prepare records an immutable manifest of every regular backend/dist file
(path/size/sha256/dev/ino) in the owned root and binds its record identity
in ownership; serve revalidates record and every file before spawn, passes
the manifest to the child on fd 4, and the immutable preload hash-verifies
all files at startup and serves only cached verified bytes for any import
below backend/dist, so imported dependency replacement is refused before
RUNNING or never executes. The render command validates the commit
snapshot.json manifest, binds snapshot bytes to the manifest digest and the
installed Git blob, and passes the expected digest to the renderer, which
revalidates head/files digest with bounded no-follow reads and renders only
verified bytes with lease release on refusal.