From b8f494504082d1530d7ab6a04ceced786f5faa29 Mon Sep 17 00:00:00 2001
From: Charles Cunningham <ccunningham@openai.com>
Date: Mon, 23 Mar 2026 12:10:21 -0700
Subject: [PATCH] Drop orphan reasoning items before replay

Trim trailing reasoning items from prompt history before the next user message or prompt end so interrupted turns do not replay invalid Responses API input.

Co-authored-by: Codex <noreply@openai.com>
---
 codex-rs/core/src/context_manager/history.rs  |  6 ++-
 .../core/src/context_manager/history_tests.rs | 53 +++++++++++++++++++
 .../core/src/context_manager/normalize.rs     | 27 ++++++++++
 3 files changed, 85 insertions(+), 1 deletion(-)

diff --git a/codex-rs/core/src/context_manager/history.rs b/codex-rs/core/src/context_manager/history.rs
index f990a80dce..17e7e33c7d 100644
--- a/codex-rs/core/src/context_manager/history.rs
+++ b/codex-rs/core/src/context_manager/history.rs
@@ -333,7 +333,8 @@ impl ContextManager {
     /// This function enforces a couple of invariants on the in-memory history:
     /// 1. every call (function/custom) has a corresponding output entry
     /// 2. every output has a corresponding call entry
-    /// 3. when images are unsupported, image content is stripped from messages and tool outputs
+    /// 3. trailing reasoning items are dropped before the next user message and at prompt end
+    /// 4. when images are unsupported, image content is stripped from messages and tool outputs
     fn normalize_history(&mut self, input_modalities: &[InputModality]) {
         // all function/tool calls must have a corresponding output
         normalize::ensure_call_outputs_present(&mut self.items);
@@ -341,6 +342,9 @@ impl ContextManager {
         // all outputs must have a corresponding function/tool call
         normalize::remove_orphan_outputs(&mut self.items);
 
+        // interrupted turns can leave replay-unsafe trailing reasoning before the next user item
+        normalize::remove_trailing_reasoning_before_user_messages(&mut self.items);
+
         // strip images when model does not support them
         normalize::strip_images_when_unsupported(input_modalities, &mut self.items);
     }
diff --git a/codex-rs/core/src/context_manager/history_tests.rs b/codex-rs/core/src/context_manager/history_tests.rs
index 71b3aded0c..b6bb257bbe 100644
--- a/codex-rs/core/src/context_manager/history_tests.rs
+++ b/codex-rs/core/src/context_manager/history_tests.rs
@@ -442,6 +442,59 @@ fn for_prompt_preserves_image_generation_calls_when_images_are_supported() {
     );
 }
 
+#[test]
+fn for_prompt_drops_trailing_reasoning_before_next_user_message() {
+    let history = create_history_with_items(vec![
+        user_input_text_msg("first"),
+        assistant_msg("done"),
+        reasoning_msg("orphaned"),
+        user_input_text_msg("second"),
+    ]);
+
+    assert_eq!(
+        history.for_prompt(&default_input_modalities()),
+        vec![
+            user_input_text_msg("first"),
+            assistant_msg("done"),
+            user_input_text_msg("second"),
+        ]
+    );
+}
+
+#[test]
+fn for_prompt_drops_trailing_reasoning_at_prompt_end() {
+    let history = create_history_with_items(vec![
+        user_input_text_msg("first"),
+        assistant_msg("done"),
+        reasoning_msg("orphaned"),
+    ]);
+
+    assert_eq!(
+        history.for_prompt(&default_input_modalities()),
+        vec![user_input_text_msg("first"), assistant_msg("done"),]
+    );
+}
+
+#[test]
+fn for_prompt_keeps_reasoning_when_followed_by_assistant_message() {
+    let history = create_history_with_items(vec![
+        user_input_text_msg("first"),
+        reasoning_msg("kept"),
+        assistant_msg("done"),
+        user_input_text_msg("second"),
+    ]);
+
+    assert_eq!(
+        history.for_prompt(&default_input_modalities()),
+        vec![
+            user_input_text_msg("first"),
+            reasoning_msg("kept"),
+            assistant_msg("done"),
+            user_input_text_msg("second"),
+        ]
+    );
+}
+
 #[test]
 fn for_prompt_clears_image_generation_result_when_images_are_unsupported() {
     let history = create_history_with_items(vec![
diff --git a/codex-rs/core/src/context_manager/normalize.rs b/codex-rs/core/src/context_manager/normalize.rs
index 839bae331e..5bb67f5b5d 100644
--- a/codex-rs/core/src/context_manager/normalize.rs
+++ b/codex-rs/core/src/context_manager/normalize.rs
@@ -194,6 +194,33 @@ pub(crate) fn remove_orphan_outputs(items: &mut Vec<ResponseItem>) {
     });
 }
 
+pub(crate) fn remove_trailing_reasoning_before_user_messages(items: &mut Vec<ResponseItem>) {
+    let mut normalized = Vec::with_capacity(items.len());
+    let mut removed_count = 0usize;
+
+    for item in items.drain(..) {
+        if matches!(&item, ResponseItem::Message { role, .. } if role == "user") {
+            while matches!(normalized.last(), Some(ResponseItem::Reasoning { .. })) {
+                normalized.pop();
+                removed_count += 1;
+            }
+        }
+
+        normalized.push(item);
+    }
+
+    while matches!(normalized.last(), Some(ResponseItem::Reasoning { .. })) {
+        normalized.pop();
+        removed_count += 1;
+    }
+
+    if removed_count > 0 {
+        info!("Removed {removed_count} trailing reasoning item(s) before user input or prompt end");
+    }
+
+    *items = normalized;
+}
+
 pub(crate) fn remove_corresponding_for(items: &mut Vec<ResponseItem>, item: &ResponseItem) {
     match item {
         ResponseItem::FunctionCall { call_id, .. } => {