feat(displays): hotplug auto-switch for display profiles (item 15b)

nomarchy-display-profile gains `match <outputs>`: an exact set match
wins, else the largest profile whose named outputs are all connected;
any tie prints nothing — the watcher must never flap between ambiguous
layouts. nomarchy-display-profile-watch (exec-once when profiles are
declared, the keyboard-watcher poll pattern — session units race
Hyprland IPC on relogin) reacts to output-set CHANGES only, reads
settings.displayProfileAuto from the live state each time (the menu's
new Auto-switch row toggles it instantly, no rebuild), and applies via
the tool — so an auto-pick persists a concrete profile that the next
rebuild bakes. A separate boolean rather than an "auto" pseudo-profile
for exactly that bake semantics.

Verified: V0 (flake check); V1 — a scratch 4-profile downstream builds;
tool + watcher pass bash -n; the match matrix exercised end-to-end:
three exact picks, an unambiguous-superset pick, a tie -> none, a
no-fit -> none; the watcher is exec-once'd in the rendered config; the
menu renders the Auto-switch row. Remains: V3 real dock/undock
(HARDWARE-QUEUE, rides the slice-a entry). Slice c (workspace binding)
stays, tagged optional.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/home/hyprland.nix

@@ -94,12 +94,73 @@ ${lib.concatStringsSep "\n" (lib.mapAttrsToList
         ${sync} --quiet set settings.displayProfile "" --no-switch
         hyprctl reload >/dev/null 2>&1
         notify-send "Display profile" "Base layout restored." ;;
+      match)
+        # Which profile fits these connected outputs? (args = output names,
+        # e.g. `match $(hyprctl monitors all -j | jq -r '.[].name')`.)
+        # An exact set match wins; else the largest profile whose named
+        # outputs are all connected; any tie prints nothing (exit 1) — the
+        # auto-switch watcher must never flap between ambiguous layouts.
+        shift
+        [ "$#" -gt 0 ] || exit 1
+        con=" $* " ncon=$#
+        exact= exactdup= best= bestn=0 dup=
+        while IFS=: read -r p names; do
+          [ -n "$p" ] || continue
+          n=0 ok=1
+          for o in $names; do
+            case "$con" in *" $o "*) n=$((n+1)) ;; *) ok=; break ;; esac
+          done
+          [ -n "$ok" ] || continue
+          if [ "$n" -eq "$ncon" ]; then
+            if [ -n "$exact" ]; then exactdup=1; else exact=$p; fi
+          fi
+          if [ "$n" -gt "$bestn" ]; then best=$p bestn=$n dup=
+          elif [ "$n" -eq "$bestn" ] && [ "$n" -gt 0 ]; then dup=1
+          fi
+        done < <(printf '%s\n' ${lib.concatMapStringsSep " " lib.escapeShellArg
+          (lib.mapAttrsToList
+            (name: entries: "${name}:${lib.concatMapStringsSep " " (m: m.name) entries}")
+            profiles)})
+        if [ -n "$exact" ] && [ -z "$exactdup" ]; then echo "$exact"; exit 0; fi
+        if [ -n "$best" ] && [ -z "$dup" ]; then echo "$best"; exit 0; fi
+        exit 1 ;;
       *)
-        echo "usage: nomarchy-display-profile [list|active|apply <name>|base]" >&2
+        echo "usage: nomarchy-display-profile [list|active|apply <name>|base|match <output>...]" >&2
         exit 64 ;;
     esac
   '';
 
