[codex] add developer instructions (#5897)

we are using developer instructions for code reviews, we need to pass
them in cli as well.

codex-rs/mcp-server/src/codex_tool_config.rs

@@ -50,6 +50,10 @@ pub struct CodexToolCallParam {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub base_instructions: Option<String>,
 
+    /// Developer instructions that should be injected as a developer role message.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub developer_instructions: Option<String>,
+
     /// Prompt used when compacting the conversation.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub compact_prompt: Option<String>,
@@ -145,6 +149,7 @@ impl CodexToolCallParam {
             sandbox,
             config: cli_overrides,
             base_instructions,
+            developer_instructions,
             compact_prompt,
         } = self;
 
@@ -159,6 +164,7 @@ impl CodexToolCallParam {
             model_provider: None,
             codex_linux_sandbox_exe,
             base_instructions,
+            developer_instructions,
             compact_prompt,
             include_apply_patch_tool: None,
             include_view_image_tool: None,
@@ -294,6 +300,10 @@ mod tests {
                 "description": "The set of instructions to use instead of the default ones.",
                 "type": "string"
               },
+              "developer-instructions": {
+                "description": "Developer instructions that should be injected as a developer role message.",
+                "type": "string"
+              },
               "compact-prompt": {
                 "description": "Prompt used when compacting the conversation.",
                 "type": "string"

codex-rs/mcp-server/tests/suite/codex_tool.rs

@@ -341,6 +341,7 @@ async fn codex_tool_passes_base_instructions() -> anyhow::Result<()> {
         .send_codex_tool_call(CodexToolCallParam {
             prompt: "How are you?".to_string(),
             base_instructions: Some("You are a helpful assistant.".to_string()),
+            developer_instructions: Some("Foreshadow upcoming tool calls.".to_string()),
             ..Default::default()
         })
         .await?;
@@ -367,10 +368,28 @@ async fn codex_tool_passes_base_instructions() -> anyhow::Result<()> {
     );
 
     let requests = server.received_requests().await.unwrap();
-    let request = requests[0].body_json::<serde_json::Value>().unwrap();
+    let request = requests[0].body_json::<serde_json::Value>()?;
     let instructions = request["messages"][0]["content"].as_str().unwrap();
     assert!(instructions.starts_with("You are a helpful assistant."));
 
+    let developer_msg = request["messages"]
+        .as_array()
+        .and_then(|messages| {
+            messages
+                .iter()
+                .find(|msg| msg.get("role").and_then(|role| role.as_str()) == Some("developer"))
+        })
+        .unwrap();
+    let developer_content = developer_msg
+        .get("content")
+        .and_then(|value| value.as_str())
+        .unwrap();
+    assert!(
+        !developer_content.contains('<'),
+        "expected developer instructions without XML tags, got `{developer_content}`"
+    );
+    assert_eq!(developer_content, "Foreshadow upcoming tool calls.");
+
     Ok(())
 }