fix(sandbox): consolidate dev and prod sandbox (#273)

scripts/build.sh

@@ -25,7 +25,6 @@ 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 -sd
+if scripts/sandbox_command.sh -q && [[ "${BUILD_SANDBOX:-}" =~ ^(1|true)$ ]]; then
+    scripts/build_sandbox.sh -s
 fi