+  # Hotplug auto-switch (opt-in via the menu's Auto-switch row →
+  # settings.displayProfileAuto, read LIVE on every output change so the
+  # toggle is instant, no rebuild). Polls like the keyboard watcher —
+  # exec-once, not a systemd unit (graphical-session-bound units raced
+  # Hyprland's IPC on relogin; see the waybar note below). Only reacts to
+  # CHANGES after session start: the baked config already encodes the
+  # last choice, and login must not fight a deliberate manual pick.
+  # `match` picks deterministically (exact set, else unambiguous largest
+  # subset); applying via the tool persists the concrete profile, so the
+  # next rebuild bakes what auto chose.
+  displayProfileWatch = pkgs.writeShellScriptBin "nomarchy-display-profile-watch" ''
+    set -u
+    auto_on() {
+      v=$(${sync} get settings.displayProfileAuto 2>/dev/null) || v=false
+      case "$v" in true|True) return 0 ;; *) return 1 ;; esac
+    }
+    outputs() { hyprctl monitors all -j 2>/dev/null | jq -r '.[].name' | sort; }
+    prev=$(outputs)
+    while :; do
+      sleep 3
+      cur=$(outputs)
+      [ "$cur" = "$prev" ] && continue
+      prev=$cur
+      [ -n "$cur" ] || continue
+      auto_on || continue
+      target=$(nomarchy-display-profile match $cur) || continue
+      [ "$target" = "$(nomarchy-display-profile active)" ] && continue
+      nomarchy-display-profile apply "$target"
+    done
+  '';
+
   # 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
@@ -228,7 +289,8 @@ in
         # the clean pkill a theme switch now does — respawns the bar instead
         # of orphaning the session bar-less.
       ] ++ lib.optional config.nomarchy.waybar.enable "nomarchy-waybar"
-        ++ lib.optional kbAutoSwitch "${keyboardWatch}/bin/nomarchy-keyboard-watch";
+        ++ lib.optional kbAutoSwitch "${keyboardWatch}/bin/nomarchy-keyboard-watch"
+        ++ lib.optional (profiles != { }) "${displayProfileWatch}/bin/nomarchy-display-profile-watch";
 
       # ── Theme-driven look ──────────────────────────────────────────
       # These flow from theme-state.json and stay at NORMAL priority:
@@ -375,6 +437,8 @@ in
     # 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
-    # The display-profile switcher (the menu's Profiles row gates on it).
-    ++ lib.optional (config.nomarchy.hyprland.enable && profiles != { }) displayProfileTool;
+    # The display-profile switcher (the menu's Profiles row gates on it)
+    # + its hotplug watcher, on PATH for debugging like the keyboard one.
+    ++ lib.optionals (config.nomarchy.hyprland.enable && profiles != { })
+         [ displayProfileTool displayProfileWatch ];
 }

modules/home/rofi.nix

@@ -394,11 +394,26 @@ ${themeRows}
             if [ "$p" = "$active" ]; then printf '● %s\n' "$p"; else printf '○ %s\n' "$p"; fi
           done
           printf 'Base layout\n'
+          if [ "$(nomarchy-theme-sync get settings.displayProfileAuto 2>/dev/null)" = true ]
+          then printf 'Auto-switch (on)\n'
+          else printf 'Auto-switch (off)\n'
+          fi
           printf '%s\n' "$BACK"
         } | rofi -dmenu -p Profiles ) || exit 0
         case "$choice" in
           "$BACK")        exec "$0" display ;;
           "Base layout")  exec nomarchy-display-profile base ;;
+          *"Auto-switch"*)
+            # Instant in-flake flag; the watcher reads it live on the next
+            # output change — no rebuild, no unit juggling.
+            if [ "$(nomarchy-theme-sync get settings.displayProfileAuto 2>/dev/null)" = true ]; then
+              nomarchy-theme-sync --quiet set settings.displayProfileAuto false --no-switch
+              notify-send "Display profiles" "Auto-switch off — profiles change only from this menu."
+            else
+              nomarchy-theme-sync --quiet set settings.displayProfileAuto true --no-switch
+              notify-send "Display profiles" "Auto-switch on — plugging/unplugging outputs picks the matching profile."
+            fi
+            exec "$0" display-profile ;;
           *)              exec nomarchy-display-profile apply "''${choice#[●○] }" ;;
         esac ;;