feat(hosts): add the Raspberry Pi Zero 2 W Psion sidecar

A headless aarch64 companion for a Psion 5MX: PPP over RS232 with NAT out to
wifi and a telnet login, plus a cleartext POP3/SMTP proxy for the Psion's mail
client.

- hosts/PiZero2W/: host config, serial-ppp.nix, email-proxy.nix, an SD-image
  variant, and a hardware-configuration.nix placeholder.
- Host table entry on nixos-hardware's raspberry-pi-3 profile; the Zero 2 W is
  the Pi 3's BCM2837 SoC. nixpkgs' linuxPackages_rpi02w is deprecated and warns
  that the linux-rpi series is being removed in favour of nixos-hardware.
- The host owns its firmware partition (hardware.raspberry-pi.firmware), which
  is what puts the disable-bt and uart0/ctsrts overlays in config.txt so
  /dev/ttyAMA0 is the RS232 header rather than Bluetooth. uboot.enable keeps the
  U-Boot -> extlinux boot path the rewritten config.txt would otherwise lose.
- packages.aarch64-linux.zero2w-sd-image: the host's own configuration as an
  installable card. The board has no Ethernet and no free serial port, so a
  generic image would leave no way in.
- The mail proxy comes from the legacy-email-proxy flake, which provides the
  package and the NixOS module; nothing about it is vendored here.
- docs/hosts/pizero2w.md, plus README host table and shared-layer notes.

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

README.md

@@ -8,12 +8,13 @@ single flake.
 Defined in the host table in [`flake.nix`](https://code.emmathe.dev/lyrathorpe/nixfiles/src/branch/main/flake.nix):
 
 | Configuration         | System           | Machine                                                                                                                                        |
-| --------------------- | ---------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
+| --------------------- | ---------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- |
 | `lyrathorpe-mbp`      | `aarch64-linux`  | MacBook Pro (Apple Silicon, Asahi)                                                                                                             |
 | `lyrathorpe-t400`     | `x86_64-linux`   | ThinkPad T400 — [install notes](https://docs.lyrapup.pet/nixfiles/hosts/t400/)                                                                 |
 | `lyrathorpe-macpro31` | `x86_64-linux`   | Mac Pro 3,1, desktop — [install notes](https://docs.lyrapup.pet/nixfiles/hosts/macpro31/)                                                      |
 | `emmathorpe-edaas`    | `x86_64-linux`   | Work WSL box (NixOS-WSL) — [notes](https://docs.lyrapup.pet/nixfiles/hosts/edaas/)                                                             |
 | `lyrathorpe-rpi5`     | `aarch64-linux`  | Raspberry Pi 5 headless server: Docker host + nginx reverse proxy — [install notes](https://docs.lyrapup.pet/nixfiles/hosts/rpi5/)             |
+| `lyrathorpe-zero2w`   | `aarch64-linux`  | Raspberry Pi Zero 2 W "Psion sidecar": PPP over RS232 + legacy mail proxy — [install notes](https://docs.lyrapup.pet/nixfiles/hosts/pizero2w/) |
 | `lyrathorpe-mac`      | `aarch64-darwin` | macOS (nix-darwin) — [notes](https://docs.lyrapup.pet/nixfiles/hosts/darwin/)                                                                  |
 
 Shared layers: `home` (home-manager: shell, git, editor),
@@ -21,8 +22,8 @@ Shared layers: `home` (home-manager: shell, git, editor),
 `modules/workstation.nix` (physical graphical hosts: audio, thermald,
 earlyoom, fwupd), `modules/laptop.nix` (laptops: Wi-Fi, Bluetooth, power,
 lid), `modules/desktop.nix` (wired desktops: NetworkManager), and
-`modules/ssh.nix` (key-only sshd). The x86 hosts also pull `nixos-hardware`
+`modules/ssh.nix` (key-only sshd). The x86 hosts and both Raspberry Pis also
-profiles. The full module catalogue is below.
+pull `nixos-hardware` profiles. The full module catalogue is below.
 
 ## Repository layout
 
@@ -57,7 +58,7 @@ module reaches a host: **baseModules** (every NixOS host, via `flake.nix`),
 (pulled in by another module's `imports`).
 
 | Module             | Imported by                          | What it does / when to use it                                                                                                                                                                                                                                                                                                 |
-| ------------------ | --------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| ------------------ | ------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | `common-nixos.nix` | baseModules (all NixOS)              | Timezone/locale, store hygiene (auto-optimise, big download buffer, **no** auto-GC), the nix-community binary cache, `nix-ld`, **sudo-rs** in place of sudo, base CLI (`git`, `fastfetch`), and the fleet-wide font stack.                                                                                                    |
 | `users.nix`        | baseModules (all NixOS)              | Builds `users.users` from the registry for the host's `hostUsers`; enables zsh; enables Firefox + Thunderbird **only** when `features.swayDesktop.enable` is on. Applies per-user `linger`.                                                                                                                                   |
 | `features.nix`     | baseModules (all NixOS)              | Declares the feature-flag options (`features.swayDesktop.enable`, `features.claudeCode.enable`) so any host can read/set them without importing the heavy implementation module, plus the CPU capability fact they derive from (`features.cpu.microarchLevel`) and the assertion that guards it. See "CPU capability gating". |
@@ -65,7 +66,7 @@ module reaches a host: **baseModules** (every NixOS host, via `flake.nix`),
 | `laptop.nix`       | host table (MBP, T400)               | `imports` workstation.nix, then adds the portable bits: iwd Wi-Fi, lid suspend/lock, Bluetooth + blueman.                                                                                                                                                                                                                     |
 | `desktop.nix`      | host table (Mac Pro)                 | `imports` workstation.nix, then swaps Wi-Fi for wired NetworkManager. Pair with `portable = false` in the host table.                                                                                                                                                                                                         |
 | `sway.nix`         | host table (graphical hosts)         | Implementation of `features.swayDesktop`: the system Sway package, the greetd/ReGreet (cage) greeter forced to Dvorak, xdg-portal, Wayland utility packages. Home-side Sway config is in `home/sway.nix`.                                                                                                                     |
-| `ssh.nix`          | host table (T400, Mac Pro, RPi5)  | Enables sshd, opens port 22, enforces a key-only policy (no password / keyboard-interactive, no root). Authorized keys come from the registry via `users.nix`.                                                                                                                                                                |
+| `ssh.nix`          | host table (T400, Mac Pro, both Pis) | Enables sshd, opens port 22, enforces a key-only policy (no password / keyboard-interactive, no root). Authorized keys come from the registry via `users.nix`.                                                                                                                                                                |
 | `firmware/`        | referenced by MBP host config        | Committed Apple peripheral firmware blobs for the Asahi MBP (see "MacBook (Asahi) firmware").                                                                                                                                                                                                                                 |
 
