Build system: parameterize source maps

Sometimes, we get LavaMoat-related behavioral differences in production vs. development builds. It would be useful to parameterize source map inclusion, so that production builds are easier to debug.

The issue identifies the build system and LavaMoat-related differences but names no files or tests. Start by locating the production and development build configuration and the existing source-map handling, then compare their behavior. Done means source-map inclusion can be parameterized so production builds are easier to debug without changing the intended development behavior.

Written by the indexing model from the issue text.