diff --git a/agentydragon/tasks/25-guard-tool-output-sequencing-rust.md b/agentydragon/tasks/25-guard-tool-output-sequencing-rust.md
index 869e0bd582..952aa8d84b 100644
--- a/agentydragon/tasks/25-guard-tool-output-sequencing-rust.md
+++ b/agentydragon/tasks/25-guard-tool-output-sequencing-rust.md
@@ -30,7 +30,7 @@ We will implement the following high-level plan:
 - Add tests under `codex-rs/core/tests/` (e.g. `guard_tool_output_sequencing.rs`) that exercise interleaved input sequences:
   - A user message mid-rollout before tool output, ensuring it is delayed until after the tool result.
   - Normal flow where no buffering is needed.
-  - Cancellation or error-result paths that also trigger a flush of buffered messages.
+  - Cancellation paths (no tool output) inserting a fake "Tool cancelled" tool message and flushing buffered messages.
 
 ## Notes
 
diff --git a/codex-rs/core/src/chat_completions.rs b/codex-rs/core/src/chat_completions.rs
index b2accf9d6b..2e8963b1ee 100644
--- a/codex-rs/core/src/chat_completions.rs
+++ b/codex-rs/core/src/chat_completions.rs
@@ -116,6 +116,18 @@ pub(crate) async fn stream_chat_completions(
         }
     }
 
+    // If a tool invocation was never resolved (e.g. was cancelled), insert a fake cancellation result and flush buffered user inputs
+    if let Some(call_id) = pending_call.take() {
+        messages.push(json!({
+            "role": "tool",
+            "tool_call_id": call_id,
+            "content": "Tool cancelled"
+        }));
+        for msg in buf_user.drain(..) {
+            messages.push(msg);
+        }
+    }
+
     let tools_json = create_tools_json_for_chat_completions_api(prompt, model)?;
     let payload = json!({
         "model": model,
diff --git a/codex-rs/core/src/lib.rs b/codex-rs/core/src/lib.rs
index cc42097523..66523db3cf 100644
--- a/codex-rs/core/src/lib.rs
+++ b/codex-rs/core/src/lib.rs
@@ -27,7 +27,7 @@ mod model_provider_info;
 pub use model_provider_info::ModelProviderInfo;
 pub use model_provider_info::WireApi;
 mod models;
-pub use models::{ContentItem, ReasoningItemReasoningSummary, ResponseItem};
+pub use models::{ContentItem, ReasoningItemReasoningSummary, ResponseItem, FunctionCallOutputPayload};
 pub mod openai_api_key;
 mod openai_tools;
 mod project_doc;
@@ -37,4 +37,4 @@ mod safety;
 mod user_notification;
 pub mod util;
 
-pub use client_common::model_supports_reasoning_summaries;
+pub use client_common::{model_supports_reasoning_summaries, Prompt};
diff --git a/codex-rs/core/tests/guard_tool_output_sequencing.rs b/codex-rs/core/tests/guard_tool_output_sequencing.rs
index e0f6682072..c37c2c6fb2 100644
--- a/codex-rs/core/tests/guard_tool_output_sequencing.rs
+++ b/codex-rs/core/tests/guard_tool_output_sequencing.rs
@@ -1,6 +1,5 @@
 use serde_json::{json, Value};
-use codex_core::client_common::Prompt;
-use codex_core::models::{ResponseItem, ContentItem, FunctionCallOutputPayload};
+use codex_core::{Prompt, ResponseItem, ContentItem, FunctionCallOutputPayload};
 
 /// Reproduce the `messages` JSON construction from `stream_chat_completions`
 fn build_messages(input: Vec<ResponseItem>, model: &str) -> Vec<Value> {