fix(iso): recover memtest after live-build

bible-local/decisions/2026-04-01-memtest-build-strategy.md

@@ -23,6 +23,63 @@ Current evidence from the archived `easy-bee-nvidia-v3.14-amd64` logs dated 2026
 
 So the assumption "live-build built-in memtest integration is enough on this stack" is currently false for this project until proven otherwise by a real built ISO.
 
+Additional evidence from the archived `easy-bee-nvidia-v3.17-dirty-amd64` logs dated 2026-04-01:
+
+- the build now completes successfully because memtest is non-blocking by default
+- `lb binary_memtest` still runs and installs `memtest86+`
+- the project-owned hook `config/hooks/normal/9100-memtest.hook.binary` does execute
+- but it executes too early for its current target paths:
+  - `binary/boot/grub/grub.cfg` is still missing at hook time
+  - `binary/isolinux/live.cfg` is still missing at hook time
+  - memtest binaries are also still absent in `binary/boot/`
+- later in the build, live-build does create intermediate bootloader configs with memtest lines in the workdir
+- but the final ISO still lacks memtest binaries and still lacks memtest lines in extracted ISO `boot/grub/grub.cfg` and `isolinux/live.cfg`
+
+So the assumption "the current normal binary hook path is late enough to patch final memtest artifacts" is also false.
+
+## Known Failed Attempts
+
+These approaches were already tried and should not be repeated blindly:
+
+1. Built-in live-build memtest only.
+Reason it failed:
+- `lb binary_memtest` runs, but the final ISO still misses memtest binaries and menu entries.
+
+2. Fixing only the memtest file names for Debian Bookworm.
+Reason it failed:
+- correct file names alone do not make the files appear in the final ISO.
+
+3. Copying memtest from `chroot/boot/` into `binary/boot/` via a binary hook.
+Reason it failed:
+- in this stack `chroot/boot/` is often empty for memtest payloads at the relevant time.
+
+4. Fallback extraction from cached `memtest86+` `.deb`.
+Reason it failed:
+- this was explored already and was not enough to stabilize the final ISO path end-to-end.
+
+5. Restoring explicit memtest menu entries in source bootloader templates only.
+Reason it failed:
+- memtest lines in source templates or intermediate workdir configs do not guarantee the final ISO contains them.
+
+6. Patching `binary/boot/grub/grub.cfg` and `binary/isolinux/live.cfg` from the current `config/hooks/normal/9100-memtest.hook.binary`.
+Reason it failed:
+- the hook runs before those files exist, so the hook cannot patch them there.
+
+## What This Means
+
+When revisiting memtest later, start from the constraints above rather than retrying the same patterns:
+
+- do not assume the built-in memtest stage is sufficient
+- do not assume `chroot/boot/` will contain memtest payloads
+- do not assume source bootloader templates are the last writer of final ISO configs
+- do not assume the current normal binary hook timing is late enough for final patching
+
+Any future memtest fix must explicitly identify:
+
+- where the memtest binaries are reliably available at build time
+- which exact build stage writes the final bootloader configs that land in the ISO
+- and a post-build proof from a real ISO, not only from intermediate workdir files
+
 ## Decision
 
 For `bee`, memtest must be treated as an explicit ISO artifact with explicit post-build validation.
@@ -44,12 +101,17 @@ Project rules from now on:
 Current implementation direction:
 
 - keep the live-build memtest stage enabled if it helps package acquisition
-- but enforce memtest explicitly in a project-owned binary hook
-- patch the generated `binary/boot/grub/grub.cfg` and `binary/isolinux/live.cfg` directly in the binary stage if memtest entries are missing
+- do not rely on the current early `binary_hooks` timing for final patching
+- prefer a post-`lb build` recovery step in `build.sh` that:
+  - patches the fully materialized `LB_DIR/binary` tree
+  - injects memtest binaries there
+  - ensures final bootloader entries there
+  - reruns late binary stages (`binary_checksums`, `binary_iso`, `binary_zsync`) after the patch
 
 ## Consequences
 
 - Future memtest changes must begin by reading this ADR and the commits listed above.
+- Future memtest changes must also begin by reading the failed-attempt list above.
 - We should stop re-introducing "prefer built-in live-build memtest" as a default assumption without new evidence.
 - Memtest validation in `build.sh` is not optional; it is the acceptance gate that prevents another silent regression.
 - If we change memtest strategy again, we must update this ADR with the exact build evidence that justified the change.