perf(process): wake waiters on background completion (#45831)

tests/tools/test_process_registry.py

@@ -5,6 +5,7 @@ import os
 import signal
 import subprocess
 import sys
+import threading
 import time
 import pytest
 from unittest.mock import MagicMock, patch
@@ -266,6 +267,31 @@ class TestOrphanedPipeReconciliation:
         except (ProcessLookupError, PermissionError):
             pass
 
+    def test_wait_wakes_when_session_moves_to_finished(self, registry):
+        """wait() should not sleep for the old 1s polling tick after exit."""
+        s = _make_session(sid="proc_wait_event", output="done")
+        registry._running[s.id] = s
+
+        def finish_later():
+            time.sleep(0.05)
+            s.exited = True
+            s.exit_code = 0
+            with patch.object(registry, "_write_checkpoint"):
+                registry._move_to_finished(s)
+
+        t = threading.Thread(target=finish_later)
+        t.start()
+        start = time.monotonic()
+        try:
+            result = registry.wait(s.id, timeout=5)
+        finally:
+            t.join(timeout=1)
+        elapsed = time.monotonic() - start
+
+        assert result["status"] == "exited", result
+        assert result["exit_code"] == 0
+        assert elapsed < 0.3, f"wait() should wake on completion; took {elapsed:.3f}s"
+
 
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