Probe the Interpreter the Way the Host Contract Declares It

[ptr727]

Answers the suppressed finding on the promotion pull request #643, which cannot take a fix of its own since its head is develop.

The hook invokes python3 directly, but docs/host-setup.md notes that on native Windows the python.org install registers py (and python) but not python3, so this hook will fail for Windows contributors running Git hooks via Git Bash.

Accepted. This is the repository contradicting itself: docs/host-setup.md states the hazard in its own paragraph, and spec/host-tools.json already encodes the answer as its probe order, [["python3", "--version"], ["py", "-3", "--version"]]. The hook restated a name the contract says is wrong on one supported platform. It now follows the same order rather than naming an interpreter.

Checked on a PATH that has py and no python3

Rather than reasoning about Windows from Linux, the shape was reproduced: a PATH carrying git, sh and a stand-in for the Windows launcher, and no python3 at all.

$ PATH=$D command -v python3 || echo NO
NO
$ PATH="$D" sh .husky/pre-commit
[ok  ] eol          0 issue(s)
exit=0

The previous version on that same PATH:

$ PATH="$D" sh "$D/old-pre-commit"
old-pre-commit: 32: python3: not found
exit=127

So this fixes a real break rather than hardening against a hypothetical one. Worth being precise about the failure it was: exit 127 is non-zero, so the old hook blocked the commit rather than passing it falsely. The defect is that it was unusable on such a host, not that it was silently wrong.

With neither interpreter present

pre-commit: no python3 and no py -3 on PATH, so the doc gates did not run.
pre-commit: see docs/host-setup.md 'What a Host Must Provide'.
exit=1

It names what did not run and points at the contract, and exits non-zero. A hook that cannot run its gates must not report a clean commit, which is the same rule prose_lint.py follows when it announces a dropped rule rather than going quiet.

Verification

552 tests pass, prose_lint.py with the CI check list exits 0, and repo_gate.py reports eol, eol-coverage and sha-pin clean. The hook ran on this commit.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Updates the repo’s local pre-commit hook to select a Python interpreter in the platform-aware order declared by the host contract, so the hook remains usable on native Windows setups where python3 may be absent.

Changes:

• Adds interpreter selection logic to prefer python3 and fall back to py -3 when needed.
• Routes the prose and EOL checks through the selected interpreter.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.