feat: add filemanager session and crypto version detection (#516)

* feat: add filemanager session and crypto version detection

* refactor: move copy logic into filemanager, remove fileutil dependency

* fix: apply review suggestions for filemanager

* feat: add Windows locked file tests, fix readFileContent with ReadFile+FileMapping fallback

* fix: remove self-PID skip in findFileHandle to fix Windows CI test

* fix: seek to file start before reading duplicated handle

* fix: use full path matching in findFileHandle to avoid cross-app handle collision

* test: enhance Windows copyLocked tests with write-then-read, large file, and normal copy scenarios

* fix: check all errors in Windows tests, use bytes.Equal for large file comparison

* fix: use stable path suffix matching to handle Windows short path names in CI

crypto/version.go

@@ -0,0 +1,41 @@
+package crypto
+
+// CipherVersion represents the encryption version used by Chromium browsers.
+type CipherVersion string
+
+const (
+	// CipherV10 is Chrome 80+ encryption (AES-GCM on Windows, AES-CBC on macOS/Linux).
+	CipherV10 CipherVersion = "v10"
+
+	// CipherV20 is Chrome 127+ App-Bound Encryption.
+	CipherV20 CipherVersion = "v20"
+
+	// CipherDPAPI is pre-Chrome 80 raw DPAPI encryption (no version prefix).
+	CipherDPAPI CipherVersion = "dpapi"
+)
+
+// DetectVersion identifies the encryption version from a ciphertext prefix.
+func DetectVersion(ciphertext []byte) CipherVersion {
+	if len(ciphertext) < 3 {
+		return CipherDPAPI
+	}
+	prefix := string(ciphertext[:3])
+	switch prefix {
+	case "v10":
+		return CipherV10
+	case "v20":
+		return CipherV20
+	default:
+		return CipherDPAPI
+	}
+}
+
+// StripPrefix removes the version prefix (e.g. "v10") from ciphertext.
+// Returns the ciphertext unchanged if no known prefix is found.
+func StripPrefix(ciphertext []byte) []byte {
+	ver := DetectVersion(ciphertext)
+	if ver == CipherV10 || ver == CipherV20 {
+		return ciphertext[3:]
+	}
+	return ciphertext
+}