[gaborbernat]

When a caller supplied an environment mapping without HOME or USERPROFILE, uv store discovery substituted ~ and expanded it from the process environment. Discovery could then execute a candidate in that process home even though the caller's mapping did not name the directory. Default uv roots now come only from the supplied mapping. This addresses draft advisory ANT-2026-XQVCZ8E5.

The home fallback escaped the mapping

Path.expanduser() resolves ~ to the process user's home. The old fallback used it when the mapping lacked a home variable, then probed executables under the resulting uv roots. The new selection skips home-derived roots when the mapping has no home variable.

flowchart LR
    M[Mapped home absent] --> O[Old: expand process home]
    O --> P[Probe process-home uv store]
    M --> N[New: skip home-derived roots]
    M --> D[Mapped data directory present]
    D --> R[Probe mapped uv store]
    classDef old fill:#ffd6d6,stroke:#c1121f,color:#5c0000;
    classDef fixed fill:#d8f3dc,stroke:#2d6a4f,color:#1b4332;
    class O,P old;
    class N,D,R fixed;

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Platform directory selection

uv uses platform data directories for managed Python installs. Windows still accepts an absolute mapped APPDATA; macOS and Linux still accept an absolute mapped XDG_DATA_HOME. The Windows profile default requires mapped USERPROFILE; Unix home defaults require mapped HOME. The platform branches use those values.

Behavior changes

An explicit mapping with only PATH no longer searches the process home for uv-managed interpreters. Calls that omit env still use the process environment as their mapping. An explicit UV_PYTHON_INSTALL_DIR still selects its own root. Fixes #200.

Reported by Anthropic's OSS Scanner: ANT-2026-XQVCZ8E5.