diff --git a/.vscode/settings.json b/.vscode/settings.json
index ee9ab88..d598a4e 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -14,14 +14,13 @@
 		"--header-insertion=never"
 	],
 
-	// The presets are the build interface; the toolchain file inside the
-	// libavr submodule is the one place the compiler is chosen. The submodule
-	// carries no local/toolchain for it to discover, so the prefix is named
-	// here, for the window that opens this folder.
+	// The presets are the build interface, and the toolchain file inside the
+	// libavr submodule is the one place the compiler is chosen. **No prefix is
+	// named here**: a committed file may not name a path that is true of one
+	// machine (libavr guidance rule 50), so the gitignored local/machine.cmake
+	// at this repository's root is where a checkout says where its toolchain
+	// is - one file, and it answers for both hosts.
 	"cmake.useCMakePresets": "always",
-	"cmake.environment": {
-		"LIBAVR_TOOLCHAIN": "D:/dev/libavr/local/toolchain/avr-gcc-16.1.0-mingw"
-	},
 	"cmake.configureOnOpen": true,
 	"cmake.options.statusBarVisibility": "compact",
 
diff --git a/libavr b/libavr
index 8521f48..00d669b 160000
--- a/libavr
+++ b/libavr
@@ -1 +1 @@
-Subproject commit 8521f48a3361100c5f3e3c5004a5ff415e2d1484
+Subproject commit 00d669b4510579d202bac059f46246448d5cac3b
diff --git a/tools/check.sh b/tools/check.sh
new file mode 100755
index 0000000..40de33e
--- /dev/null
+++ b/tools/check.sh
@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+# The task gate: every configure preset built, and only then every one tested.
+#
+# The loop itself is libavr's (tools/check-presets.sh) because the order in it
+# is subtle and was got wrong by hand more than once - the mode-identity checks
+# read the sibling mode's tree, so a build-then-test-per-preset run compares a
+# fresh image against a stale sibling. Anything this repository needs beyond
+# the presets is written after the call, where every tree is built and tested.
+set -euo pipefail
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+"${LIBAVR_ROOT:-libavr}/tools/check-presets.sh" "$@"