The runtime image carries only what serving needs — the Julia runtime, an
already-precompiled depot, exiftool, and optionally github-linguist. The
package registry, git clones, and the Ruby/C toolchain that builds rugged
all stay in earlier stages.
Two things shape the build. Dependencies are instantiated and precompiled in
a layer keyed only on Project.toml/Manifest.toml, so a src/ edit rebuilds in
seconds rather than minutes; a stub src/FileServer.jl satisfies Pkg's
root-package check there. And github-linguist, the one heavy optional
dependency, is behind WITH_LINGUIST: it degrades gracefully (stage 4 keeps
natural-language enrichment and warns), so building it out is a supported
~160MB saving.
All stage directories are pointed under /data via the FS_*_DIR variables so
one volume holds the whole in-flight working set, and data/ is excluded from
the build context.
Claude-Session: https://claude.ai/code/session_01KMNwyqLS3ns6uwWHGDGdAQ
