build-appimage.sh now reads the binary from CARGO_TARGET_DIR when set, so a
broad-compat build inside an old-glibc distrobox can use an isolated target
dir without clobbering the host's. README documents the Ubuntu 24.04
distrobox recipe and why older bases don't work (the pipewire crate needs
PW >= ~1.0 headers; and a PipeWire/portal app can't run on ancient distros
anyway). Resulting baseline: glibc 2.39 (the only 2.39 symbols are weak
pidfd refs from Rust std; everything else is <= 2.35).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
mollusk
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