feat: add full snapshot downloads and safe manual restore

internal/api/backup_management.go

@@ -33,6 +33,10 @@ type snapshotInfo struct {
 	Protected        bool      `json:"protected"`
 	ProtectionReason string    `json:"protection_reason"`
 	SizeError        string    `json:"size_error,omitempty"`
+	Restorable       bool      `json:"restorable"`
+	RestoreReason    string    `json:"restore_reason"`
+	SourceVersion    string    `json:"source_version,omitempty"`
+	SourceImage      string    `json:"source_image,omitempty"`
 }
 
 func managementRoot(base string, parts ...string) (*os.Root, error) {
@@ -190,10 +194,18 @@ func (a *API) backupManagement(w http.ResponseWriter, r *http.Request, i store.I
 				return
 			}
 			s := snapshotInfo{ID: entry.Name(), CreatedAt: st.ModTime(), Protected: reason != "", ProtectionReason: reason}
+			s.SourceVersion, s.SourceImage, s.RestoreReason = a.snapshotCompatibility(i, s.ID)
+			s.Restorable = s.RestoreReason == "" || s.RestoreReason == snapshotUnknownReason
+			if reason != "" {
+				s.Restorable = false
+				s.RestoreReason = reason
+			}
 			s.Size, err = snapshotBytes(r.Context(), root, entry.Name())
 			if err != nil {
 				s.Size = -1
 				s.SizeError = "snapshot size unavailable: " + err.Error()
+				s.Restorable = false
+				s.RestoreReason = "snapshot size unavailable"
 			}
 			out = append(out, s)
 		}