diff --git a/tests/tools/test_voice_cli_integration.py b/tests/tools/test_voice_cli_integration.py
index 38a947b66a..b3cafede9a 100644
--- a/tests/tools/test_voice_cli_integration.py
+++ b/tests/tools/test_voice_cli_integration.py
@@ -674,3 +674,30 @@ class TestChatTTSCleanupOnException:
                     "chat() must have a finally block cleaning up "
                     "text_queue/stop_event/tts_thread"
                 )
+
+
+class TestBrowserToolSignalHandlerRemoved:
+    """browser_tool.py must NOT register SIGINT/SIGTERM handlers that call
+    sys.exit() — this conflicts with prompt_toolkit's event loop and causes
+    the process to become unkillable during voice mode."""
+
+    def test_no_signal_handler_registration(self):
+        """Source check: browser_tool.py must not call signal.signal()
+        for SIGINT or SIGTERM."""
+        with open("tools/browser_tool.py") as f:
+            source = f.read()
+
+        lines = source.split("\n")
+        for i, line in enumerate(lines, 1):
+            stripped = line.strip()
+            # Skip comments
+            if stripped.startswith("#"):
+                continue
+            assert "signal.signal(signal.SIGINT" not in stripped, (
+                f"browser_tool.py:{i} registers SIGINT handler — "
+                f"use atexit instead to avoid prompt_toolkit conflicts"
+            )
+            assert "signal.signal(signal.SIGTERM" not in stripped, (
+                f"browser_tool.py:{i} registers SIGTERM handler — "
+                f"use atexit instead to avoid prompt_toolkit conflicts"
+            )
diff --git a/tools/browser_tool.py b/tools/browser_tool.py
index 15f4961897..b3516c4f24 100644
--- a/tools/browser_tool.py
+++ b/tools/browser_tool.py
@@ -224,24 +224,14 @@ def _emergency_cleanup_all_sessions():
         logger.error("Emergency cleanup error: %s", e)
 
 
-def _signal_handler(signum, frame):
-    """Handle interrupt signals to cleanup sessions before exit."""
-    logger.warning("Received signal %s, cleaning up...", signum)
-    _emergency_cleanup_all_sessions()
-    sys.exit(128 + signum)
-
-
-# Register cleanup handlers
+# Register cleanup via atexit only.  Previous versions installed SIGINT/SIGTERM
+# handlers that called sys.exit(), but this conflicts with prompt_toolkit's
+# async event loop — a SystemExit raised inside a key-binding callback
+# corrupts the coroutine state and makes the process unkillable.  atexit
+# handlers run on any normal exit (including sys.exit), so browser sessions
+# are still cleaned up without hijacking signals.
 atexit.register(_emergency_cleanup_all_sessions)
 
-# Only register signal handlers in main process (not in multiprocessing workers)
-try:
-    if os.getpid() == os.getpgrp():  # Main process check
-        signal.signal(signal.SIGINT, _signal_handler)
-        signal.signal(signal.SIGTERM, _signal_handler)
-except (OSError, AttributeError):
-    pass  # Signal handling not available (e.g., Windows or worker process)
-
 
 # =============================================================================
 # Inactivity Cleanup Functions