inline model instructions in initial context

codex-rs/codex-api/src/common.rs

@@ -26,8 +26,8 @@ pub const WS_REQUEST_HEADER_TRACESTATE_CLIENT_METADATA_KEY: &str = "ws_request_h
 pub struct CompactionInput<'a> {
     pub model: &'a str,
     pub input: &'a [ResponseItem],
-    #[serde(skip_serializing_if = "str::is_empty")]
-    pub instructions: &'a str,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub instructions: Option<&'a str>,
     pub tools: Vec<Value>,
     pub parallel_tool_calls: bool,
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -182,8 +182,8 @@ impl From<VerbosityConfig> for OpenAiVerbosity {
 #[derive(Debug, Serialize, Clone, PartialEq)]
 pub struct ResponsesApiRequest {
     pub model: String,
-    #[serde(skip_serializing_if = "String::is_empty")]
-    pub instructions: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub instructions: Option<String>,
     pub input: Vec<ResponseItem>,
     pub tools: Vec<serde_json::Value>,
     pub tool_choice: String,
@@ -228,8 +228,8 @@ impl From<&ResponsesApiRequest> for ResponseCreateWsRequest {
 #[derive(Debug, Serialize)]
 pub struct ResponseCreateWsRequest {
     pub model: String,
-    #[serde(skip_serializing_if = "String::is_empty")]
-    pub instructions: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub instructions: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub previous_response_id: Option<String>,
     pub input: Vec<ResponseItem>,

codex-rs/codex-api/src/endpoint/responses_websocket.rs

@@ -806,7 +806,7 @@ mod tests {
     fn direct_serialization_preserves_websocket_request_payload() {
         let request = ResponsesWsRequest::ResponseCreate(ResponseCreateWsRequest {
             model: "gpt-test".to_string(),
-            instructions: "Use the available tools.".to_string(),
+            instructions: Some("Use the available tools.".to_string()),
             previous_response_id: Some("resp-1".to_string()),
             input: vec![ResponseItem::Message {
                 id: Some("msg-1".to_string()),

codex-rs/codex-api/tests/clients.rs

@@ -307,7 +307,7 @@ async fn responses_client_stream_request_preserves_item_ids() -> Result<()> {
     let client = ResponsesClient::new(transport, provider("openai"), Arc::new(NoAuth));
     let request = ResponsesApiRequest {
         model: "gpt-test".into(),
-        instructions: "Say hi".into(),
+        instructions: Some("Say hi".into()),
         input: vec![ResponseItem::Message {
             id: Some("msg_1".into()),
             role: "user".into(),
@@ -399,7 +399,7 @@ async fn streaming_client_retries_on_transport_error() -> Result<()> {
 
     let request = ResponsesApiRequest {
         model: "gpt-test".into(),
-        instructions: "Say hi".into(),
+        instructions: Some("Say hi".into()),
         input: Vec::new(),
         tools: Vec::new(),
         tool_choice: "auto".into(),
@@ -512,7 +512,7 @@ async fn azure_store_sends_ids_and_headers() -> Result<()> {
 
     let request = ResponsesApiRequest {
         model: "gpt-test".into(),
-        instructions: "Say hi".into(),
+        instructions: Some("Say hi".into()),
         input: vec![ResponseItem::Message {
             id: Some("msg_1".into()),
             role: "user".into(),