Add Legacy-style Book Binder

BUILDING.txt

@@ -73,6 +73,18 @@ Or, with mise:
 
 All required GameTests should pass before distributing a build.
 
+GameTests use `build/gametest-run/world`, separate from the normal development
+world. Before each run, Gradle removes that test world if it exceeds 512 MiB.
+Override the limit with `-PgameTestMaxWorldMiB=NUMBER`. A caller-supplied
+`-PgameTestRunDir` is never removed automatically.
+
+To run the suite in a fresh temporary directory instead, use:
+
+    test_dir=$(mktemp -d /tmp/rivencraft-gametest.XXXXXX)
+    ./gradlew runGameTestServer --offline -PgameTestRunDir="$test_dir"
+
+With mise, prefix the second command with `mise exec --`.
+
 6. Locate and inspect the JAR
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