This shell script demonstrates a configuration-merging workflow for JSON files, specifically showing how to overlay or combine settings from a source file onto a target file. The code defines a `merge_config_json` function that takes two file paths and uses the `jq` command-line JSON processor with the `-s` (slurp) flag and the multiplication operator (`*`) to deeply merge the source object into the target object. If the target file does not exist, the script falls back to copying the source directly. The function relies on standard shell utilities (`mktemp`, `cp`, `mv`, `rm`) to handle temporary files and atomic replacement.