            serde_json::json!({"usage_instructions": null}),
+            serde_json::json!({"usage_instructions": ""}),
+            serde_json::json!({"usage_instructions": " \r\n\t"}),
+            serde_json::json!({"usage_instructions": "  {{literal}}\r\n"}),
+            serde_json::json!({"usage_instructions": "é".repeat(501)}),
+        ] {
+            let messages: ModelMessages =
+                serde_json::from_value(serde_json::json!({"apps": apps})).unwrap();
+            let serialized = serde_json::to_value(messages).unwrap();
+            let mut expected = serde_json::to_value(ModelMessages::default()).unwrap();
+            if !apps.is_null() {
+                expected["apps"] = if apps["usage_instructions"].is_null() {
+                    serde_json::json!({})
+                } else {
+                    apps
+                };
+            }
+            assert_eq!(serialized, expected);
+        }
+    }
+
     #[test]
     fn send_user_message_async_description_preserves_missing_null_and_empty_values() {
         for (value, expected) in [
@@ -1723,6 +1761,9 @@ mod tests {
     #[test]
     fn models_response_prefers_template_and_preserves_message_siblings() {
         let messages = ModelMessages {
+            apps: Some(AppsMessages {
+                usage_instructions: Some("Literal Apps {{guidance}}".to_string()),
+            }),
             content_filter_guidance: Some("Offer a permitted alternative.".to_string()),
             persistent_instructions: Some("Persistent catalog instructions".to_string()),
             tools: Some(ToolMessages {