feat(tools): seed guest state at boot so captures render wallpapers (item 28c)

theme-shot guests had no ~/.nomarchy, so the session's exec-once
`nomarchy-theme-sync wallpaper` died on missing state and captures
showed a bare base-color backdrop. Seed theme-state.json via tmpfiles
before greetd starts the session — the real exec-once path now paints.
(A post-boot testScript seed is too late for exec-once, and a manual
re-run fails without WAYLAND_DISPLAY: awww's client socket is
display-named.)

V2: summer-night capture renders wallpaper + inverted cream bar +
menu + placeholder dim, all coherent.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tools/theme-shot.nix

@@ -4,10 +4,11 @@
 # Maintainer tool, NOT a checks.* gate (a full-desktop VM is far too
 # heavy for CI). Impure: THEME env picks the theme slug.
 #   THEME=<slug> nix build --impure -f tools/theme-shot.nix --no-link --print-out-paths
-# Known gap: the wallpaper does not paint — nomarchy-theme-sync resolves
-# state from ~/.nomarchy at runtime, absent in the guest; seed it
-# (cp the flake to ~nomarchy/.nomarchy in testScript) if the wallpaper
-# matters to the shot. Bar + menus render fully.
+# The guest gets a minimal ~/.nomarchy (just the theme JSON as
+# theme-state.json), seeded via tmpfiles BEFORE greetd starts the
+# session, so the session's own exec-once wallpaper paint works —
+# assets come from the themesDir baked into the tool. Bar, menus AND
+# wallpaper render.
 let
   flake = builtins.getFlake ("git+file://" + toString ../.);
   inherit (flake.inputs) nixpkgs home-manager;
@@ -38,6 +39,14 @@ pkgs.testers.runNixOSTest {
       extraGroups = [ "wheel" "video" ];
     };
     nomarchy.system.stateFile = flake + "/themes/${slug}.json";
+    # Seed the runtime state (theme-sync reads $NOMARCHY_PATH, default
+    # ~/.nomarchy) before greetd auto-starts the session, so the
+    # exec-once `nomarchy-theme-sync wallpaper` finds it and paints.
+    # NixOS activation creates /home/nomarchy before systemd runs.
+    systemd.tmpfiles.rules = [
+      "d /home/nomarchy/.nomarchy 0755 nomarchy users -"
+      "C /home/nomarchy/.nomarchy/theme-state.json 0644 nomarchy users - ${flake + "/themes/${slug}.json"}"
+    ];
     services.greetd.settings.initial_session = {
       command = "start-hyprland";
       user = "nomarchy";
@@ -52,10 +61,9 @@ pkgs.testers.runNixOSTest {
   testScript = ''
     machine.wait_for_unit("multi-user.target")
     machine.wait_for_file("/run/user/1000/hypr", 180)
-    machine.sleep(12)
-    # Paint the wallpaper explicitly (awww timing was flaky in the spike).
-    machine.execute("su - nomarchy -c 'XDG_RUNTIME_DIR=/run/user/1000 nomarchy-theme-sync wallpaper' >/dev/null 2>&1")
-    machine.sleep(18)
+    # The session exec-once paints the wallpaper (softGL first paint at
+    # 1920x1080 is slow) — give it a generous settle.
+    machine.sleep(30)
     machine.screenshot("desktop")
     # Open the root menu for the polish review.
     hy = "su - nomarchy -c 'XDG_RUNTIME_DIR=/run/user/1000 HYPRLAND_INSTANCE_SIGNATURE=$(ls /run/user/1000/hypr | head -1) hyprctl dispatch exec"