feat(idle): suspend on battery only, cohering with power management

hypridle's suspend listener now runs `nomarchy-on-ac || systemctl
suspend`, so a plugged-in machine no longer suspends itself mid-idle
(long builds, media, presentations survive). It also fires sooner —
15 min, vs the old fixed 30 — since it now only applies unplugged.
Lock and screen-off are unchanged on both power sources, and logind's
lid handling stays at its sensible defaults (suspend on lid close,
ignore when docked).

Closes the idle-cohesion follow-up under the laptop-power roadmap item.

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

README.md

@@ -454,10 +454,15 @@ close · `SUPER+1..9` workspaces · `Print` region screenshot.
     default; the installer scaffolds it commented-out on laptops.
   - ✓ **installer:** writes `power.laptop = true` (battery probe) and
     `power.thermal.enable` (Intel) into the generated `system.nix`.
-  - Remaining: **cohere** with `modules/home/idle.nix` (AC-vs-battery idle
-    timeouts / no auto-suspend on AC) and review logind lid handling, plus a
-    boot-only→event-driven charge-limit re-apply (udev) if a firmware resets
-    the threshold on unplug.
+  - ✓ **idle cohesion:** `modules/home/idle.nix` now suspends only on
+    battery (and sooner — 15 min vs the old fixed 30), gating the hypridle
+    suspend listener on a `nomarchy-on-ac` probe so a plugged-in machine
+    stays up mid-idle; lock/screen-off are unchanged on both sources.
+    logind's lid handling is left at its defaults (suspend on lid close,
+    ignore when docked) — an explicit "I'm done" that coheres with the
+    idle behaviour.
+  - Remaining: a boot-only→event-driven charge-limit re-apply (udev) if a
+    firmware resets the threshold on unplug.
 - **Opt-in services & integrations:** the counterpart to the opt-*out*
   application suite above — heavier or more personal integrations shipped
   **off by default**, each a `nomarchy.services.<name>.enable` toggle a

modules/home/idle.nix

@@ -2,13 +2,23 @@
 # theme-state.json. One concern, one file: hypridle drives WHEN (idle
 # lock, display off, suspend, lock-before-sleep), hyprlock is the
 # themed lock screen itself (also behind the power menu's Lock entry).
-{ config, lib, ... }:
+{ config, lib, pkgs, ... }:
 
 let
   cfg = config.nomarchy;
   t = cfg.theme;
   c = t.colors;
   inherit (config.nomarchy.lib) rgb;
+
+  # Exits 0 when running on AC: a mains adapter reports `online` 1 (battery
+  # supplies have no `online` node, so they never match). Used as
+  # `${onAc} || <action>` so the action is skipped while plugged in.
+  onAc = pkgs.writeShellScript "nomarchy-on-ac" ''
+    for f in /sys/class/power_supply/*/online; do
+      [ -r "$f" ] && [ "$(cat "$f")" = "1" ] && exit 0
+    done
+    exit 1
+  '';
 in
 {
   config = lib.mkIf cfg.idle.enable {
@@ -62,13 +72,20 @@ in
           after_sleep_cmd = "hyprctl dispatch dpms on";
         };
         listener = [
+          # Lock and screen-off are the same on either power source —
+          # they're about privacy and the panel, not battery.
           { timeout = 300; on-timeout = "loginctl lock-session"; }
           {
             timeout = 600;
             on-timeout = "hyprctl dispatch dpms off";
             on-resume = "hyprctl dispatch dpms on";
           }
-          { timeout = 1800; on-timeout = "systemctl suspend"; }
+          # Suspend only on battery, and sooner than the old fixed 30 min
+          # (it now only fires unplugged). Plugged in, the machine stays
+          # up — long builds, media, presentations aren't killed mid-idle.
+          # Closing the lid still suspends on AC (logind's default): that's
+          # an explicit "I'm done", distinct from sitting idle.
+          { timeout = 900; on-timeout = "${onAc} || systemctl suspend"; }
         ];
       };
     };