 Form-factor decision: a **laptop** imports `laptop.nix` (default

docs/hosts/pizero2w.md

@@ -0,0 +1,205 @@
+# Raspberry Pi Zero 2 W (`lyrathorpe-zero2w`)
+
+Headless `aarch64-linux` "Psion sidecar": an RS232 companion for a Psion 5MX,
+after [Kian Ryan's PPP modem and terminal
+write-up](https://www.kianryan.co.uk/2022-11-28-psion-sidecar-ppp-modem-and-terminal/).
+Two roles, split into submodules:
+
+- **PPP link + telnet** (`serial-ppp.nix`) — `pppd` on `/dev/ttyAMA0`, the Psion
+  on the far end of a null-modem cable, NAT out to Wi-Fi, and a telnet login for
+  the Psion's terminal client.
+- **Legacy mail proxy** (`email-proxy.nix`) — cleartext POP3/SMTP for the
+  Psion's built-in mail client, forwarded to authenticated IMAPS/SMTPS by
+  [legacy-email-proxy](https://code.emmathe.dev/lyrathorpe/legacy-email-proxy).
+  That project ships its own package and NixOS module, so `email-proxy.nix`
+  here is only `services.legacy-email-proxy.enable` plus a path to the
+  credentials — nothing about the proxy is vendored into this flake.
+
+`sd-image.nix` in the same directory is not part of the running system: it is
+the one-shot install card, built as `packages.aarch64-linux.zero2w-sd-image`.
+See "Install".
+
+## Hardware and boot
+
+The Zero 2 W is a BCM2837 — the Pi 3's SoC — so the host table uses
+`nixos-hardware`'s `raspberry-pi-3` profile for the kernel, firmware and device
+tree. Boot is the same U-Boot + extlinux path as the other Pi.
+
+Unlike the Pi 5, this host owns the firmware partition declaratively
+(`hardware.raspberry-pi.firmware.enable`): every `switch` rewrites
+`/boot/firmware`, including `config.txt`. Two settings there matter:
+
+| `config.txt`             | Why                                                                                                                                                 |
+| ------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `dtoverlay=disable-bt`   | Moves the PL011 UART off Bluetooth onto GPIO 14/15, so `/dev/ttyAMA0` is the RS232 header. The mini UART (`ttyS0`) drifts at 115200.                |
+| `dtoverlay=uart0,ctsrts` | RTS/CTS on GPIO 16/17. Both `pppd` and the Psion's modem profile use hardware flow control.                                                         |
+| `kernel=u-boot.bin`      | `hardware.raspberry-pi.firmware.uboot.enable`. Without it the rewritten `config.txt` would have no `kernel=` line and the board would stop booting. |
+
+`gpu_mem=16`, `start_x=0`, `camera_auto_detect=0` and `display_auto_detect=0`
+hand the VideoCore the minimum: the board has 512 MB total and no display.
+
+## Never build on the Pi
+
+512 MB of RAM and an SD card. It cannot compile its own system, and there is
+deliberately no swap partition (SD cards wear out under swap writes) — zram
+takes its place. Build somewhere else and push the result:
+
+```sh
+# from a workstation, using another aarch64 machine as the builder
+nixos-rebuild switch --flake .#lyrathorpe-zero2w \
+  --build-host lyrathorpe@lyrathorpe-rpi5 \
+  --target-host lyrathorpe@<pi-address> --use-remote-sudo
+```
+
+The `raspberry-pi-3` profile builds the vendor kernel from source and it is not
+in the binary cache, so the first build is long (hours on the Pi 5, less on the
+MacBook). Later builds reuse it. The same applies to the SD image below: it
+contains that kernel, so it needs an `aarch64-linux` builder too. From an
+`x86_64` box or a Mac, that means a remote builder (`nix.buildMachines`) or, on
+Darwin, `nix.linux-builder.enable`.
+
+## Install
+
+The card is built from this flake, not downloaded. A generic NixOS image would
+boot, but there would be no way into the machine afterwards: it has no Ethernet,
+no wifi credentials, and this configuration hands the serial port to `pppd`, so
+there is no console either. Building the host's own image sidesteps all three —
+the first boot is already the real system, with the SSH key from the registry
+in place.
+
+1. **Set the SSID.** `networking.wireless.networks` in `configuration.nix` still
+   says `CHANGE-ME-SSID`. It is baked into the image at build time; only the PSK
+   is read at runtime.
+2. **Build and write the card.** On an `aarch64-linux` machine (or with one
+   configured as a builder):
+   ```sh
+   nix build .#packages.aarch64-linux.zero2w-sd-image
+   sudo dd if=result/sd-image/nixos-zero2w.img of=/dev/sdX bs=4M conv=fsync status=progress
+   ```
+   Check `/dev/sdX` twice. `dd` does not ask.
+3. **Seed the secrets before first boot.** They are not in the image. Mount the
+   card's second partition (the ext4 root) and write both files described under
+   "Secrets" below:
+   ```sh
+   sudo mount /dev/sdX2 /mnt
+   sudo mkdir -p /mnt/var/lib/wpa_supplicant /mnt/var/lib/legacy-email-proxy
+   printf 'psk_home=%s\n' 'the-pre-shared-key' \
+     | sudo tee /mnt/var/lib/wpa_supplicant/secrets.conf > /dev/null
+   sudo chmod 600 /mnt/var/lib/wpa_supplicant/secrets.conf
+   # ... and /mnt/var/lib/legacy-email-proxy/backend.env, same permissions
+   sudo umount /mnt
+   ```
+   Skip the PSK and the board boots with no network at all.
+4. **Boot it.** Give it a few minutes on first boot — it resizes the root
+   partition and generates host keys on a slow card. Then:
+   ```sh
+   ssh lyrathorpe@lyrathorpe-zero2w.local   # mDNS; services.avahi publishes it
+   ```
+5. **Give the login user a password** (`passwd lyrathorpe`) if you want console
+   or telnet login; the SSH key from
+   [`users/registry.nix`](https://code.emmathe.dev/lyrathorpe/nixfiles/src/branch/main/users/registry.nix)
+   already works without one.
+6. Thereafter, rebuild from another machine as in the previous section.
+
+`hosts/PiZero2W/hardware-configuration.nix` is a **placeholder** — but its
+layout (`/` on label `NIXOS_SD`, `/boot/firmware` on label `FIRMWARE`) is
+exactly what the SD image produces, so there is nothing to regenerate for a card
+install. Run `nixos-generate-config` and replace it only if you deviate from
+that layout.
+
+If the board never appears on the network, it is almost always the PSK file.
+Re-mount the card and check it. Failing that, a mini-HDMI monitor and a
+micro-USB keyboard get you a console on `tty1` — the serial port will not,
+because `pppd` holds it.
+
+## Secrets (not in the Nix store)
+
+Both files are created on the device, owned by root, mode `0600`. Neither is
+managed by this flake; the units that read them fail loudly if they are absent.
+
+**Wi-Fi PSK** — `/var/lib/wpa_supplicant/secrets.conf`:
+
+```
+psk_home=<the pre-shared key>
+```
+
+The SSID itself _is_ in `configuration.nix` and is currently the placeholder
+`CHANGE-ME-SSID`; set it to the real network. `wpa_supplicant` resolves
+`pskRaw = "ext:psk_home"` against this file at runtime.
+
+**Mail backend** — `/var/lib/legacy-email-proxy/backend.env`, a systemd
+`EnvironmentFile`:
+
+```
+BACKEND_IMAP_HOST=imap.example.com
+BACKEND_IMAP_USER=someone@example.com
+BACKEND_IMAP_PASS=<app password>
+BACKEND_SMTP_HOST=smtp.example.com
+BACKEND_SMTP_USER=someone@example.com
+BACKEND_SMTP_PASS=<app password>
+```
+
+Ports and TLS default sensibly (IMAPS 993, SMTPS 465); the full variable list is
+in the proxy's README.
+
+### Why POP3 and not IMAP
+
+The Psion's built-in mail client speaks POP only, so POP3 is what the proxy
+exposes. If a third-party IMAP client is ever installed on the device, the
+answer is **not** to add an IMAP frontend to the proxy: the backend is already
+IMAP, so there is no protocol to translate, only TLS to remove. An `stunnel`
+client (plaintext 143 on the PPP link, IMAPS 993 outbound) does that in a few
+lines with no code, and credentials pass straight through — IMAP clients always
+authenticate.
+
+SMTP stays on the proxy either way. A client of this vintage cannot do SMTP
+AUTH, which is exactly why the proxy injects the backend credentials.
+
+## Psion configuration
+
+Matches the addressing in `serial-ppp.nix` (`10.0.0.1` the Pi, `10.0.0.2` the
+Psion):
+
+- **Modem** control panel, a "Direct Cable Connection" profile: 115200 baud,
+  Hardware (RTS/CTS) flow control; on the Advanced tab, Terminal Detect and
+  Carrier Detect both **off**.
+- **Internet** control panel, a new profile: Connection Type **Direct**, Manual
+  Login **True**. Addresses: get IP from server **False**, static **10.0.0.2**.
+  Get DNS from server **True** — `pppd` sends resolvers over the link
+  (`ms-dns`), so nothing is hard-coded on the Psion.
+- Advanced: PPP extensions **False**, plain-text authentication **True**.
+- Terminal client: telnet to **10.0.0.1 port 23**. It renders non-ANSI output
+  far better than the raw serial console does.
+- Mail client: POP3 and SMTP server **10.0.0.1**, no encryption, no
+  authentication.
+
+## Security
+
+Everything on this host that the Psion talks to is unauthenticated and
+unencrypted, because a 1999 palmtop speaks no TLS:
+
+- **telnet on 23** — cleartext login, including the password.
+- **POP3 on 110 / SMTP on 25** — full mailbox access and an open relay to anyone
+  who reaches them.
+
+The confinement is the firewall, and it is the only thing standing there:
+`ppp0` is a trusted interface, `wlan0` is not, and those ports are never opened
+on it. The proxy binds `0.0.0.0` rather than `10.0.0.1` on purpose — the PPP
+address only exists while the Psion is plugged in, and a bind-time dependency on
+a serial cable is a restart loop waiting to happen. Do not add these ports to
+`networking.firewall.allowedTCPPorts`, and do not put this board on an untrusted
+network.
+
+Only sshd (port 22, key-only, via
+[`modules/ssh.nix`](https://code.emmathe.dev/lyrathorpe/nixfiles/src/branch/main/modules/ssh.nix))
+is reachable over Wi-Fi.
+
+## Troubleshooting
+
+| Symptom                                         | Check                                                                                                                                                                            |
+| ----------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| No PPP at all                                   | `systemctl status pppd-psion`, then `journalctl -u pppd-psion -f` while the Psion dials. `passive`/`persist` mean it waits, not fails.                                           |
+| PPP negotiates, then hangs                      | Flow control. Confirm `dtoverlay=uart0,ctsrts` is in `/boot/firmware/config.txt` and that the Psion's modem profile is set to Hardware.                                          |
+| `/dev/ttyAMA0` missing or is a Bluetooth device | `disable-bt` did not apply — the firmware partition was not rewritten. Confirm `/boot/firmware` is a mounted partition; the activation script skips with a warning if it is not. |
+| Something else holds the port                   | `systemctl status serial-getty@ttyAMA0` — it is disabled in `serial-ppp.nix`, and must stay that way.                                                                            |
+| Mail proxy dead                                 | `systemctl status legacy-email-proxy`. A missing `backend.env` fails the unit before it starts.                                                                                  |

