feature(gpg): move git from gpg-signing to ssh-signing

modules/nixos/gnupg.nix

@@ -4,12 +4,28 @@
   # enable gnupg agent
   programs.gnupg.agent = {
     enable = true;
-    enableSSHSupport = true;
-    pinentryPackage = pkgs.pinentry-curses;
+    # a graphical pinentry never grabs the tty, so a passphrase prompt can no
+    # longer take over a terminal that a coding agent is driving
+    pinentryPackage = pkgs.pinentry-qt;
+    settings = {
+      # keep the key unlocked for a full working day instead of 10 minutes,
+      # so signing commits asks at most once per session
+      default-cache-ttl = 86400;
+      max-cache-ttl = 86400;
+      # fail an unattended signature instead of blocking on a prompt forever
+      pinentry-timeout = 120;
+    };
   };
 
-  environment.systemPackages = with pkgs; [ 
+  environment.systemPackages = with pkgs; [
     gnupg
+    pinentry-qt
+    # fallback for sessions without a display, switch pinentryPackage to use it
     pinentry-curses
+    # prime the passphrase cache on demand, e.g. before an agent session
+    (writeShellScriptBin "gpg-unlock" ''
+      echo | ${config.programs.gnupg.package}/bin/gpg --clearsign --output /dev/null
+      echo "gpg key unlocked"
+    '')
   ];
 }