The initial startup already requires an the extensions symlink to be valid

start.sh

@@ -2,7 +2,7 @@
 
 set -eu
 
-mkdir -p /run/php/session
+mkdir -p /run/php/session /app/data/extensions
 
 if ! [ -f /app/data/.installed ]; then
     echo "==> Fresh installation, setting up..."
@@ -29,7 +29,6 @@ ln -s /tmp/log_api.txt /app/data/users/_/log_api.txt
 
 # We have to copy instead of symlinking extensions (see #2)
 echo "==> Copying packaged extensions"
-mkdir -p /app/data/extensions
 for f in $(ls /app/code/extensions-orig); do
     rm -rf "/app/data/extensions/$f"
     cp -r "/app/code/extensions-orig/$f" "/app/data/extensions"