docs/shell.md

@@ -186,14 +186,6 @@ fleet's stock "wheel, with a password" policy. What it does **not** implement:
 host aliases, LDAP/SSSD sudoers, `sudoreplay`, and most `Defaults` settings.
 Needing any of those means reverting to `security.sudo`.
 
-One exception to the password: the EDaaS box sets
-`security.sudo-rs.wheelNeedsPassword = false`. NixOS-WSL ships that default for
-`security.sudo` — WSL has no console login, so the trust boundary is the Windows
-session and the Linux account password is never one the user chose — and the
-option does not carry across to the `security.sudo-rs` module, which defaults to
-requiring one. Without the explicit setting, `sudo` on that host prompts for a
-password nobody knows.
-
 If a host ever refuses to escalate, get a root shell that does not go through
 sudo (`wsl -u root -d NixOS` on the work box; the console or a serial/HDMI login
 elsewhere) and roll back with `nixos-rebuild switch --rollback`, or pick the
@@ -358,10 +350,10 @@ Claude to route new memories there.
 ## Per-host differences
 
 |                             | Personal Linux (sway) | macOS                 | Work WSL (EDaaS)            |
-| --------------------------- | --------------------- | --------------------- | ---------------------------- |
+| --------------------------- | --------------------- | --------------------- | --------------------------- |
 | Auto-tmux                   | yes (foot/TTY)        | yes (iTerm2)          | yes (WSL shell)             |
 | `kubectl` → kubecolor       | no (no kubectl)       | no                    | yes (work module)           |
-| `sudo` implementation       | sudo-rs (password)    | Apple sudo + Touch ID | sudo-rs (passwordless wheel) |
+| `sudo` implementation       | sudo-rs               | Apple sudo + Touch ID | sudo-rs                     |
 | git email                   | `iam@emmathe.dev`     | `iam@emmathe.dev`     | `…@citrix.com` (work)       |
 | ssh config managed          | yes                   | yes                   | no (keeps corporate config) |
 | ssh-agent                   | yes                   | launchd               | yes (work module)           |

