chore: implement phase 9

grafana-alertcheck/internal/gate/check_process.go

@@ -0,0 +1,29 @@
+package gate
+
+import (
+	"errors"
+	"fmt"
+	"syscall"
+)
+
+// signalRecorder asks the recorder to stop (§4.4 step 2).
+//
+// The caller must have established that a writer is alive — by taking the
+// log's flock and being refused — before it calls this. Nothing removes the
+// pidfile when a recorder exits cleanly, so a pid read without that proof can
+// name any same-user process that has since inherited it.
+//
+// gone reports ESRCH. Given the lock proof, that is a broken contract rather
+// than a clean stop, and stopRecorder treats it as one; the value is reported
+// instead of raised here because this function knows the errno and not what
+// it means.
+func signalRecorder(pid int) (gone bool, err error) {
+	switch err := syscall.Kill(pid, syscall.SIGTERM); {
+	case err == nil:
+		return false, nil
+	case errors.Is(err, syscall.ESRCH):
+		return true, nil
+	default:
+		return false, fmt.Errorf("signal recorder pid %d: %w", pid, err)
+	}
+}