Assemble a distribution zip from a local source dir or a fetched ref.
SIDE EFFECTS: writes the zip at opts.Out; when fetching, clones over the network into a temp dir that is always cleaned up.
opts.Out
If neither SourceDir nor Ref is provided, or if fetch/assembly fails.
SourceDir
Ref
Assemble a distribution zip from a local source dir or a fetched ref.
SIDE EFFECTS: writes the zip at
opts.Out; when fetching, clones over the network into a temp dir that is always cleaned up.