server: auto-create tank ZFS pool on first boot if data disk is blank

A fresh proxmox-server deploy has a blank scsi1 disk, so
zfs-import-tank.service spun 60 s then failed with no pool found.
Add zfs-init-tank.service that runs before the import: exits immediately
if the pool already exists, imports it if it exists but isn't imported
yet, or creates it on /dev/disk/by-id/scsi-*drive-scsi1 (Proxmox's
virtio-scsi naming for the second disk) with all required NFS datasets
if the disk is blank.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/nixos/home.nix

@@ -20,6 +20,7 @@
       #    vscode
       chromium
       claude-code
+      fish
     ];
 
     # Optional: set environment vars

modules/build-types/server.nix

@@ -1,12 +1,74 @@
-{ vars, lib, ... }:
+{ vars, lib, pkgs, ... }:
 
+let
+  poolName = lib.removePrefix "/" vars.storageRoot;
+
+  # For each NFS share subpath, generate every ancestor path so ZFS datasets
+  # are created parent-first.  e.g. "docker/config" → ["docker" "docker/config"]
+  ancestors = path:
+    let parts = lib.splitString "/" path;
+    in lib.imap1 (i: _: lib.concatStringsSep "/" (lib.take i parts)) parts;
+
+  poolDatasets = lib.unique (
+    lib.concatMap (share: ancestors share.subpath) (lib.attrValues vars.nfsShares)
+  );
+in
 {
   imports = [
     ../beszel/enable-agent.nix
     ../services/zfs/enable-service.nix
   ];
 
-  boot.zfs.extraPools = [ (lib.removePrefix "/" vars.storageRoot) ];
+  boot.zfs.extraPools = [ poolName ];
+
+  # On a fresh image deploy the data disk (scsi1) starts blank — no pool
+  # exists yet, so zfs-import-tank.service would spin for 60 s and fail.
+  # This service runs first: if the pool is already present it exits instantly;
+  # otherwise it creates it (with all required datasets) so the standard
+  # import service finds it ready on the very first boot.
+  systemd.services."zfs-init-${poolName}" = {
+    description = "Initialize '${poolName}' ZFS pool on first boot if not present";
+    wantedBy = [ "zfs-import-${poolName}.service" ];
+    before = [ "zfs-import-${poolName}.service" ];
+    after = [ "systemd-udev-settle.service" ];
+    unitConfig.DefaultDependencies = false;
+    serviceConfig = {
+      Type = "oneshot";
+      RemainAfterExit = true;
+    };
+    path = [ pkgs.zfs_unstable ];
+    script = ''
+      # Already imported — nothing to do.
+      if zpool list "${poolName}" >/dev/null 2>&1; then
+        exit 0
+      fi
+
+      # Pool exists on a device but not yet imported — let the standard
+      # zfs-import-${poolName}.service handle it normally.
+      if zpool import -d /dev/disk/by-id -N "${poolName}" 2>/dev/null; then
+        exit 0
+      fi
+
+      # No pool found at all.  Create it on the Proxmox data disk (scsi1),
+      # which appears as /dev/disk/by-id/scsi-*drive-scsi1 inside the VM.
+      DATA_DISK=""
+      for candidate in /dev/disk/by-id/scsi-*drive-scsi1; do
+        [[ "$candidate" == *-part* ]] && continue
+        [ -b "$candidate" ] && DATA_DISK="$candidate" && break
+      done
+
+      if [ -z "$DATA_DISK" ]; then
+        echo "zfs-init-${poolName}: no data disk found (expected /dev/disk/by-id/scsi-*drive-scsi1)" >&2
+        exit 1
+      fi
+
+      echo "zfs-init-${poolName}: creating pool on $DATA_DISK"
+      zpool create -f "${poolName}" "$DATA_DISK"
+      ${lib.concatMapStrings (ds: ''
+        zfs create "${poolName}/${ds}"
+      '') poolDatasets}
+    '';
+  };
 
   systemd.services.nfs-server = {
     after = [ "zfs-mount.service" ];