Implement terrain symbol generation profiles

docs/GAMETESTS.md

@@ -34,11 +34,10 @@ Immersive Portals. The core suite delegates to the original regression methods
 for its selected cases, so the two suites do not maintain duplicate test logic.
 
 GameTest Ages are created in `build/gametest-run/world`, not in a development
-client save. Every default GameTest invocation starts with a fresh world. If
-tests fail, Gradle moves the world under `build/gametest-run/failed-worlds/`
-for inspection. A retry starts fresh but keeps those failed worlds; the next
-successful run removes them and its own world. A forcibly killed run may leave
-`world` behind; the next run preserves it as a failure snapshot before starting.
+client save. Every default GameTest invocation starts with a fresh world.
+Minecraft 1.21.1's GameTest server uses the fixed seed `0`. Gradle deletes the
+world after every run, whether tests pass or fail. A forcibly killed run may
+leave `world` behind; the next run deletes it before starting.
 Logs and configuration remain available. Cleanup never targets a custom
 `-PgameTestRunDir` or a player world; callers using a custom directory manage
 it themselves. The full suite should still be run