make uatu copies the real fat JAR into assets/ before
go build -tags withsidecar. Keeping that path tracked was
the root cause of the 130 MB push rejection.
Splits embed.go so the go:embed directive only fires under
-tags withsidecar. Default builds get a stub with a nil JAR
and IsPlaceholder()=true. This removes the landmine where
make uatu overwrote a tracked placeholder file, making any
git add silently stage 130 MB.
Ships with a 24-byte placeholder so fresh clones build without
requiring a sidecar build first. `make uatu` copies the real
fat JAR into internal/sidecar/assets before `go build`, so
shipping binaries carry the full sidecar (~130 MB).
Extract writes the JAR to a temp dir alongside a SHA-256 file
and skips rewrite when the checksum already matches.
pj