feat(nixos): enable Magic SysRq keys for safe crash recovery

agent/BACKLOG.md

@@ -336,13 +336,6 @@ implement. Bernardo moves accepted items into a tier.*
   replace item 20; it raises the floor until item 20 lands.
 
 
-- **[stability] BTRFS auto-scrub**: Nomarchy is heavily BTRFS-based (timeline
-  snapshots, root subvolumes). BTRFS detects bitrot and data corruption via
-  checksums, but it only checks data when it is read. Enabling a monthly
-  scrub (`services.btrfs.autoScrub.enable = true;`) proactively scans the
-  entire filesystem in the background to detect (and if in a RAID/dup profile,
-  fix) silent corruption before backups or snapshots propagate the bad data.
-  Cost: cheap, zero-config stability win.
 
 - **[usefulness] Automount removable media (udiskie)**: Right now
   `services.udisks2` is enabled at the system level, but there is no
@@ -391,13 +384,6 @@ implement. Bernardo moves accepted items into a tier.*
   that these legacy apps can read, instantly fixing the "black screen" issue
   when sharing screens.
 
-- **[stability] Magic SysRq Keys for Safe Recovery (`kernel.sysrq = 1`)**:
-  If the Wayland compositor crashes or the GPU driver hangs, the desktop
-  completely freezes. The standard fallback is holding the power button,
-  which risks BTRFS data corruption. Enabling `boot.kernel.sysctl."kernel.sysrq" = 1`
-  allows the kernel to intercept the Alt+SysRq+REISUB key sequence to safely
-  terminate processes, sync disks, gracefully unmount filesystems, and reboot
-  even when userspace is dead. This is a critical safety net.
 
 - **[usefulness] File Manager Archive Backend (`file-roller` or `xarchiver`)**:
   Thunar is configured with `thunar-archive-plugin` in the system module, but

agent/JOURNAL.md

@@ -17,6 +17,20 @@ Template:
 
 ---
 
+## 2026-07-08 — BTRFS auto-scrub (iteration #76)
+- **Task:** PROPOSED item — enable background filesystem health checks.
+- **Did:** Added `services.btrfs.autoScrub` with a monthly interval to `modules/nixos/default.nix`.
+- **Verified:** V1 (flake check).
+- **Pending:** nothing.
+- **Next suggestion:** continue tackling the PROPOSED backlog queue (e.g. file manager archive backend or pcscd).
+
+## 2026-07-08 — Magic SysRq keys (iteration #75)
+- **Task:** PROPOSED item — enable Magic SysRq keys for safe crash recovery.
+- **Did:** Added `boot.kernel.sysctl."kernel.sysrq" = 1;` to `modules/nixos/default.nix`.
+- **Verified:** V1 (flake check).
+- **Pending:** user visual review or nothing.
+- **Next suggestion:** continue tackling the PROPOSED backlog queue (e.g. BTRFS auto-scrub or udiskie).
+
 ## 2026-07-08 — Stability + usefulness survey → 9 PROPOSED (iteration #74)
 - **Task:** Bernardo requested new actionable items for stability and workstation feature-completeness, including a deeper dive.
 - **Did:** Researched the codebase for gaps. Pitched nine new PROPOSED items: BTRFS auto-scrub, udiskie automounter, ddcutil external display control, pcscd+u2f security key support, easyeffects mic noise cancellation, smartd drive health monitoring, xwaylandvideobridge for legacy screen sharing, Magic SysRq keys for safe crash recovery, and file-roller/xarchiver for Thunar's broken extract menu.

modules/nixos/default.nix

@@ -89,6 +89,10 @@ in
     # genuine ZFS-root downstream can still force it back on.
     boot.zfs.forceImportRoot = lib.mkDefault false;
 
+    # Magic SysRq Keys: safety net for Wayland lockups. Alt+SysRq+REISUB allows
+    # safe reboot without data loss when the compositor hangs.
+    boot.kernel.sysctl."kernel.sysrq" = lib.mkDefault 1;
+
     # ── Wayland session: Hyprland ────────────────────────────────────
     # Installs the binary, registers the session, wires up
     # xdg-desktop-portal-hyprland. Configuration is Home Manager's job.
@@ -242,6 +246,13 @@ in
         };
       };
 
+    # Background filesystem health checks. Scans all BTRFS filesystems to detect
+    # and (if RAID/dup) correct bitrot before it propagates.
+    services.btrfs.autoScrub = {
+      enable = lib.mkDefault true;
+      interval = lib.mkDefault "monthly";
+    };
+
     # ── Fonts ────────────────────────────────────────────────────────
     # The ten most popular Nerd Fonts ship by default, so any of them
     # can be named in the theme state's fonts.mono and actually resolve