diff --git a/src/api/completions.rs b/src/api/completions.rs
index 3f9dde0..d0a4f6c 100644
--- a/src/api/completions.rs
+++ b/src/api/completions.rs
@@ -78,6 +78,12 @@ pub(crate) async fn handle_completions(
         }
     };
 
+    // Clear any stale tool definitions from other endpoints (e.g. /v1/responses)
+    // to prevent them leaking into completions requests. The completions endpoint
+    // does not support our custom tool call flow, so tools must never be injected.
+    state.mitm_store.clear_tools().await;
+    state.mitm_store.clear_active_function_call();
+
     let token = state.backend.oauth_token().await;
     if token.is_empty() {
         return err_response(
diff --git a/src/mitm/store.rs b/src/mitm/store.rs
index 8144cb0..f497721 100644
--- a/src/mitm/store.rs
+++ b/src/mitm/store.rs
@@ -252,6 +252,11 @@ impl MitmStore {
         self.has_active_function_call.load(Ordering::SeqCst)
     }
 
+    /// Force-clear the active function call flag (used to reset stale state).
+    pub fn clear_active_function_call(&self) {
+        self.has_active_function_call.store(false, Ordering::SeqCst);
+    }
+
     /// Check if there are pending function calls for a cascade.
     pub async fn has_pending_function_calls(&self, cascade_id: &str) -> bool {
         let pending = self.pending_function_calls.read().await;