instant (dev) sandbox (#171)

* instant (dev) sandbox

* leave Dockerfile as is to pass deploy test

* fix comma

* fix prod build

* do not use "images exists" which docker does not support

* separate dev-mode flag

* Merge remote-tracking branch 'origin/main' into instant_sandbox

scripts/build.sh

@@ -25,6 +25,7 @@ npm run build --workspaces
 
 # also build container image if sandboxing is enabled
 # skip (-s) npm install + build since we did that above
+# use (-d) for dev build that can reuse existing image
 if scripts/sandbox_command.sh -q; then
-    scripts/build_sandbox.sh -s
+    scripts/build_sandbox.sh -sd
 fi