It should generally be possible to restart an interrupted build, just by re-running make ...:
make: Entering directory '/root/ci_scratch/depends'
Fetching qtbase-everywhere-src-6.7.3.tar.xz from https://download.qt.io/archive/qt/6.7/6.7.3/submodules
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 280 100 280 0 0 1601 0 0
100 47.13M 100 47.13M 0 0 6.18M 0 00:07 00:07 8.63M
/root/ci_scratch/depends/work/download/native_qt-6.7.3/qtbase-everywhere-src-6.7.3.tar.xz.temp: OK
Fetching qttranslations-everywhere-src-6.7.3.tar.xz from https://download.qt.io/archive/qt/6.7/6.7.3/submodules
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 288 100 288 0 0 2234 0 0
100 1.47M 100 1.47M 0 0 532.5k 0 00:02 00:02 208.8k
/root/ci_scratch/depends/work/download/native_qt-6.7.3/qttranslations-everywhere-src-6.7.3.tar.xz.temp: OK
Fetching qttools-everywhere-src-6.7.3.tar.xz from https://download.qt.io/archive/qt/6.7/6.7.3/submodules
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 281 100 281 0 0 2156 0 0
100 8.60M 100 8.60M 0 0 1.27M 0 00:06 00:06 1.26M
/root/ci_scratch/depends/work/download/native_qt-6.7.3/qttools-everywhere-src-6.7.3.tar.xz.temp: OK
Fetching CMakeLists.txt from https://raw.githubusercontent.com/qt/qt5/refs/heads/6.7.3
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 4041 100 4041 0 0 23565 0 0
/root/ci_scratch/depends/work/download/native_qt-6.7.3/CMakeLists.txt-6.7.3.temp: OK
Fetching ECMOptionalAddSubdirectory.cmake from https://raw.githubusercontent.com/qt/qt5/refs/heads/6.7.3/cmake
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 3029 100 3029 0 0 16610 0 0
/root/ci_scratch/depends/work/download/native_qt-6.7.3/ECMOptionalAddSubdirectory.cmake-6.7.3.temp: OK
Fetching QtTopLevelHelpers.cmake from https://raw.githubusercontent.com/qt/qt5/refs/heads/6.7.3/cmake
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 21633 100 21633 0 0 118.6k 0 0
/root/ci_scratch/depends/work/download/native_qt-6.7.3/QtTopLevelHelpers.cmake-6.7.3.temp: OK
Extracting native_qt...
/root/ci_scratch/depends/sources/qtbase-everywhere-src-6.7.3.tar.xz: OK
/root/ci_scratch/depends/sources/qttranslations-everywhere-src-6.7.3.tar.xz: OK
/root/ci_scratch/depends/sources/qttools-everywhere-src-6.7.3.tar.xz: OK
/root/ci_scratch/depends/sources/CMakeLists.txt-6.7.3: OK
/root/ci_scratch/depends/sources/ECMOptionalAddSubdirectory.cmake-6.7.3: OK
/root/ci_scratch/depends/sources/QtTopLevelHelpers.cmake-6.7.3: OK
^Cmake: *** [funcs.mk:343: /root/ci_scratch/depends/work/build/x86_64-w64-mingw32/native_qt/6.7.3-3feee3a98ec/.stamp_extracted] Interrupt
make -C depends/ -j1 HOST=x86_64-w64-mingw32
make: Entering directory '/root/ci_scratch/depends'
Extracting native_qt...
/root/ci_scratch/depends/sources/qtbase-everywhere-src-6.7.3.tar.xz: OK
/root/ci_scratch/depends/sources/qttranslations-everywhere-src-6.7.3.tar.xz: OK
/root/ci_scratch/depends/sources/qttools-everywhere-src-6.7.3.tar.xz: OK
/root/ci_scratch/depends/sources/CMakeLists.txt-6.7.3: OK
/root/ci_scratch/depends/sources/ECMOptionalAddSubdirectory.cmake-6.7.3: OK
/root/ci_scratch/depends/sources/QtTopLevelHelpers.cmake-6.7.3: OK
mkdir: cannot create directory ‘qtbase’: File exists
make: *** [funcs.mk:343: /root/ci_scratch/depends/work/build/x86_64-w64-mingw32/native_qt/6.7.3-3feee3a98ec/.stamp_extracted] Error 1
make: Leaving directory '/root/ci_scratch/depends'
I've run into other similar issues in Qt, when a Guix build is killed/interrupted for some reason, and it's not possible to restart without manually cleaning up.