flake.lock

@@ -3,16 +3,16 @@
     "brew-src": {
       "flake": false,
       "locked": {
-        "lastModified": 1786945682,
+        "lastModified": 1786348930,
-        "narHash": "sha256-VBESSoJccikdhxh3vp3SQeG7cZXTOulMvVkoSqNDEhs=",
+        "narHash": "sha256-bCQJkbgsAMDp5HQystZLCq11UHiyEuoWbxKulAPYrh8=",
         "owner": "Homebrew",
         "repo": "brew",
-        "rev": "5b90e281d4e0c8fbd6ca4d8358276fb305b8d0bd",
+        "rev": "3ecc9eff23feebf1bc73846d74e14a122c93b66f",
         "type": "github"
       },
       "original": {
         "owner": "Homebrew",
-        "ref": "6.0.18",
+        "ref": "6.0.16",
         "repo": "brew",
         "type": "github"
       }
@@ -25,11 +25,11 @@
       },
       "locked": {
         "dir": "pkgs/firefox-addons",
-        "lastModified": 1787457768,
+        "lastModified": 1786853140,
-        "narHash": "sha256-cbgeu5NTb6DtB+tNs4E6z6K/1XKKM90gVmlkWMJe+gY=",
+        "narHash": "sha256-O880FlUav75Q5aNlg9znyg/avf1X/W7o/cAtZFLtpWc=",
         "owner": "rycee",
         "repo": "nur-expressions",
-        "rev": "25cfc8fdc413d73b3a47e3e86dafcad51cf5c9f9",
+        "rev": "ba9568c9c0df6290dc2f34b032ab4cb575e73788",
         "type": "gitlab"
       },
       "original": {
@@ -135,11 +135,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1787424939,
+        "lastModified": 1784288435,
-        "narHash": "sha256-O2tBn84NNuHrnqNVxx/XqsXwfYvS1YwBh+7CBnbCYsk=",
+        "narHash": "sha256-ReRHaLgr/uVqdD8afFSn+myXIfpHeOhP0yYe0TJqAA8=",
         "owner": "cachix",
         "repo": "git-hooks.nix",
-        "rev": "809414f0cdadf82cf11b06c2b29ba9b3168b3297",
+        "rev": "43b3c1ab9d40fb1dbb008f451988a91e375825e9",
         "type": "github"
       },
       "original": {
@@ -155,11 +155,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1787377438,
+        "lastModified": 1786924861,
-        "narHash": "sha256-Sxu1NLTD/Ern6hFGLlZmtKCSct3YQXZI/lls8RE1XeM=",
+        "narHash": "sha256-hftabkb+73OcGzvwFAjCiQorAhprs9TnU1+FkGO5CIw=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "65258d5c65a250189fde2e35f490d15e064c4c62",
+        "rev": "09ae1b85a6db412d841d60f924b23f881f0d0a38",
         "type": "github"
       },
       "original": {
@@ -185,6 +185,26 @@
         "type": "github"
       }
     },
+    "legacy-email-proxy": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1787315211,
+        "narHash": "sha256-FuZ9nXMRtnMPO/wbjYkpsKn6K/FFc64P5XDmCyfyxGs=",
+        "ref": "refs/heads/main",
+        "rev": "f1e1373fd350fd77f1848eddfa67ed9e00724c25",
+        "revCount": 13,
+        "type": "git",
+        "url": "https://code.emmathe.dev/lyrathorpe/legacy-email-proxy"
+      },
+      "original": {
+        "type": "git",
+        "url": "https://code.emmathe.dev/lyrathorpe/legacy-email-proxy"
+      }
+    },
     "nix-darwin": {
       "inputs": {
         "nixpkgs": [
@@ -211,11 +231,11 @@
         "brew-src": "brew-src"
       },
       "locked": {
-        "lastModified": 1787330919,
+        "lastModified": 1786686423,
-        "narHash": "sha256-LslMncqN7uOOH5S88WZtO/EVt2HwD8ltUnfyANk+mC0=",
+        "narHash": "sha256-8q3WdB8o3VUI7rOz1OXfioXIaaWbFTAxRJAkWLlfc0s=",
         "owner": "zhaofengli",
         "repo": "nix-homebrew",
-        "rev": "b00218e4aec0e5bf07d61a0bb13f842faa582d7b",
+        "rev": "ccabf79a6b9845eb72b51ea1d9c7ce3446350df3",
         "type": "github"
       },
       "original": {
@@ -231,11 +251,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1787457452,
+        "lastModified": 1786852476,
-        "narHash": "sha256-FJh4esFS3zqNNuKwvN3t6wrJGewqp1AUF9DAEvoKPD8=",
+        "narHash": "sha256-IM5CYtf86W4w8eUPpKcY/LpdHElmVBtJhaKnoTKxZEA=",
         "owner": "nix-community",
         "repo": "nix-index-database",
-        "rev": "c51d5c2ba69c907a34e90c9b6b80cd2b93811745",
+        "rev": "c7962dc97b45129df8d751bedaf37beb5a17706e",
         "type": "github"
       },
       "original": {
@@ -272,11 +292,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1787144466,
+        "lastModified": 1786867632,
-        "narHash": "sha256-HHfv2/HkNSKbbSyU9iD/g8lbP6r4tl33sSw1W4rXCk0=",
+        "narHash": "sha256-ez+ubZlA1RtdjCB18a6zJ9M4u8qoPDy08EcnsW5M3Xw=",
         "owner": "NixOS",
         "repo": "nixos-hardware",
-        "rev": "0471accf8d0a8210b31d947497d179ecc99e0021",
+        "rev": "ff17823245ab9ff7bcae6acf950bd89cba82c38c",
         "type": "github"
       },
       "original": {
@@ -308,11 +328,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1787414105,
+        "lastModified": 1786711500,
-        "narHash": "sha256-WncT27+3BOkgTaJZLnCsf3LcYf9RXMuR9ONSN4rzQ7s=",
+        "narHash": "sha256-QvnceIGTBeDvDd9oCn+GvdsnkquliuwbVgpiRH68qaQ=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "a9e6d84f9c2f9012f5fe7d964a7851352300e61a",
+        "rev": "02e08985a27c65ffd33d434eeb2e660a2e4dc84d",
         "type": "github"
       },
       "original": {
@@ -324,11 +344,11 @@
     },
     "nixpkgs-unstable": {
       "locked": {
-        "lastModified": 1787360063,
+        "lastModified": 1786862985,
-        "narHash": "sha256-dt4WdcvsA8/RCe+VZZwqU0X+XMM3wBbGCWA0/sFWzGo=",
+        "narHash": "sha256-FBJRXmbGXiSUDvYEbfLYRkckayyZ6SK1UEqhCrIZ2Cs=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "2c423e03bbafcff28bfadc6781a4a8257f205cb5",
+        "rev": "e5bdc4a41d4c072fe1e3787eaa0320a384741d44",
         "type": "github"
       },
       "original": {
@@ -347,11 +367,11 @@
         "systems": "systems"
       },
       "locked": {
-        "lastModified": 1787536726,
+        "lastModified": 1786873773,
-        "narHash": "sha256-aBh5Yk9tX8ZV4k10BJr2fvTq0/+iWGegaCMUOU7YKas=",
+        "narHash": "sha256-Hj/nkhKDv0aJly1PAUstrhrgEYn1mVSkLIYMh90r/Pc=",
         "owner": "nix-community",
         "repo": "nixvim",
-        "rev": "e2c3f9f36326d07340626847543c557e2b95fb50",
+        "rev": "b397fb9f6950d57355d62bb92457d223464e0115",
         "type": "github"
       },
       "original": {
@@ -368,6 +388,7 @@
         "git-hooks": "git-hooks",
         "home-manager": "home-manager",
         "kube-tmux": "kube-tmux",
+        "legacy-email-proxy": "legacy-email-proxy",
         "nix-darwin": "nix-darwin",
         "nix-homebrew": "nix-homebrew",
         "nix-index-database": "nix-index-database",

flake.nix

@@ -67,6 +67,13 @@
       url = "github:jonmosco/kube-tmux";
       flake = false;
     };
+    # legacy-email-proxy: cleartext POP3/SMTP front end for the Psion's mail
+    # client, proxied to authenticated IMAPS/SMTPS. Ships its own package and
+    # NixOS module; the Pi Zero 2 W host just enables the service.
+    legacy-email-proxy = {
+      url = "git+https://code.emmathe.dev/lyrathorpe/legacy-email-proxy";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs =
@@ -327,6 +334,26 @@
               ./users/lyrathorpe/home.nix
             ];
           };
+
+          lyrathorpe-zero2w = {
+            system = "aarch64-linux";
+            portable = false;
+            # Headless "Psion sidecar": PPP over RS232 plus a legacy mail proxy
+            # (hosts/PiZero2W/). No sway.nix; the raspberry-pi-3 profile carries
+            # the kernel/firmware/device tree (the Zero 2 W is the Pi 3's
+            # BCM2837 SoC) and ssh.nix adds key-only sshd. This board has 512 MB
+            # of RAM and never builds its own system -- see
+            # docs/hosts/pizero2w.md.
+            modules = [
+              ./hosts/PiZero2W/configuration.nix
+              inputs.nixos-hardware.nixosModules.raspberry-pi-3
+              ./modules/ssh.nix
+            ];
+            users.lyrathorpe.homeModules = [
+              ./home
+              ./users/lyrathorpe/home.nix
+            ];
+          };
         };
 
