Some comments regarding forks:

the tarball must match exactly what is in pureos

How to find out what's in PureOS? Is "exactly" down to hash?

make sure you mirror that branch from Debian

Does this refer to the pristine-tar branch from the Debian package git? What if there's no git repository to mirror in Debian? Example for which I couldn't find a repo: https://packages.debian.org/source/sid/meson

do the upload manually

What does it mean?

You can find and download the tarball from any package in PureOS. All you have to do is make sure you have a line like; deb-src https://repo.puri.sm/pureos amber main in your /etc/apt/sources.list and then you can do sudo apt source . That will provide you with a pristine-tar tarball from upstream that ends with .orig.tar.gz.

Example $ sudo apt source libhandy

NOTICE: 'libhandy' packaging is maintained in the 'Git' version control system at:
https://salsa.debian.org/DebianOnMobile-team/libhandy.git
Please use:
git clone https://salsa.debian.org/DebianOnMobile-team/libhandy.git
to retrieve the latest (possibly unreleased) updates to the package.
Need to get 390 kB of source archives.
Get:1 https://repo.puri.sm/pureos amber/main libhandy 0.0.11-1pureos1 (dsc) [2,247 B]
Get:2 https://repo.puri.sm/pureos amber/main libhandy 0.0.11-1pureos1 (tar) [382 kB]
Get:3 https://repo.puri.sm/pureos amber/main libhandy 0.0.11-1pureos1 (diff) [5,736 B]
Fetched 390 kB in 1s (357 kB/s)      
dpkg-source: info: extracting libhandy in libhandy-0.0.11
dpkg-source: info: unpacking libhandy_0.0.11.orig.tar.gz
dpkg-source: info: unpacking libhandy_0.0.11-1pureos1.debian.tar.xz

It looks like Meson comes from upstream at GitHub: https://github.com/mesonbuild/meson You can pull a tarball from there if you like, though I recommend using the apt source meson method

I believe that when Guido talks about a 'manual' upload, he's referring to the use of dput; https://tracker.pureos.net/w/development/uploading_packages/

Q Can you mention some non trivial examples where we're upstream and have separate packing based on Debian? A:

• phosh: upstream packaging
• calls: upstream packaging

Maybe also include (are snippets editable??) links to the Debian packaging (i.e. salsa teams: DebianOnMobile, GNOME)

A link became outdated:

https://software.pureos.net/search_pkg

is now: https://software.pureos.net/suites