Add model provider discovery to the app server (#58845)

## What changed

- Add `modelProvider/list` to return OpenAI and explicitly configured providers, provider-specific settings, and the selected default provider.
- Report `canEdit` and `canChangeDefault` based on configuration requirements, layer precedence, and whether user configuration is enabled.
- Describe gateway authentication without resolving credentials, and omit endpoint URLs that are unsuitable for display.
- Document the API and update generated JSON schemas, TypeScript types, and Python models.

## Testing

Add app-server tests for provider discovery, authentication modes, unsafe URL suppression, and configuration editability, plus a Python wire-format round-trip test.

GitOrigin-RevId: 8ba26637cd6bdd075e0e815e88aeeb04c53a2364

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -1174,6 +1174,11 @@ client_request_definitions! {
         serialization: None,
         response: v2::GatewayOAuthCancelResponse,
     },
+    ModelProviderList => "modelProvider/list" {
+        params: v2::ModelProviderListParams,
+        serialization: global_shared_read("config"),
+        response: v2::ModelProviderListResponse,
+    },
     ModelProviderCapabilitiesRead => "modelProvider/capabilities/read" {
         params: v2::ModelProviderCapabilitiesReadParams,
         serialization: None,

codex-rs/app-server-protocol/src/protocol/v2/mod.rs

@@ -22,6 +22,7 @@ mod item;
 mod mcp;
 mod memory;
 mod model;
+mod model_provider;
 mod model_provider_error;
 mod notification;
 mod permissions;
@@ -65,6 +66,7 @@ pub use item::*;
 pub use mcp::*;
 pub use memory::*;
 pub use model::*;
+pub use model_provider::*;
 pub use model_provider_error::*;
 pub use notification::*;
 pub use permissions::*;

codex-rs/app-server-protocol/src/protocol/v2/model_provider.rs

@@ -0,0 +1,89 @@
+//! Model provider discovery and the configuration fields visible to clients.
+
+use crate::JsonSchema;
+use crate::TS;
+use serde::Deserialize;
+use serde::Serialize;
+
+#[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ModelProviderListParams {}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ModelProviderListResponse {
+    pub data: Vec<ModelProviderSummary>,
+    pub default_provider_id: String,
+    pub can_change_default: bool,
+}
+
+#[derive(Serialize, Deserialize, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ModelProviderSummary {
+    pub id: String,
+    pub name: String,
+    /// Whether a supported configuration field can be edited in the active user layer.
+    pub can_edit: bool,
+    /// Null when the endpoint is absent or cannot be safely displayed.
+    pub base_url: Option<String>,
+    pub settings: ProviderSettings,
+}
+
+impl std::fmt::Debug for ModelProviderSummary {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("ModelProviderSummary")
+            .field("id", &self.id)
+            .field("name", &self.name)
+            .field("can_edit", &self.can_edit)
+            .field("base_url", &"[REDACTED]")
+            .field("settings", &self.settings)
+            .finish()
+    }
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(tag = "type", rename_all = "camelCase")]
+#[ts(tag = "type", rename_all = "camelCase", export_to = "v2/")]
+pub enum ProviderSettings {
+    #[serde(rename = "openai")]
+    #[ts(rename = "openai")]
+    OpenAi,
+    CustomGateway {
+        auth: GatewayAuth,
+    },
+    Bedrock {
+        profile: Option<String>,
+        region: Option<String>,
+    },
+    Gcp {
+        #[serde(rename = "projectId")]
+        #[ts(rename = "projectId")]
+        project_id: Option<String>,
+        location: Option<String>,
+        /// Path on the app-server host, without credential-file contents.
+        #[serde(rename = "credentialFile")]
+        #[ts(rename = "credentialFile")]
+        credential_file: Option<String>,
+    },
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(tag = "mode", rename_all = "camelCase")]
+#[ts(tag = "mode", rename_all = "camelCase", export_to = "v2/")]
+pub enum GatewayAuth {
+    None,
+    EnvironmentVariable {
+        #[serde(rename = "envKey")]
+        #[ts(rename = "envKey")]
+        env_key: String,
+    },
+    /// Authentication is configured outside the gateway form. Preserve it on edits.
+    ExternallyConfigured {
+        #[serde(rename = "envKey")]
+        #[ts(rename = "envKey")]
+        env_key: Option<String>,
+    },
+}