diff --git a/codex-rs/core/src/chat_completions.rs b/codex-rs/core/src/chat_completions.rs
index 785a4d4ce5..ff88fbf0fe 100644
--- a/codex-rs/core/src/chat_completions.rs
+++ b/codex-rs/core/src/chat_completions.rs
@@ -329,6 +329,140 @@ pub(crate) async fn stream_chat_completions(
         }
     }
 
+    // Validate tool call protocol: ensure all tool_calls have responses and correct ordering.
+    // Collect all tool_call_ids from assistant messages with tool_calls.
+    let mut expected_tool_call_ids = std::collections::HashSet::new();
+    for msg in &messages {
+        if let Some(obj) = msg.as_object() {
+            if obj.get("role").and_then(|v| v.as_str()) == Some("assistant")
+                && let Some(tool_calls) = obj.get("tool_calls").and_then(|v| v.as_array())
+            {
+                for tc in tool_calls {
+                    if let Some(id) = tc.get("id").and_then(|v| v.as_str()) {
+                        expected_tool_call_ids.insert(id.to_string());
+                    }
+                }
+            }
+        }
+    }
+
+    // Collect all tool_call_ids from tool response messages.
+    let mut provided_tool_call_ids = std::collections::HashSet::new();
+    for msg in &messages {
+        if let Some(obj) = msg.as_object() {
+            if obj.get("role").and_then(|v| v.as_str()) == Some("tool")
+                && let Some(id) = obj.get("tool_call_id").and_then(|v| v.as_str())
+            {
+                provided_tool_call_ids.insert(id.to_string());
+            }
+        }
+    }
+
+    // Remove assistant messages with incomplete tool calls (no matching responses).
+    // Also collect tool_call_ids from assistant messages that will be removed.
+    let incomplete_ids: Vec<String> = expected_tool_call_ids
+        .difference(&provided_tool_call_ids)
+        .cloned()
+        .collect();
+
+    let mut removed_assistant_call_ids = std::collections::HashSet::new();
+
+    if !incomplete_ids.is_empty() {
+        messages.retain(|msg| {
+            if let Some(obj) = msg.as_object() {
+                if obj.get("role").and_then(|v| v.as_str()) == Some("assistant")
+                    && let Some(tool_calls) = obj.get("tool_calls").and_then(|v| v.as_array())
+                {
+                    // Check if this assistant message has any incomplete tool calls.
+                    for tc in tool_calls {
+                        if let Some(id) = tc.get("id").and_then(|v| v.as_str()) {
+                            if incomplete_ids.contains(&id.to_string()) {
+                                // Collect ALL tool_call_ids from this assistant message.
+                                // We need to remove their corresponding tool responses too.
+                                for tc2 in tool_calls {
+                                    if let Some(id2) = tc2.get("id").and_then(|v| v.as_str()) {
+                                        removed_assistant_call_ids.insert(id2.to_string());
+                                    }
+                                }
+                                return false;
+                            }
+                        }
+                    }
+                }
+            }
+            true
+        });
+
+        // Remove tool response messages whose assistant origin was removed.
+        messages.retain(|msg| {
+            if let Some(obj) = msg.as_object() {
+                if obj.get("role").and_then(|v| v.as_str()) == Some("tool") {
+                    if let Some(tool_call_id) = obj.get("tool_call_id").and_then(|v| v.as_str()) {
+                        if removed_assistant_call_ids.contains(tool_call_id) {
+                            return false;
+                        }
+                    }
+                }
+            }
+            true
+        });
+    }
+
+    // Enforce sequence ordering: OpenAI protocol requires assistant messages with tool_calls
+    // to be immediately followed by tool response messages. Remove any messages that violate
+    // this constraint.
+    let mut i = 0;
+    while i < messages.len() {
+        if let Some(obj) = messages[i].as_object() {
+            if obj.get("role").and_then(|v| v.as_str()) == Some("assistant")
+                && obj.contains_key("tool_calls")
+            {
+                // Extract all tool_call_ids from this message.
+                let mut call_ids = std::collections::HashSet::new();
+                if let Some(tool_calls) = obj.get("tool_calls").and_then(|v| v.as_array()) {
+                    for tc in tool_calls {
+                        if let Some(id) = tc.get("id").and_then(|v| v.as_str()) {
+                            call_ids.insert(id.to_string());
+                        }
+                    }
+                }
+
+                // Scan forward to find all corresponding tool responses.
+                let mut j = i + 1;
+                let mut found_responses = std::collections::HashSet::new();
+
+                while j < messages.len() {
+                    if let Some(next_obj) = messages[j].as_object() {
+                        let next_role = next_obj.get("role").and_then(|v| v.as_str());
+
+                        if next_role == Some("tool") {
+                            // Accumulate tool responses.
+                            if let Some(tool_call_id) = next_obj.get("tool_call_id").and_then(|v| v.as_str()) {
+                                if call_ids.contains(tool_call_id) {
+                                    found_responses.insert(tool_call_id.to_string());
+                                }
+                            }
+                            j += 1;
+                        } else {
+                            // Non-tool message encountered.
+                            if found_responses.len() < call_ids.len() {
+                                // Incomplete sequence: remove the intruding message.
+                                messages.remove(j);
+                                continue;
+                            } else {
+                                // All responses found, this is the next turn.
+                                break;
+                            }
+                        }
+                    } else {
+                        j += 1;
+                    }
+                }
+            }
+        }
+        i += 1;
+    }
+
     let tools_json = create_tools_json_for_chat_completions_api(&prompt.tools)?;
     let payload = json!({
         "model": model_family.slug,