diff --git a/src/io_pool.py b/src/io_pool.py
index 51c56d15..f05395c1 100644
--- a/src/io_pool.py
+++ b/src/io_pool.py
@@ -1,3 +1,19 @@
+"""Shared AppController I/O pool factory.
+
+Historical note: an earlier revision of this module registered an
+``atexit.register(pool.shutdown, wait=False)`` handler here, mirroring
+the conftest fix at commit 8957c9a5. That approach was reverted because
+it does not solve the Ctrl+C hang in ``sloppy.py`` when a worker is
+mid-task (e.g. a long-running Gemini/Anthropic HTTP request): atexit
+handlers do not fire at all in that scenario, so the process still hangs
+in ``ThreadPoolExecutor.__del__`` -> ``shutdown(wait=True)`` during
+finalization.
+
+The production fix lives in ``AppController.__init__`` as a SIGINT
+handler that drains the pool and calls ``os._exit(0)``, sidestepping
+the broken finalization chain. See commit log for details.
+"""
+
 from concurrent.futures import ThreadPoolExecutor