fix(runtime): stop closing s.Events in Stop; use Base.StopWatcher (#3)

The events channel is closed by code.Watcher.Start's `defer close` (the
sole sender/closer). Stop also closing it raced that goroutine into a
"close of closed channel" panic on shutdown, crashing the agent. Cancel
the watcher via Base.StopWatcher() and let its deferred close run once.

Requires core with services.Base.StopWatcher (codefly-dev/core#49); the
go.mod bump lands with the next core publish.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: AntoineToussaint

runtime.go

@@ -379,13 +379,10 @@ func (s *Runtime) Stop(ctx context.Context, req *runtimev0.StopRequest) (*runtim
 			s.Wool.Warn("error shutting down runner environment", wool.ErrField(err))
 		}
 	}
-	if s.Watcher != nil {
-		s.Watcher.Pause()
-	}
-	if s.Events != nil {
-		close(s.Events)
-		s.Events = nil
-	}
+	// Cancel the watcher and let its Start goroutine's deferred close of Events
+	// run exactly once — Stop must not close Events itself, or it races that
+	// goroutine into a "close of closed channel" panic.
+	s.Base.StopWatcher()
 	return s.Base.Runtime.StopResponse()
 }