feat(desktop): declare the real disk paths

hosts/desktop carried two SET-VIA-disko-install placeholders, so the file
did not say which disks the machine has. The invalid paths only ever
caught a missing --disk flag, never a wrong one, and paid for it by
leaving the hardware undocumented.

The system disk is the 512G XPG, /home goes on the 1T Crucial;
disko-install --disk main|home still overrides both. The 1T currently
holds an ext4 Data partition, which the install erases.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

DECISIONS.md

@@ -1,5 +1,27 @@
 # Decisions
 
+## 2026-08-20 – The desktop declares its real disks
+
+- **Who**: Dominik, ClaudeCode
+- **Why**: `hosts/desktop` still carried the two `SET-VIA-disko-install--disk-*`
+  placeholders from the entry below, so the file did not say which disks the
+  machine has. The ThinkPad names its disk, and nothing about the desktop's two
+  is secret: read off the machine, the system disk is the 512G
+  `nvme-XPG_GAMMIX_S11_Pro_2K322LAES7JG` and `/home` goes on the 1T
+  `nvme-CT1000P1SSD8_2030E2BAC109`.
+- **Tradeoffs**: The invalid paths were a safety net — a forgotten `--disk`
+  flag failed the install instead of erasing something. That net only ever
+  caught the case of a *missing* flag, and it paid for it by making a rebuild
+  of an installed desktop impossible to evaluate honestly and by leaving the
+  hardware undocumented. With correct paths a forgotten flag installs to the
+  intended disk, which is the outcome the flag would have asked for anyway. A
+  wrong flag was never caught by either variant.
+- **How**: The paths in `hosts/desktop/default.nix`, with the comment now
+  saying where they came from and that `disko-install --disk main|home` still
+  overrides them. Note that the 1T currently holds an ext4 `Data` partition —
+  installing erases it. README's "Adding another machine" step 4 no longer
+  advertises the placeholders.
+
 ## 2026-08-20 – A placeholder ~/.zshrc stops the zsh new-user wizard
 
 - **Who**: Dominik, ClaudeCode

README.md

@@ -147,9 +147,8 @@ the disk may enumerate differently next time.
    ```
 
    Both disks are erased. `disko-install` overrides whatever paths the host
-   file declares, which is why `hosts/desktop` carries invalid placeholders:
-   forgetting a flag fails the install instead of erasing a disk that was not
-   meant to be touched.
+   file declares, so the flags are what decides which disks are written —
+   compare them against `lsblk` and `ls -l /dev/disk/by-id/` first.
 
 Without a matching `nixos-hardware` profile, set
 `hardware.cpu.intel.updateMicrocode` or `hardware.cpu.amd.updateMicrocode` in

hosts/desktop/default.nix

@@ -4,17 +4,17 @@
 { config, lib, pkgs, ... }:
 
 {
-  # Both device paths are placeholders. disko-install overrides them with
-  # `--disk main <path>` and `--disk home <path>`, so the real paths are read
-  # from lsblk on the machine and never travel into this repository. The values
-  # here are deliberately invalid: without the flags the install fails instead
-  # of erasing whatever happens to be first in the enumeration.
+  # Read off the machine with `ls -l /dev/disk/by-id/`: the 512G XPG is the
+  # system disk, the 1T Crucial carries /home. disko-install still overrides
+  # both with `--disk main <path>` and `--disk home <path>`, so check them
+  # against lsblk before installing — by-id names follow the drive, not the
+  # slot, and a replaced disk changes them.
   moonarch.disk = {
     enable = true;
-    device = "/dev/disk/by-id/SET-VIA-disko-install--disk-main";
+    device = "/dev/disk/by-id/nvme-XPG_GAMMIX_S11_Pro_2K322LAES7JG";
     home = {
       enable = true;
-      device = "/dev/disk/by-id/SET-VIA-disko-install--disk-home";
+      device = "/dev/disk/by-id/nvme-CT1000P1SSD8_2030E2BAC109";
     };
   };