programs: define persistence for Tangram

hosts/common/programs/default.nix

@@ -31,6 +31,7 @@
     ./splatmoji.nix
     ./steam.nix
     ./sublime-music.nix
+    ./tangram.nix
     ./vlc.nix
     ./web-browser.nix
     ./wireshark.nix

hosts/common/programs/tangram.nix

@@ -0,0 +1,13 @@
+# Tangram is a GTK/webkit browser
+# it views each tab as a distinct application, persisted, and where the 'home' button action is specific to each tab.
+# it supports ephemeral tabs, but UX is heavily geared to GCing those as early as possible.
+
+{ ... }:
+{
+  sane.programs.tangram = {
+    persist.private = [
+      ".cache/Tangram"
+      ".local/share/Tangram"
+    ];
+  };
+}