feat(ai_client): isolation of current_tier using threading.local() for parallel agent safety

tests/test_ai_client_concurrency.py

@@ -0,0 +1,39 @@
+import threading
+from src import ai_client
+
+def test_ai_client_tier_isolation():
+ original_append = ai_client._append_comms
+ captured_logs = []
+ def intercepted_append(direction, kind, payload):
+  captured_logs.append({
+   'thread_name': threading.current_thread().name,
+   'source_tier': ai_client.get_current_tier()
+  })
+  original_append(direction, kind, payload)
+ ai_client._append_comms = intercepted_append
+ ai_client.clear_comms_log()
+ barrier = threading.Barrier(2)
+ def run_t1():
+  ai_client.set_current_tier('Tier 3')
+  barrier.wait()
+  ai_client._append_comms('OUT', 'test', {})
+ def run_t2():
+  ai_client.set_current_tier('Tier 4')
+  barrier.wait()
+  ai_client._append_comms('OUT', 'test', {})
+ t1 = threading.Thread(target=run_t1, name='T1')
+ t2 = threading.Thread(target=run_t2, name='T2')
+ t1.start()
+ t2.start()
+ t1.join()
+ t2.join()
+ try:
+  log_t1 = next(log for log in captured_logs if log['thread_name'] == 'T1')
+  log_t2 = next(log for log in captured_logs if log['thread_name'] == 'T2')
+  assert log_t1['source_tier'] == 'Tier 3'
+  assert log_t2['source_tier'] == 'Tier 4'
+ finally:
+  ai_client._append_comms = original_append
+
+if __name__ == "__main__":
+ test_ai_client_tier_isolation()