fix(iso): recover memtest after live-build

bible-local/docs/iso-build-rules.md

@@ -39,3 +39,17 @@ Rules:
   a real ISO.
 - If you reference memtest files manually, verify the exact package file list
   first for the target Debian release.
+
+Known bad loops for this repository:
+
+- Do not retry built-in-only memtest without new evidence. We already proved
+  that `lb binary_memtest` can run while the final ISO still has no memtest.
+- Do not assume fixing memtest file names is enough. Correct names did not fix
+  the final artifact path.
+- Do not assume `chroot/boot/` contains memtest payloads at the time hooks run.
+- Do not assume source `grub.cfg` / `live.cfg.in` are the final writers of ISO
+  bootloader configs.
+- Do not assume the current `config/hooks/normal/9100-memtest.hook.binary`
+  timing is late enough to patch final `binary/boot/grub/grub.cfg` or
+  `binary/isolinux/live.cfg`; logs from 2026-04-01 showed those files were not
+  present yet when the hook executed.