test(agentcompat): add process supervision harness

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

integration/agentcompat/internal/process/fd_path.go

@@ -0,0 +1,37 @@
+//go:build linux
+
+package process
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+func ProcessHasOpenPath(pid int, path string) (bool, error) {
+	if pid < 1 || !filepath.IsAbs(path) {
+		return false, errors.New("invalid process path query")
+	}
+	directory := filepath.Join("/proc", strconv.Itoa(pid), "fd")
+	entries, err := os.ReadDir(directory)
+	if err != nil {
+		return false, err
+	}
+	wanted := filepath.Clean(path)
+	for _, entry := range entries {
+		target, err := os.Readlink(filepath.Join(directory, entry.Name()))
+		if err != nil {
+			if os.IsNotExist(err) {
+				continue
+			}
+			return false, err
+		}
+		target = strings.TrimSuffix(target, " (deleted)")
+		if filepath.IsAbs(target) && filepath.Clean(target) == wanted {
+			return true, nil
+		}
+	}
+	return false, nil
+}