Persist authored Age generation plans (#31)

docs/GAMETESTS.md

@@ -34,9 +34,12 @@ 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. The Gradle task removes that **dedicated** world automatically if
-it exceeds 512 MiB; override the threshold with `-PgameTestMaxWorldMiB=128`,
-for example. Cleanup never targets a custom `-PgameTestRunDir` or a player
-world. A fresh test world can also help diagnose a slow or stalled worldgen
-run. The full suite should still be run before shipping changes in the
-archived systems.
+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.
+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
+before shipping changes in the archived systems.