         # Darwin host table — macOS machines built via mkDarwinHost. The shared
@@ -365,8 +392,24 @@
         # nixpkgs instance for that system. Outputs here become per-system
         # attrsets automatically (e.g. devShells.<system>.default).
         perSystem =
-          { config, pkgs, ... }:
           {
+            config,
+            pkgs,
+            system,
+            ...
+          }:
+          {
+            # One-shot SD card for bringing the Pi Zero 2 W up: that host's own
+            # configuration plus the sd-image module, so the first boot is
+            # already the real system. aarch64-linux only -- building it needs
+            # an aarch64 Linux builder. See docs/hosts/pizero2w.md.
+            packages = lib.optionalAttrs (system == "aarch64-linux") {
+              zero2w-sd-image =
+                ((mkHost hosts.lyrathorpe-zero2w).extendModules {
+                  modules = [ ./hosts/PiZero2W/sd-image.nix ];
+                }).config.system.build.sdImage;
+            };
+
             # treefmt drives `nix fmt` and the formatting check below. nixfmt
             # stays the .nix formatter (the tree is already nixfmt-formatted);
             # shfmt covers shell and prettier covers markdown/yaml/json.

home/claude/memory/MEMORY.md

@@ -15,5 +15,3 @@
 - [Dev clusters disposable](dev_clusters_disposable.md) — Lyra's dev clusters are recreatable; mutate/break freely, no confirmation needed
 - [Nix shell tooling](nix_shell_tooling.md) — any nixpkgs tool runs ad hoc via `nix run`/`nix shell nixpkgs#<pkg>`; a missing command is never a dead end
 - [WSP local build and test](wsp_local_build_and_test.md) — core-services-cloud on this box: dotnet via nix, artifactory creds from `~/.artifactoryenv` sourced per command, how to tell auth failure from a code failure
-- [WSP-32957 PIM migration](wsp_32957_pim_migration.md) — AKS RBAC to PIM + AutoPerm decommission; prod is in the Technical Preview subscription, three tenants; resume via `~/code/WSP-32957-CONTINUATION.md`
-- [Entra group member reads](entra_group_member_reads.md) — `az ad group member list` hides service principal members; use the servicePrincipal cast or transitiveMemberOf, and trust the Terraform plan over it

home/claude/memory/entra_group_member_reads.md

@@ -1,28 +0,0 @@
----
-name: entra-group-member-reads
-description: az ad group member list and Graph /members silently omit service principal members — use the servicePrincipal cast or transitiveMemberOf when a group is expected to hold an SPN.
-metadata:
-  node_type: memory
-  type: reference
----
-
-`az ad group member list --group <id>` and `GET /groups/{id}/members` both return an **empty collection**, with no error, for a group whose only members are service principals — at least when called with Lyra's user account. The read looks authoritative and is not.
-
-**Reliable reads instead:**
-
-```sh
-# members, cast to the type that is being hidden
-az rest --method get --url "https://graph.microsoft.com/v1.0/groups/<gid>/members/microsoft.graph.servicePrincipal?\$select=id,displayName"
-
-# count, which does not filter
-az rest --method get --url "https://graph.microsoft.com/v1.0/groups/<gid>/members/\$count" --headers ConsistencyLevel=eventual
-
-# from the principal's side
-az rest --method get --url "https://graph.microsoft.com/v1.0/servicePrincipals/<spid>/transitiveMemberOf?\$select=id,displayName"
-az rest --method post --url "https://graph.microsoft.com/v1.0/servicePrincipals/<spid>/checkMemberGroups" \
-  --body '{"groupIds":["<gid>"]}' --headers "Content-Type=application/json"
-```
-
-**How to apply:** any group that deployment or automation identities belong to — `*-cluster-admins`, `*-keyvault`, anything created by `rg-prereqs` — must be checked with one of the above before concluding it is empty. Cross-check against Terraform: a plan reporting "No changes" against a `members` attribute is strong evidence the membership is present, and outranks the `az` read. On 2026-08-28 the plain read produced a Bug (WSP-33432, cancelled) claiming five `*-cluster-admins` groups across three tenants had been emptied; all five held their deployment principals the whole time.
-
-Related: [[wsp-32957-pim-migration]].

home/claude/memory/jira_wsp_fields.md

@@ -9,9 +9,7 @@ Field map for the **WSP (Workspace Platform)** Jira project, to create tickets w
 
 **Issue-type IDs:** Epic `10000`, Story `10004`, Task `10008`, Bug `10123`, Sub-task `10009`.
 
-**Fast path — use Task, not Bug.** A `Task` requires `summary` plus **Task Type** `customfield_15622` (added since this note was first written; the create validator enforces it even though `createmeta` omits it, same trap as Bug's `versions`). Options value=id: Dev Task=34065, CQE Task=34066, Investigation=34067, Security=34068, Maintenance=34069, Release=34070 — use `Maintenance` for refactors and tidy-ups, `Dev Task` for feature work. A `Bug` requires six extra fields (below), so only pick Bug when it must be a Bug. The sibling infra/remediation tickets in WSP are Tasks.
+**Fast path — use Task, not Bug.** A `Task` requires only `summary` (project/issuetype auto, reporter defaults to caller). A `Bug` requires six extra fields (below), so only pick Bug when it must be a Bug. The sibling infra/remediation tickets in WSP are Tasks.
-
-Example Task `additional_fields`: `{"customfield_15622":{"id":"34069"},"components":[{"name":"Multicluster Platform"}]}`
 
 **Bug required fields** (enforced by the create validator; note `createmeta` omits `versions` but the API rejects without it):
 

