SDFs for the same package differ across Ubuntu release branches. Forward-porting is adaptation, not copy-paste. Always run deb-list.py against each target release and verify actual .deb contents.

Cross-Release Differences

Category	Example	What changes
usrmerge	`/bin/bash` -> `/usr/bin/bash`	Ubuntu 24.04+ moved binaries from `/bin/` to `/usr/bin/`. Update `contents` paths per release
t64 transition	`libssl3` -> `libssl3t64`	Ubuntu 24.04+ renamed libraries for 64-bit `time_t`. Update `essential` deps and copyright refs
Package splits/renames	Transitional packages, new soname packages	May need entirely different SDF structure or filename
Soname bumps	`librocksdb8.9` (24.04) -> `librocksdb9.10` (25.10) -> `librocksdb9.11` (26.04)	Old SDF deleted (archive no longer carries it); new SDF with new filename
Essential syntax	List (`- foo_bar`) vs map (`foo_bar:`)	Gated by the branch's `chisel.yaml` `format:`. v3 branches must use map syntax in `essential:` (the list form is a parse error, and `v3-essential:` is rejected -- fold its entries into `essential:`); v1/v2 use the list, with `v3-essential:` alongside it for arch gating
Slice granularity	`bashbug` inline in `bins` (24.04) vs separate `bashbug` slice (26.04)	Newer releases may demand finer-grained decomposition
New/removed files	New config files, removed scripts	`.deb` contents change between releases. Some paths exist in one release but not another
Dependency changes	New deps added, old deps dropped	`Depends:` may differ. Always re-check with `deb-list.py` or `apt-cache depends`

Multiarch Quirks

binutils-common per-arch despite Architecture: all-looking contents. Don't assume one SDF covers all arches without checking.
Cross-toolchain packages (<tool>-<triple>-linux-gnu, e.g. binutils-aarch64-linux-gnu) ship prefixed binaries (aarch64-linux-gnu-ld). Unprefixed symlinks (/usr/bin/ld -> aarch64-linux-gnu-ld) are not in the cross deb -- consumers create them. Convention: arch-specific SDFs leave them out; top-level binutils SDF carries the unprefixed name with a # Symlink to ${ARCH_TRIPLET}-ld comment.
/proc/self/exe workaround for chroot Java tests (chroot breaks /proc/self/exe, which the JVM launcher reads): inside the rootfs, mkdir -p "${rootfs}/proc/self" && ln -sf <path-to-java-binary> "${rootfs}/proc/self/exe" -- see the openjdk task.yaml files for the convention.