Problem with local / `file:` repository

[cmahnke]

I'm not sure if this is the right repository or if I should report to mmdebstrap. Anyways I'm using the YAML config so I'll add it here:

I've defined a mirror like this

mmdebstrap:
  mirrors:
    - deb [ trusted=yes ] file:///debian/debian ./

Having this in /etc/apt/sources.list works as expected

This works to a certain degree, up until the installation, note that the path is clearly wrong:

E: Failed to fetch file:/debian/debian/debian/cage_0.2.0-cursor_arm64.deb  File not found - /debian/debian/debian/cage_0.2.0-cursor_arm64.deb (2: No such file or directory)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
E: setup failed: E: apt-get -o Dir::Bin::dpkg=env -o DPkg::Options::=--unset=TMPDIR -o DPkg::Options::=dpkg -o DPkg::Chroot-Directory=/opt/rpi-image-gen/work/magisch-app/rootfs --yes install -oAPT::Status-Fd=<$fd> -oDpkg::Use-Pty=false ca-certificates raspberrypi-archive-keyring raspi-config rpi-eeprom raspi-utils raspi-utils-core raspi-utils-dt flashrom cryptsetup e2fsprogs wget net-tools iputils-ping procps nano zstd raspi-firmware linux-image-rpi-v8 sudo keyboard-configuration console-data console-setup kbd less busybox systemd systemd-sysv systemd-timesyncd fake-hwclock libgbm1 cage openssh-server failed
I: main() received signal PIPE: waiting for setup...
E: mmdebstrap failed to run

Trying to be smart and removing a path component gives:

E: Failed to fetch file:/debian/./Packages  File not found - /debian/./Packages (2: No such file or directory)
E: Some index files failed to download. They have been ignored, or old ones used instead.
E: apt-get update --error-on=any -oAPT::Status-Fd=<$fd> -oDpkg::Use-Pty=false failed
I: main() received signal PIPE: waiting for setup...
E: mmdebstrap failed to run

Adding a slash to the end of the path, didn't change anything either...

Also a simple ln -s /debian/debian /debian/debian/debian won't work around it, but reveals the real issue:

Chrooting into /opt/rpi-image-gen/work/magisch-app/rootfs/
dpkg: error: cannot stat pathname '/tmp/apt-dpkg-install-eAVukF/141-cage_0.2.0-cursor_arm64.deb': No such file or directory
E: Sub-process env returned an error code (2)
E: setup failed: E: apt-get -o Dir::Bin::dpkg=env -o DPkg::Options::=--unset=TMPDIR -o DPkg::Options::=dpkg -o DPkg::Chroot-Directory=/opt/rpi-image-gen/work/magisch-app/rootfs --yes install -oAPT::Status-Fd=<$fd> -oDpkg::Use-Pty=false ca-certificates raspberrypi-archive-keyring raspi-config rpi-eeprom raspi-utils raspi-utils-core raspi-utils-dt flashrom cryptsetup e2fsprogs wget net-tools iputils-ping procps nano zstd raspi-firmware linux-image-rpi-v8 sudo keyboard-configuration console-data console-setup kbd less busybox systemd systemd-sysv systemd-timesyncd fake-hwclock libgbm1 cage openssh-server failed
I: main() received signal PIPE: waiting for setup...
E: mmdebstrap failed to run