Codespaces (conda): Fix No space left on device

.devcontainer/onCreate-conda.sh

@@ -1,10 +1,26 @@
 # Do not keep running on errors
 set -e
+# Show commands run
+set -x
 
 # Create conda environment
-conda install mamba -n base -c conda-forge -y
+# A space bottleneck occurs at build time of the container
+# when the smallest (2-core, 32 GB) configuration is used.
+mkdir /tmp/conda-pkgs && mkdir -p /opt/conda && ln -s /tmp/conda-pkgs /opt/conda/pkgs
+conda install --quiet mamba -n base -c conda-forge -y
+# The following line shows the available space.
+# At the time of writing:
+# Filesystem      Size  Used Avail Use% Mounted on
+# overlay          32G   23G  7.5G  76% /
+# /dev/sda1        44G   52K   42G   1% /tmp
+# The 7.5G (also shared with /workspaces) are not enough for our
+# conda packages, which is why we redirect them into /tmp
+df -h / /tmp
 mamba env create --file src/environment-dev-3.11-linux.yml || mamba env update --file src/environment-dev-3.11-linux.yml
 conda init bash
+df -h / /tmp
+mamba clean --all --quiet --yes
+df -h / /tmp
 
 # Build sage
 conda run -n sage-dev ./bootstrap