Parse reasoning text content (#2277)

Sometimes COT is returns as text content instead of `ReasoningText`. We
should parse it but not serialize back on requests.

---------

Co-authored-by: Ahmed Ibrahim <aibrahim@openai.com>

codex-rs/core/src/codex.rs

@@ -1606,6 +1606,7 @@ async fn handle_response_item(
                 for item in content {
                     let text = match item {
                         ReasoningItemContent::ReasoningText { text } => text,
+                        ReasoningItemContent::Text { text } => text,
                     };
                     let event = Event {
                         id: sub_id.to_string(),

codex-rs/core/src/models.rs

@@ -45,7 +45,7 @@ pub enum ResponseItem {
     Reasoning {
         id: String,
         summary: Vec<ReasoningItemReasoningSummary>,
-        #[serde(default, skip_serializing_if = "Option::is_none")]
+        #[serde(default, skip_serializing_if = "should_serialize_reasoning_content")]
         content: Option<Vec<ReasoningItemContent>>,
         encrypted_content: Option<String>,
     },
@@ -81,6 +81,15 @@ pub enum ResponseItem {
     Other,
 }
 
+fn should_serialize_reasoning_content(content: &Option<Vec<ReasoningItemContent>>) -> bool {
+    match content {
+        Some(content) => !content
+            .iter()
+            .any(|c| matches!(c, ReasoningItemContent::ReasoningText { .. })),
+        None => false,
+    }
+}
+
 impl From<ResponseInputItem> for ResponseItem {
     fn from(item: ResponseInputItem) -> Self {
         match item {
@@ -142,6 +151,7 @@ pub enum ReasoningItemReasoningSummary {
 #[serde(tag = "type", rename_all = "snake_case")]
 pub enum ReasoningItemContent {
     ReasoningText { text: String },
+    Text { text: String },
 }
 
 impl From<Vec<InputItem>> for ResponseInputItem {