Clean up temporary files when closing a rewrite fails - #721

Summary

Clean up the temporary file when rewrite() fails while closing its buffered output. The cleanup scope now includes the temporary-file context manager's exit, while preserving the original target and propagating the error.

A write can be buffered successfully and fail only during close (for example, when the filesystem reports a size limit). Previously, that exception escaped before _discard_temp_file(), leaving a partial .tmp_* file behind after set_key() or unset_key().

Changes

• Include close, mode restoration, and replacement in the existing best-effort cleanup scope.
• Keep temporary-file cleanup after the handle is closed.
• Add three close-failure regression cases for creating, updating, and deleting keys, plus two guards for ordinary exceptions and KeyboardInterrupt.
• Add a changelog entry.

Reproduction and related work

An isolated Linux subprocess with RLIMIT_FSIZE=3 and SIGXFSZ ignored reproduces a real close-time EFBIG without mocking file I/O. Creating a new file, updating an existing file, and removing a key each leave one partial temporary file on the base; this patch leaves none. The original target remains unchanged in all cases.

This extends the cleanup introduced in #686. It also covers a failure boundary still present with the flush/fsync change proposed in #717: a repeated buffered-write failure during context exit can escape its inner cleanup scope.

Validation

Against main at 0b2880591780a426b0551436f47a17e7a76d954f:

• Full unmodified baseline suite on Linux/Python 3.10, 3.12, 3.13, and 3.14: 288 passed per interpreter, zero skipped.
• Full patched suite on the same four interpreters: 293 passed per interpreter, zero skipped.
• Five added cases: three close-failure regressions fail on the base and pass with this patch; the two body-error guards pass on both.
• Ruff lint and format, mypy targets 3.10 through 3.14, pinned pre-commit hooks, check-manifest, strict MkDocs build, and isolated sdist/wheel build all pass.

Windows, PyPy, Python 3.11, and free-threaded runtime coverage are left to upstream CI; the local runtime results above are Linux only.

AI assistance: this patch, tests, and description were prepared and checked with OpenAI Codex. Submitted as a draft for human review.