uvx not downloaded when uv version already matches, leaving bin/uvx dangling

[oliver-cieliszak-natterbox]

TLDR

_bootstrap_uv decides whether to download by checking uv's version only. If prefix/uv already matches the pinned version but prefix/uvx is missing, uvx is never fetched - yet setup.py still creates bin/uvx -> ../uvx, leaving a dangling symlink and a broken $..._UVX env var. Reported as an observation from an upgrade path, not a live outage.

Reproduction (confirmed)

$ # a prefix whose uv already matches the pin, but with no uvx
$ rm -f "$PREFIX/uvx" "$PREFIX/bin/uvx"
$ ./install.sh --prefix "$PREFIX" --python 3.14 --env-prefix NATTERBOX --isolated
  ✓ uv 0.10.12            <- download skipped
  ✓ bin/uvx → ../uvx      <- symlink created anyway

$ ls "$PREFIX/uvx"
ls: no such file or directory

$ source "$PREFIX/env.sh" && "$NATTERBOX_UVX" --version
bash: .../uvx: No such file or directory

The install reports success throughout. Nothing warns that uvx is missing.

Cause

install.sh _bootstrap_uv (and the equivalent block in install.ps1):

if [[ -x "$uv_bin" ]] && \
   [[ "$("$uv_bin" --version 2>/dev/null | awk '{print $2}')" == "$uv_version" ]]; then
    _msg "  ✓ uv $uv_version"; return
fi

The guard predates uvx (added in v0.10.0, #4) and was never extended to account for the second binary. _create_bin in setup.py then unconditionally symlinks bin/uvx, so a missing uvx becomes a dangling link rather than an error.

When it bites

Upgrading from a pre-v0.10.0 prefix (no uvx) to a version that pins the same uv release the prefix already has. The version check short-circuits, uvx is never downloaded, and the resulting install looks healthy but has a broken uvx.

Not currently reachable via the Atlas bootstrap - v0.9.2 pins uv 0.10.6 and v0.11.0 pins 0.10.12, so uv is re-downloaded and uvx arrives with it (verified). It becomes reachable the moment a distro bump keeps uv_version unchanged, which is a perfectly normal thing to do.

Suggested fix

Extend the skip condition to require both binaries, so a missing uvx forces the download:

if [[ -x "$uv_bin" ]] && [[ -x "${prefix}/uvx" ]] && \
   [[ "$("$uv_bin" --version ...)" == "$uv_version" ]]; then

Same change in install.ps1 for uv.exe / uvx.exe. Optionally, have _create_bin warn (or fail) when a symlink target does not exist - a broken bin/ entry is never a valid outcome.

Reversibility

Two-way door - one guard condition per installer script.

Note

Found while bumping the Atlas install-dev-machine pin to v0.11.0 (redmatter/atlas#677). Filing rather than fixing, since it is outside that task's scope.