The missing-script branch now fails in block mode instead of passing, the shell
block parses, the version walk refuses a directory it cannot read or one that
holds no manifest, the install is watched before anything else can throw, and a
spec runs `bash -n` over every Policy shell block.
`Policy / Pre-Merge Check` now runs `scripts/pre-merge-check.ts` under plain
Node and knows nothing else about the merged tree. That script installs the
dependencies, checks that every released manifest carries the root version
while the install runs, and builds the Host and Client contracts, reporting
which step failed.
imccyu