feat(display): blackout rescue — re-enable a disabled panel on undock

Bernardo's question: with "Laptop screen off" active, does the panel
come back when the dock is yanked? VM answer (new maintainer harness
tools/monitor-fallback.nix, softGL desktop): no — Hyprland 0.55.4
leaves the session with zero active outputs and never re-enables a
soft-disabled monitor. rescue_blackout in the display hotplug watcher
now re-enables every disabled output (immediate, retried, idempotent
keyword + toast) whenever a monitorremoved leaves nothing active;
independent of the profile auto-switch and its settings gate.

Sharp edge documented rather than hidden: the zero-output state itself
crashes Hyprland in the VM ~4/5 runs (aquamarine CBackend::dispatchIdle
ABRT within ~0.5s — faster than any userland rescue; a control run
removing the external with the panel ACTIVE survives 5/5, so the state
is the trigger, not headless removal; crash reproduced with the rescue
provably inert, so not caused by it). Rescue ships as defense-in-depth:
it recovers every surviving case, and the worst case on real DRM is
session-to-greeter on a re-lit panel instead of a black brick. Rider
fix: `grep -c .` exits 1 at count zero — the ||-guard on that pipeline
silently disabled the rescue exactly when it mattered.

Verified: hazard V2 (VM reproduces the dead state); control
discriminator 5/5; flake check green. V3 pending: real-dock
undock-while-off in HARDWARE-QUEUE (run with nothing important open;
crash on real DRM = rework the row to mirror or wait for a Hyprland
bump).

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

agent/HARDWARE-QUEUE.md

@@ -48,6 +48,17 @@ the **T14s** (webcam case).
       shows "Send output → <dock sink>" when one exists and isn't
       default; picking it moves output + toasts. Pass = rows appear/act
       as described, and none of them show on a single-display session.
+      Also — **run this one with nothing important open**: with the
+      laptop screen off via the menu, physically unplug the dock. The
+      panel should re-enable within ~2s (`rescue_blackout` in the
+      display watcher). Known risk from the VM harness
+      (tools/monitor-fallback.nix): on Hyprland 0.55.4 the zero-output
+      state itself can crash the compositor faster than any rescue
+      (softGL VM: 4/5 runs; control with the panel active survives
+      always) — a crash on real DRM ends the session to the greeter on
+      the re-lit panel. If that happens on hardware, the "Laptop screen
+      off" row needs a rework (mirror instead of disable, or drop until
+      a Hyprland bump) — file it as a NOW bug with the coredump.
 - [ ] **#55 fingerprint enroll on real reader** — with
       `nomarchy.hardware.fingerprint.enable` and a physical reader: System ›
       Fingerprint › Enroll a finger; List shows it; Verify succeeds; optional

agent/JOURNAL.md

@@ -19,6 +19,26 @@ Template:
 
 ---
 
+## 2026-07-12 — undock blackout rescue (interactive follow-up)
+- **Task:** Bernardo: "if I turn the laptop screen off and undock, does
+  the panel come back?" Answer had to be tested, not recalled.
+- **Did:** Built tools/monitor-fallback.nix (softGL desktop VM, crib of
+  theme-shot): headless "external" + menu's exact disable + output
+  remove. Verdict: Hyprland 0.55.4 does NOT re-enable → shipped
+  `rescue_blackout` in the display hotplug watcher (immediate + retried
+  keyword re-enable of disabled outputs on zero-active, toast).
+- **Verified:** V2 for the hazard (VM reproduced the dead state);
+  rescue itself is V1+components — the VM crashes before rescue can act
+  in 4/5 runs (aquamarine ABRT in dispatchIdle on the zero-output
+  state; control with panel active survives 5/5 — discriminator run).
+  Crash predates rescue (run with rescue provably inert also crashed).
+  Also fixed: `grep -c .` exit-1-at-zero disabling the rescue's own
+  trigger. flake check green.
+- **Pending:** real-dock V3 (HARDWARE-QUEUE, "nothing important open"
+  warning); if real DRM crashes too → rework row (mirror) or wait for
+  Hyprland bump; consider reporting upstream with the coredump.
+- **Next suggestion:** dock V3 results, then #89 slice 3.
+
 ## 2026-07-12 — dock audio auto-follow + docked menu rows (interactive)
 - **Task:** Bernardo's dock test (= #87's V3): audio stayed on speakers,
   had to hand-tweak EasyEffects; wants docked Display/Audio menu options.

