fix(keyboard): isolate new-keyboard layout to its own device

The interactive new-keyboard picker applied the chosen layout with
`hyprctl switchxkblayout <device> <index>`, which flips the *shared*
layout for every keyboard without its own per-device config — so picking
a layout for an external board dragged the built-in keyboard along, and
the change stuck after unplug (it's global state, not device-bound).
Compounding it, the candidate `keyboard.layouts` pool was merged into
`input.kb_layout`, loading those layouts onto the session keyboard too.

Apply the choice as a per-device `hyprctl keyword device[<name>]:kb_layout`
instead — the runtime twin of the declarative `keyboard.devices` blocks —
so it isolates that one keyboard and never touches the built-in board.
Keep the candidate pool out of `input.kb_layout` (session keyboard carries
only `keyboard.layout`); the pool is for external boards, applied per-device.

Also put `nomarchy-keyboard-watch` on PATH when enabled (it was store-path
only via exec-once, so undiscoverable) for debugging.

Found on the Latitude 5410 hardware sweep; picker itself verified working.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home/hyprland.nix

@@ -55,10 +55,14 @@ let
       ++ lib.optional (m.extra != "") m.extra
     );
 
-  # Keyboard layout candidates: the primary nomarchy.keyboard.layout (split on
-  # commas) plus any nomarchy.keyboard.layouts. Drives input.kb_layout so all
-  # of them are switchable, and feeds the watcher's picker.
-  kbLayouts = lib.unique (
+  # Candidate layouts offered by the new-keyboard picker: the session
+  # layout(s) (nomarchy.keyboard.layout, comma-split for a multi-layout
+  # session) plus the extra nomarchy.keyboard.layouts pool. The pool is
+  # deliberately NOT merged into input.kb_layout — those candidates are for
+  # *external* keyboards and get applied per-device by the watcher's apply().
+  # Loading them onto the session keyboard is what let a global switch flip
+  # the built-in board to the wrong layout.
+  pickerLayouts = lib.unique (
     (lib.splitString "," config.nomarchy.keyboard.layout)
     ++ config.nomarchy.keyboard.layouts
   );
@@ -68,18 +72,20 @@ let
   # keyboard.devices, not already remembered), ask for a layout and persist it
   # per-device, re-applying silently on later reconnects. Stateful runtime
   # piece — the complement to the declarative keyboard.devices. Reliable
-  # primitives only: poll hyprctl devices, apply via switchxkblayout (an index
-  # into kbLayouts). NOTE: needs an on-hardware test (hotplug isn't verifiable
-  # in CI).
+  # primitives only: poll hyprctl devices, apply with a per-device
+  # `device[<name>]:kb_layout` keyword — the runtime twin of the declarative
+  # device blocks, so it isolates that one keyboard and never disturbs the
+  # built-in board (switchxkblayout flipped the *shared* layout, which leaked
+  # onto the laptop and stuck after unplug). NOTE: needs an on-hardware test
+  # (hotplug isn't verifiable in CI).
   keyboardWatch = pkgs.writeShellScriptBin "nomarchy-keyboard-watch" ''
     set -u
-    layouts="${lib.concatStringsSep " " kbLayouts}"
+    layouts="${lib.concatStringsSep " " pickerLayouts}"
     declared="${lib.concatStringsSep " " (builtins.attrNames config.nomarchy.keyboard.devices)}"
     state="''${XDG_STATE_HOME:-$HOME/.local/state}/nomarchy/keyboard-layouts"
     mkdir -p "$(dirname "$state")"; [ -f "$state" ] || : > "$state"
 
-    layout_index() { i=0; for l in $layouts; do [ "$l" = "$1" ] && { printf %s "$i"; return; }; i=$((i + 1)); done; printf %s -1; }
-    apply() { idx=$(layout_index "$2"); [ "$idx" -ge 0 ] && hyprctl switchxkblayout "$1" "$idx" >/dev/null 2>&1; }
+    apply() { hyprctl keyword "device[$1]:kb_layout" "$2" >/dev/null 2>&1; }
     keyboards() { hyprctl devices -j | jq -r '.keyboards[].name'; }
     is_declared() { case " $declared " in *" $1 "*) return 0 ;; *) return 1 ;; esac; }
     saved_for() { while IFS='=' read -r k v; do [ "$k" = "$1" ] && { printf '%s' "$v"; return; }; done < "$state"; }
@@ -201,8 +207,10 @@ in
 
       input = {
         # kb_layout/variant come from nomarchy.keyboard.* — set that
-        # option (the installer writes it; it also drives tty/LUKS).
-        kb_layout = lib.concatStringsSep "," kbLayouts;
+        # option (the installer writes it; it also drives tty/LUKS). Only the
+        # session layout(s) land here; the keyboard.layouts pool is applied
+        # per-device to external boards, never onto the session keyboard.
+        kb_layout = config.nomarchy.keyboard.layout;
         kb_variant = config.nomarchy.keyboard.variant;
         follow_mouse = lib.mkDefault 1;
         touchpad.natural_scroll = lib.mkDefault true;
@@ -270,7 +278,10 @@ in
   # writes a config file). A helper to find values for nomarchy.monitors —
   # the declarative config stays the source of truth (we don't source its
   # output). Gated on its toggle; pointless without the Hyprland session.
-  home.packages = lib.optionals
-    (config.nomarchy.hyprland.enable && config.nomarchy.displays.enable)
-    [ pkgs.nwg-displays ];
+  home.packages =
+    lib.optionals (config.nomarchy.hyprland.enable && config.nomarchy.displays.enable)
+      [ pkgs.nwg-displays ]
+    # The new-keyboard watcher on PATH (when enabled) so it's discoverable and
+    # runnable by name for debugging — Hyprland still exec-once's it by store path.
+    ++ lib.optional (config.nomarchy.hyprland.enable && kbAutoSwitch) keyboardWatch;
 }

modules/home/options.nix

@@ -105,10 +105,11 @@ in
         picker. When non-empty, a small watcher runs in the session: when a
         keyboard connects that isn't covered by nomarchy.keyboard.devices and
         hasn't been chosen before, it pops a rofi picker (these layouts plus
-        the primary nomarchy.keyboard.layout), applies the choice, and
-        remembers it per-device (~/.local/state) — re-applying automatically
-        on later reconnects. The runtime-remember complement to the
-        declarative keyboard.devices; a stateful runtime piece by design.
+        the primary nomarchy.keyboard.layout), applies the choice to that
+        keyboard only (a per-device kb_layout, so the built-in board is left
+        alone), and remembers it per-device (~/.local/state) — re-applying
+        automatically on later reconnects. The runtime-remember complement to
+        the declarative keyboard.devices; a stateful runtime piece by design.
       '';
     };