The deploy failed with "grub-install: command not found" in the chroot —
the installed rootfs archive was built BEFORE the BOOT/grub injection, so
it had no bootloader at all. build-iso.sh / build-image.sh only rebuilt
the rootfs when the archive was missing, never when sources changed, so
development fixes were silently absent from deployed images.
- build-rootfs.sh: incremental staleness check — skips a rebuild only when
no input (scripts/, btrfs/, overlays/, editions/<e>/, versions.mk,
toolchain debs) is newer than the artifact; FORCE=1 rebuilds anyway.
- build-iso.sh / build-image.sh: always delegate freshness to
build-rootfs.sh instead of gating on file existence.
- deploy-disk.sh: defensive check that grub-install exists in the deployed
rootfs, with a clear "stale archive — rebuild" message instead of a bare
"command not found".
- docs/building.md: incremental-build note (FORCE=1 / make clean).
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