docs/ROADMAP.md

@@ -424,6 +424,25 @@ Design/decision records and a running log of shipped work (items marked
   (`swapactiveworkspaces`, exactly-2 gate); Audio gains a self-gated
   "Send output → <dock sink>" quick row (the watcher's manual override).
   Real-dock V3 for both in HARDWARE-QUEUE.
+  ✓ **Undock blackout rescue (2026-07-12):** Bernardo asked whether the
+  panel comes back if you undock while "Laptop screen off" — VM answer
+  (tools/monitor-fallback.nix, full softGL desktop): **no**, Hyprland
+  0.55.4 leaves zero active outputs and never re-enables a soft-disabled
+  monitor. Fix: `rescue_blackout` in the display hotplug watcher
+  (hyprland.nix) — on monitorremoved with zero active outputs,
+  immediately (and with retries) `keyword monitor <name>,preferred,auto,
+  auto` every disabled output + toast; independent of the profile
+  auto-switch gate (safety invariant, not a preference). Sharp edge
+  found while testing: the zero-output state itself crashes Hyprland in
+  the VM ~4/5 runs (ABRT in aquamarine CBackend::dispatchIdle, ~0.5s —
+  faster than any userland rescue; control run with the panel active
+  survives 5/5, so it's the state, not headless removal; monitor-
+  disconnect crashes are a known upstream class). Posture: rescue ships
+  as defense-in-depth (recovers every surviving case; worst case on real
+  DRM is session-to-greeter on the re-lit panel, not a black brick);
+  V3 decides if the menu row needs a mirror-based rework. Also fixed in
+  the rescue: `grep -c .` exits 1 at count 0 — an `||`-guard on that
+  pipeline silently disabled the rescue exactly when it mattered.
   ✓ **neon-glass finish (#88, `VISION § D`):** rewrote whole-swap
   `rofi.rasi` to rofi-native `@color` glass panel (cyan rim, soft
   selection wash — same hex-alpha glass pattern as Boreal); btop title/

docs/TESTING.md

@@ -105,6 +105,11 @@ unattended env it uses is in the script, and the same flow works
 interactively from the live terminal. If the desktop comes up unthemed,
 read `/var/log/nomarchy-hm-preactivate.log` on the installed system.
 
+Two full-desktop VM harnesses (softGL Hyprland, too heavy for `checks.*`)
+live next to the scripts: `tools/theme-shot.nix` (themed-desktop
+screenshots) and `tools/monitor-fallback.nix` (undock blackout rescue —
+disabled panel must re-enable when the last active output disappears).
+
 ## 5. VM-specific gotchas
 