home/claude/memory/wsp_32957_pim_migration.md

@@ -1,58 +0,0 @@
----
-name: wsp-32957-pim-migration
-description: State of the WSP AKS-RBAC-to-PIM migration and AutoPerm decommission, and how to resume it
-metadata:
-  node_type: memory
-  type: project
----
-
-Long-running epic (August 2026) moving WSP's AKS cluster RBAC off **AutoPerm
-Manager**-maintained `wsp-*` groups onto the per-subscription **`CEO-*` Azure PIM**
-groups, then retiring AutoPerm. Epic **WSP-32957**; on the critical path for Zensar
-L1 on-call (WSP-32193). Work happens in **`~/code/multicluster`**
-(`terraform/cluster`, `terraform/cluster-k8s-resources`, `products/*/environments/*`).
-
-**Resume from `~/code/WSP-32957-CONTINUATION.md`** — full state, branch list,
-verified object IDs, findings and next steps. Jira is the durable record; that file
-is the index. Keep it updated as work lands ([[docs-keep-updated]]).
-
-**Landed:** WSP-33141 (multicluster PR #1808, merged `b047163c`) added object-ID
-inputs — `admin_group_oids` on `cluster`, and `cluster_user_group_oids` /
-`cluster_viewer_group_oids` / `cluster_superuser_group_oids` on
-`cluster-k8s-resources`. Supplying IDs _replaces_ the display-name lookup and leaves
-the `data "azuread_group"` unread, which is what will let the legacy groups be
-deleted. Nothing sets them yet, so behaviour is unchanged. Repoint branches for test
-(WSP-33067) and staging (WSP-33068) are pushed but have **no PR** — both gated on
-decisions, not code.
-
-**Facts that cost real effort to establish, do not re-derive:**
-
-- **Production runs in `fc7af6ae-…` (_Workspace Platform Technical Preview_), not
-  `d6d75d07-…` (_Workspace Platform Production_)**, which holds no clusters. The
-  epic was wrong about this for its whole life and every production `CEO-*` group
-  name and object ID had to change. Because `CEO-*` names embed the subscription
-  name, **always re-verify object IDs against live Entra rather than trusting the
-  epic table.**
-- **Three tenants**, not two: `6f4fe054` (prod, prod JP), `335836de` (staging,
-  staging JP, test), `3eae2746` (dev). Each `wsp-*` name is a distinct object in
-  each tenant.
-- `wsp-staging-cluster-admins` and `wsp-test-cluster-admins` are **empty**, so
-  `wsp-owner` is the _only_ path to `cluster-admin` in staging. Never drop it before
-  `SuperAdmin-*` is proven — hence the staging branch is split into an additive
-  commit and a cutover commit.
-- **No break-glass exists**: `disableLocalAccounts = True` on every cluster; only the
-  deployment SPNs authenticate non-interactively.
-- Graph **PIM-for-Groups is unreadable via `az`** (the CLI's first-party client lacks
-  `PrivilegedAccess.Read.AzureADGroup`, on both `v1.0` and `beta`). Use the portal or
-  `Connect-MgGraph -Scopes PrivilegedAccess.Read.AzureADGroup`.
-
-**Watch for:** the epic gets rewritten by James Weldrake between sessions — re-read
-the description before acting, and check which child tickets are still live
-(WSP-33062/33063/33064/33066 were cancelled 2026-08-24, and dev was put out of
-scope). Verified findings have repeatedly contradicted the epic text
-([[copilot-review-false-positives]] is the same instinct: check against reality
-first).
-
-Queued Slack messages and the leaver report live as `~/code/*.txt` alongside the
-continuation file; see the table in it for what has and has not been sent
-([[workflow-review-and-comments]] — show them before they go out).

home/shell.nix

@@ -287,22 +287,7 @@ in
     plugins = with pkgs.tmuxPlugins; [
       sensible
       vim-tmux-navigator # Ctrl-h/j/k/l across vim splits and tmux panes
-      {
+      yank
-        # On WSL, tmux-yank pipes the selection to clip.exe, which decodes its
-        # stdin as the OEM codepage instead of UTF-8 -- an em dash reaches the
-        # Windows clipboard as three characters. Route through tmux's own
-        # buffer instead: with set-clipboard on, tmux emits OSC 52 and the
-        # terminal takes the text as UTF-8. Windows Terminal honours OSC 52;
-        # iTerm2 does not by default, hence the runtime guard rather than
-        # overriding pbcopy/xsel on every host. yank.tmux bakes the command
-        # into its key bindings when it loads, so this must be set first, which
-        # is what plugin extraConfig gives us.
-        plugin = yank;
-        extraConfig = ''
-          if-shell 'grep -qi microsoft /proc/version 2>/dev/null' \
-            "set -g @override_copy_command 'tmux load-buffer -w -'"
-        '';
-      }
       extrakto # prefix+Tab: fzf-grab paths/URLs/text from the pane into the prompt
       {
         # Catppuccin Mocha statusline (v2 API: flavour + window options must be
@@ -313,14 +298,6 @@ in
         extraConfig = ''
           set -g @catppuccin_flavor 'mocha'
           set -g @catppuccin_window_status_style 'rounded'
-          # Catppuccin's default window text is #T, the pane title, which every
-          # program in the pane is free to overwrite -- the shell writes the
-          # hostname, Claude Code writes its current task, and a hand-set window
-          # name never appears. Show the window name instead, falling back to the
-          # pane title when the window holds a single pane and the two carry the
-          # same information anyway.
-          set -g @catppuccin_window_text ' #{?#{==:#{window_panes},1},#T,#W}'
-          set -g @catppuccin_window_current_text ' #{?#{==:#{window_panes},1},#T,#W}'
         '';
       }
       resurrect # save/restore sessions
@@ -365,17 +342,6 @@ in
       set -g renumber-windows on
       set -g set-clipboard on
 
-      # Pane titles on the border, but only once a window is split -- a single
-      # pane's title is already in the status bar. pane-border-status takes no
-      # format, so the hook recomputes it whenever the layout changes, which
-      # covers both splitting and closing a pane.
-      set -g pane-border-format " #P #{pane_title} "
-      set -g pane-border-status off
-      set-hook -g window-layout-changed 'set -Fw pane-border-status "#{?#{>:#{window_panes},1},top,off}"'
-
-      # Pane titles have no default binding.
-      bind T command-prompt -p "pane title:" "select-pane -T '%%'"
-
       # Catppuccin v2 statusline. Must run after the plugin has loaded;
       # home-manager appends this extraConfig after the whole plugin list.
       set -g status-left-length 100

hosts/Darwin/configuration.nix

@@ -161,11 +161,6 @@
     dock = {
       show-recents = false;
       mru-spaces = false; # don't reorder spaces by use
-      # Disable hot-corners
-      wvous-tr-corner = 1;
-      wvous-tl-corner = 1;
-      wvous-bl-corner = 1;
-      wvous-br-corner = 1;
     };
     finder = {
       AppleShowAllExtensions = true;

hosts/EDaaS/configuration.nix

@@ -60,11 +60,6 @@
   ## patch the script
   systemd.services.docker-desktop-proxy.script = lib.mkForce ''${config.wsl.wslConf.automount.root}/wsl/docker-desktop/docker-desktop-user-distro proxy --docker-desktop-root ${config.wsl.wslConf.automount.root}/wsl/docker-desktop "C:\Program Files\Docker\Docker\resources"'';
 
-  # NixOS-WSL's passwordless wheel default only covers `security.sudo`; the
-  # sudo-rs swap in common-nixos.nix needs it set again. No console login here,
-  # and no account password anyone knows.
-  security.sudo-rs.wheelNeedsPassword = false;
-
   features.swayDesktop.enable = false;
 
