[mihir-s-05]

Change and mathematical scope

When the Git --batch -z probe exits before its first stdin write on native Windows, CPython can raise OSError(EINVAL) at flush and again at close. The current reader handles only BrokenPipeError, so the older-Git fallback aborts before reading any pinned source.

Recognize this closed-stdin error only on Windows, at the request and cleanup boundaries. The existing first-request/no-response/exit-129 retry gate, exact blob validation and one-pass iterator remain intact. Other errors still propagate, and a failed legacy reader cannot trigger a third process.

Three files: the small reader fix, six behavioral tests, and a source/evidence note. Tooling only; no changed source pins, frozen packages, selected frontier or new κ.

Task and overlap

• Base/current canonical main: b58ad9ef4d4e861b0eaa5dba41742bdc072dca51, priority revision 7.
• Publication head: de93ebd044d0b00a8647a9f47f86939a6b18b9aa.
• portable-replay, scope changed from regenerated-payload comparison to a reproduced platform failure in immutable-source verification. Picker seed and bounded question/stop rule are in the note.
• Canonical claim and handoff: Discussion #4681.
• Builds on Nick Petalas's merged fix(replay): support source-pin checks on older Git #2752, head 73406fd73ebaf8361b51674fad5e0b02a26db075, which explicitly left Windows untested.
• Refreshed overlap: 450 open PRs, 3,612 Discussion records, plus all 5,860 tracked in-scope local notes. Exact error/path searches found no competing repair. Arbitrary diffs, closed remote PRs and unpublished work remain outside that coverage.
• Make committed-export regression fixtures portable to Windows #4579/Run real-Git drive-path export tests on Windows without skips #4679 repair exporter fixtures; the active Windows isolated-test lifetime claim in DONE: Linux/POSIX portability audit and descendant cleanup regression #1472 concerns a different launcher.

Validation

Before: the unchanged native compatibility module reports eight passes, one error and one existing CR/LF-path skip. Its exited-child test produces the real Windows errno-22 failure. The final six new tests against an exact copy of the base reader produce eight error subcases.

After, with -W error -B, both ordinary and optimized -O runs:

Environment	Scope	Result per mode
Windows / CPython 3.12.0 / Git 2.47.1.windows.1	Git batch, compatibility, new pipe errors, replacement refs, committed bytes, source history	51 passed, one existing CR/LF-path skip
Ubuntu under WSL / CPython 3.12.3 / Git 2.43.0	Git batch, compatibility, new pipe errors	23 passed, no skips

The unchanged registered compatibility hook also passes metadata/pins and all 38 currently discovered Git-reader tests on Linux:

python3 -W error -B scripts/research_package.py --package research/git-batch-compatibility

The new tests cover write/flush/close errors, binary/empty/duplicate blobs, independent object IDs, single iterator consumption, closed streams and reaped children. EIO, POSIX EINVAL, exit 0/7, post-response failure and legacy-reader failure remain rejecting controls. Only option rejection and the injected error variants are simulated; real Git supplies successful fallback bytes. git diff --check passes.

The shared-control planner selects all 2,480 registered packages. Its policy is unchanged; those broader scientific replays were not run locally. An initial broader Windows onboarding run hit existing fixture errors and was stopped; the sparse selected baseline also lacked its complete input closure. No complete onboarding, selected cold replay or hosted CI pass is claimed.

Credit

Nick Petalas (#2752) supplied the fallback and original tests; Douglas Colkitt the runner contracts; Arham Tahir the NUL pin batching; Woklerx the streamed-reader and cleanup lineage. Maxime Fleury's reproducibility work and the original P104/Abhinav Ramachandran reports retain their credit.

Prepared for Mihir Srivastava with substantial OpenAI Codex assistance, one agent. Apache-2.0.

Open next questions

Run the three reader modules against an actual older Git for Windows in a disposable fixture. That binary is not installed here; this repair uses the predecessor's controlled unsupported-option probe. Synchronous pipe-read deadlines and arbitrary Git/Python-version support remain separate obligations.