C0: cap systemd-coredump on ringtail to stop game-crash lockups

Wine/Proton game segfaults (e.g. Diablo IV) produced multi-GB cores that
systemd-coredump spent minutes compressing to disk, pinning the CPU and
freezing the desktop. Cap ProcessSizeMax/ExternalSizeMax at 1G (oversized
cores logged but skipped) and MaxUse at 2G to bound the store.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/changelog.d/+ringtail-coredump-size-cap.infra.md

@@ -0,0 +1 @@
+Cap systemd-coredump on ringtail (ProcessSizeMax/ExternalSizeMax 1G, MaxUse 2G) so multi-GB Wine/Proton game crash dumps no longer thrash the disk and lock up the desktop.

nixos/ringtail/configuration.nix

@@ -609,6 +609,22 @@ in
     AllowSuspendThenHibernate=no
   '';
 
+  # Cap systemd-coredump. Wine/Proton games (Diablo IV, etc.) segfault
+  # regularly and dump multi-GB cores; with the stock (effectively unbounded)
+  # limits, systemd-coredump then spends minutes streaming and compressing the
+  # dump to disk — e.g. a single D4 crash produced a 4.6G core, read 13.7G and
+  # wrote 17.4G, pinning the CPU and locking up the desktop for ~3.5 minutes.
+  # Those cores are useless anyway: Nix .so files carry no build-id, so no
+  # backtrace can be generated. Capping uncompressed size at 1G makes oversized
+  # cores get logged-but-skipped (the kernel stops dumping once we stop reading)
+  # while real service cores (well under 1G) are still captured. MaxUse bounds
+  # the on-disk store so frequent game crashes can't accumulate (was at 8.6G).
+  systemd.coredump.extraConfig = ''
+    ProcessSizeMax=1G
+    ExternalSizeMax=1G
+    MaxUse=2G
+  '';
+
   # NixOS release
   system.stateVersion = "25.11";
 }