fix: periodic cProfile dump every 60s (survives hard kills)

Replace cProfile.runctx with Profile() + daemon thread that dumps
stats to disk every 60 seconds. Final dump on clean exit. Profile
data no longer lost on container stop, OOM, or SIGKILL.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/derp/cli.py

@@ -193,10 +193,32 @@ def main(argv: list[str] | None = None) -> int:
 
     if args.cprofile:
         import cProfile
+        import threading
 
-        log.info("cProfile enabled, output: %s", args.cprofile)
-        cProfile.runctx("_run(bots)", globals(), {"bots": bots, "_run": _run}, args.cprofile)
-        log.info("profile saved to %s", args.cprofile)
+        prof = cProfile.Profile()
+        prof_path = args.cprofile
+        prof_interval = 60  # dump every 60 seconds
+        prof_stop = threading.Event()
+
+        def _periodic_dump():
+            while not prof_stop.wait(prof_interval):
+                try:
+                    prof.dump_stats(prof_path)
+                except Exception:
+                    pass
+
+        dumper = threading.Thread(target=_periodic_dump, daemon=True)
+        dumper.start()
+        log.info("cProfile enabled, output: %s (saves every %ds)",
+                 prof_path, prof_interval)
+        prof.enable()
+        try:
+            _run(bots)
+        finally:
+            prof.disable()
+            prof_stop.set()
+            prof.dump_stats(prof_path)
+        log.info("profile saved to %s", prof_path)
     else:
         _run(bots)