 - **No KVM** (e.g. nested without acceleration): everything works but

modules/home/hyprland.nix

@@ -215,7 +215,43 @@ ${lib.concatStringsSep "\n" (lib.mapAttrsToList
       case "$v" in true|True) return 0 ;; *) return 1 ;; esac
     }
     outputs() { hyprctl monitors all -j 2>/dev/null | jq -r '.[].name' | sort; }
-    
+
+    # Blackout rescue — the session must never end up with ZERO active
+    # outputs. Hyprland does NOT re-enable a soft-disabled monitor when
+    # the last active one disconnects (VM-verified, tools/
+    # monitor-fallback.nix): menu "Laptop screen off" + sudden undock
+    # left a dead session. On every monitorremoved, if nothing is
+    # active, re-enable whatever is disabled (preferred/auto — the
+    # declared rule returns at the next reload/relogin). Independent of
+    # the profile auto-switch and its settings gate: this is a safety
+    # invariant, not a layout preference.
+    active_count() {
+      # NB: `grep -c .` exits 1 when the count is 0 — the case this whole
+      # rescue exists for — so never `||`-guard on the pipeline status.
+      hyprctl monitors -j 2>/dev/null | jq -r '.[].name' | grep -c . || true
+    }
+    rescue_blackout() {
+      # Act IMMEDIATELY and retry: the zero-output state is not just a
+      # black screen, it can kill the compositor outright — in the softGL
+      # VM harness aquamarine ABRT'd (CBackend::dispatchIdle) within
+      # ~0.5s of the last output going while it persisted, so shrinking
+      # the window is the priority; the keyword is idempotent and the
+      # retries cover a first attempt racing the removal teardown.
+      tries=0
+      while [ "$(active_count)" = 0 ] && [ "$tries" -lt 4 ]; do
+        hyprctl monitors all -j 2>/dev/null | jq -r '.[] | select(.disabled) | .name' \
+        | while read -r m; do
+            [ -n "$m" ] || continue
+            hyprctl keyword monitor "$m,preferred,auto,auto" >/dev/null 2>&1
+          done
+        tries=$((tries+1))
+        sleep 1
+      done
+      if [ "$tries" -gt 0 ] && [ "$(active_count)" != 0 ]; then
+        notify-send "Display" "Screen re-enabled — the active output disappeared." 2>/dev/null || true
+      fi
+    }
+
     check_monitors() {
       cur=$(outputs)
       [ "$cur" = "$1" ] && return
@@ -239,7 +275,12 @@ ${lib.concatStringsSep "\n" (lib.mapAttrsToList
     # Listen to Hyprland's IPC socket for instant hotplug reaction
     ${pkgs.socat}/bin/socat -U - UNIX-CONNECT:$XDG_RUNTIME_DIR/hypr/$HYPRLAND_INSTANCE_SIGNATURE/.socket2.sock | while read -r line; do
       case "$line" in
-        monitoradded*|monitorremoved*)
+        monitorremoved*)
+          rescue_blackout
+          res=$(check_monitors "$prev")
+          [ -n "$res" ] && prev="$res"
+          ;;
+        monitoradded*)
           res=$(check_monitors "$prev")
           [ -n "$res" ] && prev="$res"
           ;;

