Routes 1.21.1 builds to NC1 (ffg-builder user) to work around
Vineflower -Xmx4G RAM requirement that exceeds Dev Panel capacity.
All other versions build locally.
- SSH keypair: /home/claude/.ssh/ffg_build_rsa
- NC1 user: ffg-builder (non-root, isolated)
- rsync source with --exclude build/ .gradle/
- ./gradlew build --no-daemon on NC1
- rsync jar back, jar -tf integrity check
- trap cleans workspace on exit/drop
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