feat(theme): a themed boot splash, and amdgpu back in the ThinkPad's initrd

DECISIONS.md

@@ -1,5 +1,47 @@
 # Decisions
 
+## 2026-09-25 – amdgpu back in the ThinkPad's initrd, for Plymouth's sake
+
+- **Who**: Dominik, ClaudeCode
+- **Why**: With the splash enabled, Plymouth came up on eDP-1 in the mode the
+  firmware had left behind, stretched over a panel with four times the pixels.
+  The boot log has both halves: `simpledrm` owns the framebuffer while the
+  initrd runs, and amdgpu only takes eDP-1 twenty-five seconds later, on the way
+  into the real root. Plymouth draws in the initrd, so it never saw the panel's
+  own resolution. The cause was `hardware.amdgpu.initrd.enable = false`, set on
+  this host to keep the LUKS passphrase prompt in the firmware's large text mode
+  rather than at 3840x2400, where the 8x16 console font is a fifth as tall.
+- **Tradeoffs**: The two wants are opposed — the console text is readable in the
+  firmware mode, Plymouth is only sharp in the native one. Plymouth draws the
+  passphrase prompt itself and scales with the panel, so as long as it runs the
+  text mode buys nothing; with `plymouth.enable=0` on the kernel line, or a
+  Plymouth that fails, the tiny prompt is back. That case is rare and reachable,
+  the splash is every boot.
+- **How**: The line is gone rather than set to `true`: nixos-hardware's amd
+  profile already sets `lib.mkDefault true`, and a build without it comes out at
+  the same store path. A comment in its place records what dropping it costs, so
+  the reasoning is not lost with the line.
+
+## 2026-09-25 – A boot splash, themed from nixpkgs rather than a new flake input
+
+- **Who**: Dominik, ClaudeCode
+- **Why**: The boot was the one part of the system still showing stock text,
+  the LUKS passphrase prompt among it. With systemd in the initrd, Plymouth
+  draws that prompt itself, so the splash covers the whole way from firmware to
+  the greeter rather than stopping at the disk.
+- **Tradeoffs**: (1) **catppuccin/nix** offers `catppuccin.plymouth.enable`,
+  but this flake does not have that input, and taking it on for a boot splash
+  means carrying a second theming source next to the packages already used
+  here. (2) **nixpkgs' `catppuccin-plymouth`** is the same upstream theme as a
+  plain package, with a `variant` argument and no new input. Chosen. (3) The
+  cost either way is that boot messages are hidden, so a stalled boot shows a
+  still image first; `plymouth.enable=0` on the kernel line takes it back
+  without rebuilding, and the previous generation is in the boot menu.
+- **How**: `boot.plymouth` in `modules/theme.nix`, beside the other theme
+  packages, on flavour Mocha like them. `quiet` was already on the kernel
+  command line and the module adds `splash` on its own, so the kernel
+  parameters needed no change.
+
 ## 2026-09-25 – One portal config, and the file dialog on the GTK backend
 
 - **Who**: Dominik, ClaudeCode

README.md

@@ -26,7 +26,7 @@ modules/
   user.nix           moonarch.user option, set per host
   disk.nix           partitioning: GPT, optional LUKS2, btrfs subvolumes
   desktop.nix        compositor, /etc deployment, portals, the rest of the packages
-  theme.nix          GTK, Qt, Kvantum, cursors, fonts
+  theme.nix          GTK, Qt, Kvantum, Plymouth, cursors, fonts
   browsers.nix       Firefox with its preconfiguration, Chromium, handler
   shell.nix          zsh and the command line tools
   lock.nix           gtklock and its PAM stack

hosts/thinkpad/default.nix

@@ -22,12 +22,16 @@
   boot.kernelPackages = pkgs.linuxPackages_zen;
   boot.kernelParams = [ "quiet" ];
 
-  # nixos-hardware puts amdgpu into the initrd, so the panel is already at its
-  # native 3840x2400 when LUKS asks for the passphrase and the 8x16 console font
-  # is a fifth of the height it has on the firmware framebuffer. Without the
-  # driver the prompt is drawn in the mode the firmware left behind and the
-  # driver loads a moment later, on the way into the real root.
-  hardware.amdgpu.initrd.enable = false;
+  # No hardware.amdgpu.initrd.enable here: nixos-hardware's amd profile already
+  # sets it, so the panel is at its native 3840x2400 by the time LUKS asks for
+  # the passphrase. Plymouth draws in the initrd and needs that — without the
+  # driver it gets the mode the firmware left behind, scaled over a panel with
+  # four times the pixels.
+  #
+  # Setting it to false, as this host did before, buys back the console text
+  # underneath: at 3840x2400 the 8x16 font is a fifth of the height it has on
+  # the firmware framebuffer, so a passphrase prompt that arrives as text —
+  # with Plymouth off, or failed — is barely readable.
 
   networking.hostName = "thinkpad";
   networking.networkmanager.enable = true;

modules/theme.nix

@@ -1,4 +1,4 @@
-# ABOUTME: GTK, Qt, Kvantum, cursors and fonts — the look, in one place.
+# ABOUTME: GTK, Qt, Kvantum, Plymouth, cursors and fonts — the look, in one place.
 # ABOUTME: Same theme derivations the greeter uses, so the two cannot drift apart.
 
 { pkgs, moonarchSrc, moonarchPkgs, moonarchThemes, ... }:
@@ -40,6 +40,12 @@ let
     accent = "lavender";
     variant = "mocha";
   };
+
+  # Mocha like everything else here. The package installs under
+  # share/plymouth/themes/catppuccin-${variant}, which is the name boot.plymouth
+  # asks for. Upstream Catppuccin has no accent variants for Plymouth.
+  plymouthVariant = "mocha";
+  plymouthTheme = pkgs.catppuccin-plymouth.override { variant = plymouthVariant; };
 in
 {
   environment.etc = {
@@ -90,6 +96,17 @@ in
     }];
   };
 
+  # The boot splash. `quiet` is already on the kernel command line and the module
+  # puts `splash` there itself, so nothing else has to change for it to show.
+  # With systemd in the initrd, which this configuration uses, systemd asks for
+  # the LUKS passphrase and Plymouth draws that prompt; the script initrd instead
+  # shows it as text before the splash comes up.
+  boot.plymouth = {
+    enable = true;
+    theme = "catppuccin-${plymouthVariant}";
+    themePackages = [ plymouthTheme ];
+  };
+
   # Qt applications are wrapped, so each one looks for plugins in its own
   # closure and never finds a style installed alongside it — which is why VLC
   # kept coming up in the stock Qt style. Enabling this puts the profile's Qt5