fix nix dl buffer thing

Author: prestoncabe

.devcontainer/Dockerfile

@@ -5,6 +5,13 @@ WORKDIR /code
 USER root:root
 RUN mkdir -p /code && chown ${DEVBOX_USER}:${DEVBOX_USER} /code
 USER ${DEVBOX_USER}:${DEVBOX_USER}
+
+# Work around Nix 2.30 download buffer bug (NixOS/nix#11728):
+# increase buffer from 64 MiB to 512 MiB and reduce concurrent downloads
+RUN mkdir -p ~/.config/nix && \
+    echo "download-buffer-size = 536870912" >> ~/.config/nix/nix.conf && \
+    echo "max-substitution-jobs = 4" >> ~/.config/nix/nix.conf
+
 COPY --chown=${DEVBOX_USER}:${DEVBOX_USER} devbox.json devbox.json
 COPY --chown=${DEVBOX_USER}:${DEVBOX_USER} devbox.lock devbox.lock
 COPY --chown=${DEVBOX_USER}:${DEVBOX_USER} .env.example .env