   # NOTE: this user's systemd --user lingering -- so the home-manager renovate

hosts/PiZero2W/configuration.nix

@@ -0,0 +1,111 @@
+# Raspberry Pi Zero 2 W (aarch64) "Psion sidecar": an RS232 companion for a
+# Psion 5MX. Two roles, split into submodules: ./serial-ppp.nix (PPP over the
+# serial line, NAT out to wifi, telnet login) and ./email-proxy.nix (cleartext
+# POP3/SMTP front end for the Psion's mail client). The raspberry-pi-3
+# nixos-hardware profile (the Zero 2 W is the same BCM2837 SoC as the Pi 3) and
+# key-only sshd (../../modules/ssh.nix) are layered on in the flake host table.
+# Install notes: see ../../docs/hosts/pizero2w.md.
+{ lib, ... }:
+{
+  imports = [
+    ./hardware-configuration.nix
+    ./serial-ppp.nix
+    ./email-proxy.nix
+  ];
+
+  # Match the flake's nixosConfigurations attribute name so `nh os switch`
+  # (which selects by the local hostname) resolves without an explicit -H flag.
+  networking.hostName = "lyrathorpe-zero2w";
+
+  # Headless server: modules/sway.nix is not imported and
+  # features.swayDesktop.enable defaults to false, so this host keeps plain
+  # TTY/SSH login.
+
+  # Claude Code is a Node application. It runs on aarch64, but not usefully in
+  # 512 MB of RAM, and its closure is unwelcome on an SD card.
+  features.claudeCode.enable = false;
+
+  # 512 MB total and no swap partition -- SD cards wear out under swap writes.
+  # Compressed RAM swap instead; zstd is the best ratio-per-cycle the SoC can
+  # sustain.
+  zramSwap = {
+    enable = true;
+    algorithm = "zstd";
+  };
+
+  # The NixOS manual and man page index cost build time and a chunk of the card
+  # for a box that is administered over SSH from elsewhere.
+  documentation.nixos.enable = false;
+
+  # Own the firmware partition declaratively: every switch rewrites config.txt,
+  # the vendor device trees and the overlays below. Without this the card keeps
+  # whatever config.txt the flashed image wrote and the UART overlays never
+  # load. uboot.enable keeps the GPU firmware chainloading U-Boot -> extlinux,
+  # which is how the NixOS aarch64 SD image boots; leaving it off would rewrite
+  # config.txt without a `kernel=` line and the board would stop booting.
+  hardware.raspberry-pi.firmware = {
+    enable = true;
+    uboot.enable = true;
+  };
+
+  hardware.raspberry-pi.configtxt = {
+    settings.all = {
+      # Headless: hand the VideoCore the minimum and leave the rest to Linux.
+      # start_x/camera_auto_detect otherwise reserve VRAM for a camera stack
+      # this board does not have.
+      gpu_mem = 16;
+      start_x = 0;
+      camera_auto_detect = false;
+      # Left on, the firmware auto-loads the KMS display overlay, which wants
+      # more VRAM than this board can spare for a monitor it will never have.
+      display_auto_detect = false;
+    };
+
+    # Replaces the profile's default (vc4-kms-v3d), which is display hardware
+    # this host never uses.
+    deviceTreeOverlays.all = [
+      # Move the PL011 UART off Bluetooth and onto GPIO 14/15, so /dev/ttyAMA0
+      # is the RS232 header. The mini UART (ttyS0) derives its baud rate from
+      # the core clock and drifts at 115200.
+      { disable-bt = { }; }
+      # RTS/CTS on GPIO 16/17: the Psion's modem profile uses hardware flow
+      # control, and so does pppd in ./serial-ppp.nix.
+      { uart0.ctsrts = true; }
+    ];
+  };
+
+  # Wifi is the Pi's uplink and the route the Psion reaches the internet over
+  # (./serial-ppp.nix masquerades onto it).
+  networking.interfaces.wlan0.useDHCP = true;
+  networking.wireless = {
+    enable = true;
+    interfaces = [ "wlan0" ];
+    # PSKs stay out of the Nix store: wpa_supplicant reads them at runtime from
+    # this file, which is created on the device (root-owned, 0600) and contains
+    #   psk_home=<the pre-shared key>
+    # See ../../docs/hosts/pizero2w.md.
+    secretsFile = "/var/lib/wpa_supplicant/secrets.conf";
+    networks."CHANGE-ME-SSID".pskRaw = "ext:psk_home";
+  };
+
+  # The board takes a DHCP lease over wifi, so its address moves. mDNS makes it
+  # findable as lyrathorpe-zero2w.local instead of hunting through the router's
+  # lease table -- which matters most on first boot, when it is the only way in.
+  services.avahi = {
+    enable = true;
+    openFirewall = true;
+    publish = {
+      enable = true;
+      addresses = true;
+      workstation = true;
+    };
+  };
+
+  # Default-deny inbound. sshd opens 22 (../../modules/ssh.nix); everything the
+  # Psion talks to is reached over the PPP link, which ./serial-ppp.nix marks
+  # trusted.
+  networking.firewall.enable = true;
+
+  # See `man configuration.nix` / the stateVersion docs before changing.
+  system.stateVersion = "26.05";
+}

hosts/PiZero2W/email-proxy.nix

@@ -0,0 +1,25 @@
+# legacy-email-proxy: a cleartext POP3 (110) and SMTP (25) front end for the
+# Psion's built-in mail client, forwarded to authenticated IMAPS/SMTPS.
+#
+# The package, the systemd unit and its hardening all live upstream
+# (https://code.emmathe.dev/lyrathorpe/legacy-email-proxy); this host only
+# enables the service and points it at the credentials.
+{ inputs, ... }:
+{
+  imports = [ inputs.legacy-email-proxy.nixosModules.default ];
+
+  services.legacy-email-proxy = {
+    enable = true;
+
+    # The listeners are unauthenticated and unencrypted by design, so the
+    # firewall is what confines them: ppp0 is trusted, wlan0 is not, and 110/25
+    # are never opened there (./serial-ppp.nix). They stay on the default
+    # 0.0.0.0 rather than the PPP address because 10.0.0.1 exists only while
+    # the Psion is plugged in, and a bind-time dependency on a serial cable is
+    # a restart loop waiting to happen.
+
+    # Backend hostnames and credentials. Kept out of the Nix store: created on
+    # the device, root-owned 0600. See ../../docs/hosts/pizero2w.md.
+    environmentFile = "/var/lib/legacy-email-proxy/backend.env";
+  };
+}

hosts/PiZero2W/hardware-configuration.nix

@@ -0,0 +1,33 @@
+# PLACEHOLDER hardware configuration for the Raspberry Pi Zero 2 W.
+#
+# This file is NOT the real generated config -- it exists only so the host
+# evaluates in CI before the Pi is provisioned. The machine will not boot from
+# it as-is. On first install, regenerate this file on the device with
+#   nixos-generate-config --root /mnt
+# and replace this placeholder with the output (commit it). See ../../docs/hosts/pizero2w.md.
+#
+# Like every hardware-configuration.nix in this repo, this file is excluded from
+# the formatter and linters (see the pre-commit/treefmt excludes in flake.nix).
+{ modulesPath, ... }:
+{
+  imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+
+  nixpkgs.hostPlatform = "aarch64-linux";
+
+  # The Zero 2 W boots from an SD card with a FAT firmware partition and an ext4
+  # root. Labels match the conventional sd-image layout; the real generated
+  # config will use by-uuid device paths instead.
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/NIXOS_SD";
+    fsType = "ext4";
+  };
+
+  fileSystems."/boot/firmware" = {
+    device = "/dev/disk/by-label/FIRMWARE";
+    fsType = "vfat";
+  };
+
+  # 512 MB of RAM and an SD card: no swap partition (SD cards wear out under
+  # swap writes). zram takes its place; see ../../hosts/PiZero2W/configuration.nix.
+  swapDevices = [ ];
+}

