Seafile discontinued linux-clients.seafile.com: it resolves but accepts
no connections on 80 or 443, and the official docs no longer mention APT
at all. Every `docker build` has failed since. Upstream now ships the CLI
as an AppImage, so install 9.0.19 from the download site.
The AppImage is unpacked rather than executed. Running one needs FUSE and
so a privileged container, and its self-extraction also fails when the
build host cannot execute the payload's architecture. Unpacking the
appended squashfs directly avoids both.
Also add the bundled seafile/pysearpc bindings to the venv path. The APT
package installed them system-wide, where `venv --system-site-packages`
picked them up; dsc imports seafile directly for RPC, not only through
seaf-cli, so it broke when that implicit dependency went away.
Drops apt-key, pins the version, and verifies a SHA256 before unpacking.
Build-time smoke checks assert the seaf-cli subcommands and the app's own
imports.
Note: the AppImage is x86_64-only, and upstream publishes no digest or
signature, so the pinned checksum is trust-on-first-use.
Maxim Shulga
snegov
Ludovic Frank
Robin Grönberg