Summary of Changes

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This pull request addresses an issue where freethreaded Python builds were being incorrectly selected and causing installation failures due to incompatible library paths. The changes modify the precompiled Python build selection logic to prioritize standard builds by default, ensuring a smoother installation experience for most users. Users who specifically require freethreaded builds can still opt into them via a configuration setting.

Highlights

• Python freethreaded build path issue: Freethreaded Python builds (e.g., cpython-3.14.3+20260320-x86_64-unknown-linux-gnu-freethreaded-install_only_stripped.tar.gz) incorrectly used lib/python3.14t/ instead of lib/python3.14/, leading to "Python installation is missing a lib directory" errors.
• Precompiled build selection logic: The previous ranking logic for precompiled Python builds treated freethreaded and non-freethreaded variants equally, with freethreaded builds sometimes being selected due to alphabetical sorting.
• Default freethreaded build exclusion: Freethreaded tarballs are now filtered out by default during precompiled build selection, unless the python.precompiled_flavor configuration is explicitly set to a freethreaded variant.

Greptile Summary

This PR fixes a regression where mise up --bump python could select freethreaded Python builds (e.g. cpython-3.14.3+20260320-...-freethreaded-install_only_stripped.tar.gz) by default, causing a "Python installation is missing a lib directory" error because freethreaded builds use lib/python3.14t/ rather than lib/python3.14/. The fix has two parts:

• python.rs: A single-line filter is added in both fetch_precompiled_remote_versions and fetch_precompiled_for_target to exclude lines containing freethreaded unless python.precompiled_flavor is explicitly set, preserving opt-in support for freethreaded builds.
• sysconfig/mod.rs: find_sysconfigdata is refactored to probe three lib-directory candidates in order — with suffix, without suffix, and with the t suffix — so that if a freethreaded build is explicitly installed via precompiled_flavor, sysconfig patching will still work correctly.

The approach is minimal and well-targeted. One concern: the static PRECOMPILED_CACHE in fetch_precompiled_remote_versions uses python_precompiled_platform() as its cache key, which produces the same string ({arch}-{os}) regardless of whether freethreaded entries are filtered. Users with an existing on-disk cache from before this fix will continue to see freethreaded versions until the cache TTL expires.

Confidence Score: 4/5

• Safe to merge; one concrete but non-blocking concern around stale on-disk caches that include freethreaded entries.
• The core filter logic is correct and directly addresses the reported bug. The sysconfig/mod.rs refactor is clean and handles the freethreaded lib-path edge case properly. The only substantive concern is that PRECOMPILED_CACHE uses the same disk-cache key before and after this fix, meaning existing users with a non-expired cache won't benefit until the TTL elapses. This is real but self-resolving and doesn't affect fresh installs. A one-line cache-key bump would fully resolve it.
• src/plugins/core/python.rs — specifically the PRECOMPILED_CACHE key at lines 162-168.

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[mise up --bump python] --> B[fetch_precompiled_remote_versions / fetch_precompiled_for_target]
    B --> C{precompiled_flavor set?}
    C -- Yes --> D[Pass all lines incl. freethreaded\nthrough platform filter]
    C -- No --> E[Filter out lines containing 'freethreaded']
    D --> F[Select best tarball via rank / min_by_key]
    E --> F
    F --> G[Download & extract tarball]
    G --> H[install_precompiled: call update_sysconfig]
    H --> I[find_sysconfigdata]
    I --> J{lib/pythonM.mt exists?}
    J -- Yes freethreaded --> K[Use lib/pythonM.Mt/]
    J -- No --> L{lib/pythonM.m exists?}
    L -- Yes --> M[Use lib/pythonM.m/]
    L -- No --> N[Error: MissingLib]
    K --> O[Patch _sysconfigdata_ file]
    M --> O

_{Last reviewed commit: "fix(python): handle ..."}

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