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.