Small fix, rewrite the Package builds section

This MR:

• removes the use of snapshotted
• rewrites the Package builds section adding more details about package builds using the SDK, devroots and snapshots of APT archives. It mentions the differences between building on OBS and on the SDK and differences between native and emulated builds.

content/architecture/long-term-reproducibility.md

@@ -308,14 +308,55 @@ the remaining planned improvements.
 
 ## Package builds
 
-Package builds happen on OBS which does not have snapshotting capabilities and
-always builds every package on a clean, isolated environment built using the
-latest package versions for each channel.
-
-Since the purposes taken in account in this document do not involve large scale
-package rebuilds, it is recommended to use the SDK images and the devroots in
-combination with APT archives snapshots to rebuild packages in an
-environment closely matching a past build.
+Apertis uses [OBS](https://openbuildservice.org/) for building packages,
+however since the purpose of the long term reproducibility does not involve
+large scale package rebuilds, we recommend using the [Apertis
+SDK]({{< ref "software-development-kit.md" >}}) for building packages. In addition to
+the SDK a [devroot]({{< ref "sysroots-and-devroots/#devroot" >}}) and a snapshot
+of the APT repositories are also required.
+
+We recommend the SDK release to match the release of Apertis in the target
+device, and it is important that both the release and architecture of the
+devroot and of the snapshot of the APT repositories matches the target device.
+As an example, if the target is an `ARM64` device, the devroot and the snapshot
+of the APT repositories should also be for `ARM64`.
+
+See the [devroot]({{< ref "sysroots-and-devroots/#devroot" >}}) for more
+information.
+
+For the long term reproducibility we recommend the product team to have a
+backup copy of:
+ * The Apertis SDK: Matching the Apertis release in use by the target device.
+ * The Apertis devroot: Matching the Apertis release and the architecture of
+   the target device.
+
+At the time of writing OBS supports native and emulated builds, and we have
+successfully deployed emulated builds on the Bosch Developer Cloud. While
+emulated builds are expected to work in most cases, they may require
+changes to the packages being build using emulation, and they may produce
+different results when compared to native builds.
+
+For more information about emulated and native builds see
+[Build infrastructure on Intel x86-64]({{< ref "x86-build-infrastructure.md" >}}).
+
+Building packages on the SDK uses emulation, and while this approach is
+currently expected to be satisfactory, it may produce different results when
+compared to native builds. In the unlikely event of emulated builds not being
+satisfactory, we describe a mitigation on the section Future work on package
+builds.
+
+### Future work on package builds
+
+We recommend using the Apertis SDK for building packages in the context of the
+long term reproducibility to enable product teams to build packages without
+depending on custom OBS deployments.
+
+However using OBS for building packages in the context of the long term
+reproducibility may offer advantages, when large package rebuilds are needed or
+when native builds are required.
+
+We will consider for future work automating the OBS configuration to support
+building packages for the long term reproducibility.
 
 # Recommendations for product teams