hosts/PiZero2W/sd-image.nix

@@ -0,0 +1,44 @@
+# SD-card image of this host, used exactly once: to bring the board up.
+#
+# Deliberately NOT imported by ./configuration.nix. The flake extends the host
+# with it (see packages.aarch64-linux.zero2w-sd-image in ../../flake.nix), so
+# the card carries the host's own kernel, config.txt and SSH keys rather than a
+# generic installer that then has to be reconfigured over a console this host
+# does not have -- pppd owns the serial port (./serial-ppp.nix).
+#
+# It does not carry the runtime secrets. Seed those into the card's root
+# partition before first boot; see ../../docs/hosts/pizero2w.md.
+{
+  config,
+  lib,
+  modulesPath,
+  ...
+}:
+{
+  imports = [ "${modulesPath}/installer/sd-card/sd-image.nix" ];
+
+  # sd-image.nix pulls in profiles/all-hardware.nix, which is every driver and
+  # firmware blob NixOS knows about. The raspberry-pi-3 profile already carries
+  # what this board has, and the card is small.
+  hardware.enableAllHardware = lib.mkForce false;
+
+  image.baseName = "nixos-zero2w";
+
+  sdImage = {
+    # Compressing costs a long single-threaded pass and buys nothing: the image
+    # is written straight to a card with dd.
+    compressImage = false;
+
+    # The default 30 MiB does not hold the vendor GPU firmware, U-Boot and the
+    # BCM2837 device trees and overlays that nixos-hardware installs here.
+    firmwareSize = 128;
+
+    # The firmware partition is populated by nixos-hardware's firmware module
+    # (it takes over sdImage.populateFirmwareCommands); the root side is the
+    # stock extlinux install, which no longer arrives with it.
+    populateRootCommands = ''
+      mkdir -p ./files/boot
+      ${config.boot.loader.generic-extlinux-compatible.populateCmd} -c ${config.system.build.toplevel} -d ./files/boot
+    '';
+  };
+}

hosts/PiZero2W/serial-ppp.nix

@@ -0,0 +1,89 @@
+# The serial half of the Psion sidecar: a PPP link to a Psion 5MX over
+# /dev/ttyAMA0 (RS232 level shifter on the GPIO header, 115200 8N1 with
+# RTS/CTS), masqueraded out of wifi, plus a telnet login for the Psion's
+# terminal client.
+#
+# Cleartext telnet and unauthenticated PPP are safe *only* because the link is
+# a two-node cable: the peer is a machine from 1999 that speaks no TLS. Nothing
+# here is exposed to wlan0.
+{ pkgs, ... }:
+let
+  # Point-to-point addresses for the serial link; nothing else routes here.
+  piAddress = "10.0.0.1";
+  psionAddress = "10.0.0.2";
+in
+{
+  # pppd needs exclusive use of the port. NixOS starts a getty on any serial
+  # console named in boot.kernelParams; ttyAMA0 is not one today, but disable it
+  # explicitly so a later kernel-param change cannot silently steal the line.
+  systemd.services."serial-getty@ttyAMA0".enable = false;
+
+  services.pppd = {
+    enable = true;
+    peers.psion.config = ''
+      /dev/ttyAMA0
+      115200
+      ${piAddress}:${psionAddress}
+
+      # Hardware flow control, matching the Psion's modem profile.
+      crtscts
+
+      # A null-modem cable has no carrier detect and no peer to authenticate.
+      local
+      noauth
+
+      # The systemd unit is Type=notify, so pppd must stay in the foreground.
+      nodetach
+      lock
+
+      # Wait for the Psion rather than failing when it is unplugged, and keep
+      # waiting for the next time it is plugged back in.
+      passive
+      persist
+      maxfail 0
+      holdoff 1
+
+      # Hand the Psion resolvers over the link, so its Internet profile can set
+      # "get DNS from server = True" instead of hard-coding them.
+      ms-dns 1.1.1.1
+      ms-dns 8.8.8.8
+    '';
+  };
+
+  # The Psion's route to the internet. The original write-up used pppd's
+  # proxyarp instead; NAT keeps the Psion out of the LAN broadcast domain and
+  # does not depend on what the wifi router tolerates.
+  networking.nat = {
+    enable = true;
+    externalInterface = "wlan0";
+    internalIPs = [ "${psionAddress}/32" ];
+  };
+
+  # Everything the Psion connects to (telnet here, POP3/SMTP in
+  # ./email-proxy.nix) is reachable over the PPP link and nowhere else.
+  networking.firewall.trustedInterfaces = [ "ppp0" ];
+
+  # The Psion's terminal client speaks telnet over TCP, which it renders far
+  # better than the raw serial console. Socket-activated, one process per
+  # connection; busybox's telnetd in inetd mode hands straight over to login.
+  systemd.sockets.telnetd = {
+    description = "Telnet login socket for the Psion";
+    wantedBy = [ "sockets.target" ];
+    listenStreams = [ "${piAddress}:23" ];
+    socketConfig = {
+      Accept = true;
+      # ppp0 (and with it 10.0.0.1) only exists while the Psion is connected;
+      # FreeBind lets the socket be listening before that.
+      FreeBind = true;
+    };
+  };
+
+  systemd.services."telnetd@" = {
+    description = "Telnet login for the Psion";
+    serviceConfig = {
+      ExecStart = "-${pkgs.busybox}/bin/busybox telnetd -i -l ${pkgs.shadow}/bin/login";
+      StandardInput = "socket";
+      StandardError = "journal";
+    };
+  };
+}

hosts/RPi5/configuration.nix

@@ -17,7 +17,7 @@
 
   # Headless server: the Sway desktop is intentionally not set up. modules/sway.nix is
   # not imported and features.swayDesktop.enable defaults to false (declared in
-  # modules/features.nix), so this host keeps plain TTY/SSH login.
+  # system/modules/features.nix), so this host keeps plain TTY/SSH login.
 
   # Raspberry Pi boots via U-Boot + extlinux, not GRUB/systemd-boot. The
   # raspberry-pi-5 nixos-hardware profile supplies the kernel, firmware and

modules/sway.nix

@@ -12,7 +12,7 @@ let
 in
 {
   # The features.swayDesktop.enable option is declared in
-  # modules/features.nix (so headless hosts can read/set it without
+  # system/modules/features.nix (so headless hosts can read/set it without
   # importing this module). This module only provides its implementation.
   config = lib.mkIf cfg.enable {
     programs.sway = {

modules/users.nix

@@ -29,10 +29,10 @@
     // lib.optionalAttrs (spec ? linger) { inherit (spec) linger; }
   ) hostUsers;
 
-  programs.firefox = lib.mkIf config.features.swayDesktop.enable {
+  programs.firefox = lib.mkIf (config.features.swayDesktop.enable == true) {
     enable = true;
   };
-  programs.thunderbird = lib.mkIf config.features.swayDesktop.enable {
+  programs.thunderbird = lib.mkIf (config.features.swayDesktop.enable == true) {
     enable = true;
   };
 }

users/emmathorpe/work.nix

@@ -47,23 +47,7 @@
     pkgs.terraform-docs # generate Terraform module docs
     pkgs.yq-go # jq for YAML
     pkgs.gcx # Grafana Cloud CLI (dashboards, SLOs, synthetics, alerts)
-
-    # WSL ships no xdg-open, so anything that shells out to a browser dies with
-    # `exec: "xdg-open,x-www-browser,www-browser": executable file not found`.
-    # kubelogin's interactive login is the one that bites: it is the login mode
-    # the shared cluster kubeconfig uses. Hand the URL to Windows instead.
-    # (wslu, the usual answer, is gone from nixpkgs -- upstream archived it.)
-    (pkgs.writeShellScriptBin "xdg-open" ''
-      url="$1"
-      if command -v powershell.exe >/dev/null 2>&1; then
-        exec powershell.exe -NoProfile -Command "Start-Process '$url'"
-      fi
-      exec explorer.exe "$url"
-    '')
   ];
-
-  # Honoured by tools that read $BROWSER rather than calling xdg-open.
-  home.sessionVariables.BROWSER = "xdg-open";
   services.ssh-agent.enable = true;
 
   # Colourised kubectl. enableAlias points `kubectl` at kubecolor, which parses