docs: file the Hyprland layoutmsg crash with preserved evidence

SIGSEGV via uncaught bad_variant_access in Layout::CAlgorithm::layoutMsg on a layoutmsg mfact dispatch. Upstream bug, seen on v0.54.1 (March) and v0.55.4 (today), both times from the layout-resize binds. Crash reports and tmpfs log excerpts land in working/hyprland-layoutmsg-crash/ so the evidence survives a reboot; graded [#B] (Critical x rare) in todo.org.

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diff --git a/todo.org b/todo.org
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@@ -67,6 +67,11 @@ Post-mortem for the 2026-07-15 velox no-kernel boot failure, from the archsetup/
 - Sanoid-vs-actual dataset drift: configure_zfs_snapshots configures zroot/var/log + zroot/var/lib/pacman as separate datasets; velox's actual layout has neither separate (/var/log sits inside zroot/var). Reconcile.
 - Confirm the pre-pacman snapshot hook is actually installed + firing on velox (it should be — it's what makes recovery possible).
 
+** TODO [#B] Hyprland layoutmsg crash — bad_variant_access (upstream) :bug:hyprland:
+Grading: Critical severity (SIGSEGV kills the whole desktop session; every GUI app's unsaved state lost) x rare edge case (twice in ~4.5 months: 2026-03-07 on v0.54.1, 2026-07-20 on v0.55.4) = P2 = [#B]. Upstream Hyprland bug, not this repo's code — the task tracks reporting it and picking up the fix.
+A layoutmsg mfact dispatch (layout-resize, mod+H/L) throws std::bad_variant_access inside Layout::CAlgorithm::layoutMsg, uncaught, SIGSEGV. Both crashes fired from the layout-resize mfact path (keycode 104 shrink today, 108 grow in March). Layout at crash was master and the identical mfact had worked seconds earlier; the pre-crash window held monocle<->master toggles, two window closes dropping focus to "[Window nullptr]", and togglefloating x2. Monocle is a registered v0.55 layout (log shows graceful "Unknown monocle layoutmsg" rejects), so the config is not at fault; related edges are guarded ("mfact -> no window") while this path misses its variant guard. Repo has no newer build (0.55.4-1 installed and repo).
+Evidence preserved in [[file:working/hyprland-layoutmsg-crash/][working/hyprland-layoutmsg-crash/]] (both crash reports + excerpts from the tmpfs session log, extracted before reboot loses it).
+Next: post the drafted upstream issue once approved; watch the repo for a fixed release and close on confirmation. The layout-resize script guard was declined (a script can't observe the internal desync; report-only per 2026-07-20 decision).
 ** TODO [#B] Assess a Hyprland left-drag window gesture :feature:hyprland:
 Evaluate whether a global left-click drag can move ordinary windows without
 breaking application selection, text interaction, or Wayland security