GeezerVison

Summary

• Restore CPython 3.15 test_free_threading.test_capi through scripts/update_lib, retaining its canonical class/method/assertions and 10 × 4 concurrent-call loop.
• Make PyImport_AddModuleRef use an atomic exact-dict VM helper: return the insertion winner, conditionally replace non-modules by identity, and re-probe after a lost race. Module creation and reference destruction stay outside dict payload locks. Dict subclasses keep their callback dispatch; non-dict sys.modules support is unchanged.
• Add an explicit, generic migrate --new-file-adaptations path for introducing reviewed import/binding adapters into a previously absent canonical file. Exact source SHA, normalized target, unique non-overlapping source blocks, protected AST, and exclusive destination creation are required. Ordinary migration defaults remain unchanged.

The sole capability adapter uses existing support.get_attribute for an absent executable C API export. It does not skip supported-but-broken implementations or alter the test body. This does not duplicate #9270's CI/Windows-export changes.

Validation

• Host updater suite: 233 tests passed, including metadata/path/hash/block/AST/symlink/overwrite rejection coverage.
• Ruff formatting/check and diff whitespace checks passed.
• Linux CAPI-enabled locked/offline Cargo check and strict Clippy (-D warnings) passed, with actual VM opt-level 3 invocations.
• Linux CAPI-enabled CLI build passed. ELF export is defined FUNC GLOBAL DEFAULT PyImport_AddModuleRef; independently bound static loader closure excludes shared libpython.
• Canonical test: pinned CPython d220409a free-threaded reference and corrected RustPython each ran exactly one test with zero skips/failures/errors. Original 10 × 4 body was unchanged. FT GIL state stayed disabled before/after ctypes/support imports and the test, without forcing a GIL override. Owned process/thread cleanup and source/artifact snapshots were checked.
• Actual updater generation replay matched bytes; canonical class/function AST matched pinned CPython.

Limits

One bounded canonical concurrency test is not proof of all interleavings or complete CPython C API compatibility. Non-module/subclass/generic-mapping runtime corner cases were not exercised. Generic mappings remain unsupported. Exportless builds report a capability skip, not native validation; Windows export completeness is separate (#9270).

Validated locally on Linux against main 713e14cfc78d06372c68a1804240de52a8340548. Full workspace/crate-local CAPI suites and macOS/Windows execution were not run; the native behavioral check was intentionally restricted to the unchanged canonical method.

AI assistance

OpenAI Codex assisted with source investigation, implementation, updater migration, test orchestration, and independent agent review. The validation above was actually executed in the Linux environment; this does not claim human manual verification or validation on untested platforms.