feat: update NewConversationParams to take an optional model_provider

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

@@ -252,6 +252,10 @@ pub struct NewConversationParams {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub model: Option<String>,
 
+    /// Override the model provider to use for this session.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub model_provider: Option<String>,
+
     /// Configuration profile from config.toml to specify default options.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub profile: Option<String>,

codex-rs/app-server/src/codex_message_processor.rs

@@ -1533,6 +1533,7 @@ async fn derive_config_from_params(
 ) -> std::io::Result<Config> {
     let NewConversationParams {
         model,
+        model_provider,
         profile,
         cwd,
         approval_policy,
@@ -1548,7 +1549,7 @@ async fn derive_config_from_params(
         cwd: cwd.map(PathBuf::from),
         approval_policy,
         sandbox_mode,
-        model_provider: None,
+        model_provider,
         codex_linux_sandbox_exe,
         base_instructions,
         include_apply_patch_tool,