tools/monitor-fallback.nix

@@ -0,0 +1,110 @@
+# Undock blackout-rescue harness — boots the full desktop headlessly
+# (softGL Hyprland, same recipe as theme-shot.nix) and replays the
+# dangerous sequence: add a headless "external", soft-disable the
+# internal panel (the Display menu's "Laptop screen off" command), then
+# remove the external. Hyprland does NOT re-enable a disabled monitor on
+# its own (verified 2026-07-12 — the session ends with zero active
+# outputs), so the display-profile watcher's rescue_blackout
+# (modules/home/hyprland.nix) must bring the panel back; this asserts it
+# does. KNOWN FLAKE (2026-07-12, Hyprland 0.55.4): the zero-active-output
+# state itself crashes Hyprland in this VM ~4/5 runs (ABRT in aquamarine
+# CBackend::dispatchIdle, faster than any userland rescue) — a control
+# run removing the external with the internal ACTIVE survives every
+# time, so it's the zero-output state, not headless removal. A crashed
+# run is that upstream bug, not a rescue regression; the assertion can
+# only pass on a surviving run. Maintainer tool, NOT a checks.* gate
+# (full-desktop VM — same weight call as theme-shot.nix). Run:
+#   nix build --impure -f tools/monitor-fallback.nix --no-link -L
+let
+  flake = builtins.getFlake ("git+file://" + toString ../.);
+  inherit (flake.inputs) nixpkgs home-manager;
+  pkgs = import nixpkgs {
+    system = "x86_64-linux";
+    overlays = [ flake.overlays.default ];
+    config.allowUnfree = true;
+  };
+in
+pkgs.testers.runNixOSTest {
+  name = "monitor-fallback";
+  node.pkgsReadOnly = false;
+  node.specialArgs = { username = "nomarchy"; };
+  nodes.machine = { pkgs, lib, ... }: {
+    imports = [ flake.nixosModules.nomarchy home-manager.nixosModules.home-manager ];
+    virtualisation.memorySize = 4096;
+    virtualisation.cores = 4;
+    hardware.graphics.enable = true;
+    environment.variables.LIBGL_ALWAYS_SOFTWARE = "1";
+    boot.initrd.availableKernelModules = [ "virtio_gpu" ];
+    virtualisation.qemu.options = [ "-vga none" "-device virtio-gpu-pci,xres=1920,yres=1080" ];
+    users.users.nomarchy = {
+      isNormalUser = true;
+      password = "test";
+      extraGroups = [ "wheel" "video" ];
+    };
+    nomarchy.system.stateFile = flake + "/themes/boreal.json";
+    systemd.tmpfiles.rules = [
+      "d /home/nomarchy/.nomarchy 0755 nomarchy users -"
+      "C /home/nomarchy/.nomarchy/theme-state.json 0644 nomarchy users - ${flake + "/themes/boreal.json"}"
+    ];
+    services.greetd.settings.initial_session = {
+      command = "start-hyprland";
+      user = "nomarchy";
+    };
+    home-manager.useGlobalPkgs = true;
+    home-manager.users.nomarchy = {
+      imports = [ flake.homeModules.nomarchy ];
+      nomarchy.stateFile = flake + "/themes/boreal.json";
+      nomarchy.idle.enable = false;
+    };
+  };
+  testScript = ''
+    import json, time
+
+    machine.wait_for_unit("multi-user.target")
+    machine.wait_for_file("/run/user/1000/hypr", 180)
+    machine.sleep(20)  # softGL first paint settle
+
+    hy = ("su - nomarchy -c 'XDG_RUNTIME_DIR=/run/user/1000 "
+          "HYPRLAND_INSTANCE_SIGNATURE=$(ls /run/user/1000/hypr | head -1) hyprctl ")
+
+    def mons(all=False):
+        out = machine.succeed(hy + ("-j monitors all'" if all else "-j monitors'"))
+        return json.loads(out)
+
+    initial = mons()
+    assert len(initial) == 1, f"expected 1 initial monitor, got {initial}"
+    internal = initial[0]["name"]
+    print(f"internal panel: {internal}")
+
+    # "Plug the dock": add a headless output as the external monitor.
+    machine.succeed(hy + "output create headless'")
+    for _ in range(20):
+        if len(mons()) == 2: break
+        time.sleep(1)
+    names = [x["name"] for x in mons()]
+    ext = [n for n in names if n != internal][0]
+    print(f"external (headless): {ext}")
+
+    # Menu action: "Laptop screen off" — the exact command the row runs.
+    machine.succeed(hy + f"keyword monitor {internal},disable'")
+    for _ in range(20):
+        if [x["name"] for x in mons()] == [ext]: break
+        time.sleep(1)
+    assert [x["name"] for x in mons()] == [ext], f"disable failed: {mons()}"
+    alln = {x["name"]: x.get("disabled", False) for x in mons(all=True)}
+    assert alln.get(internal) is True, f"{internal} not marked disabled: {alln}"
+    print("laptop panel disabled, only external active — now yank it")
+
+    # Sudden undock: remove the external while the internal is disabled.
+    machine.succeed(hy + f"output remove {ext}'")
+    recovered = False
+    for i in range(30):
+        if [x["name"] for x in mons()] == [internal]:
+            recovered = True
+            print(f"recovered after {i+1}s: {internal} re-enabled")
+            break
+        time.sleep(1)
+    print(f"monitors now: {mons(all=True)}")
+    assert recovered, "internal panel did NOT come back after undock"
+  '';
+}