fix: fail the release when the computed version already exists on the registry

[n24q02m]

Problem

PyPI never allows reusing a version number. If this repo's git history is ever rewritten away from what was published, python-semantic-release (PSR) can later compute an already-published version. Two bad outcomes follow:

• Silent freeze: if a matching git tag exists, PSR reports the version "already released", sets released=false, and the downstream publish-pypi job is silently skipped. Nobody notices.
• Opaque failure: if no tag exists, uv publish dies with an opaque 409 deep inside the pipeline, after PSR has already created a git tag and GitHub Release.

Neither is acceptable. This adds a loud, early, actionable failure instead.

Change (.github/workflows/cd.yml only)

Placed in the release job, before the real semantic-release step, so it fires before any tag or Release is created:

1. Dry-run step (id: dryrun) -- the exact same pinned PSR action (350c48fcb3ffcdfd2e0a235206bc2ecea6b69df0) with no_operation_mode: true (--noop) and the same prerelease/prerelease_token inputs as the real id: release step. This repo's real step passes no config_file, so the dry-run doesn't either -- both compute the version identically against the same untouched checkout. No new action or dependency.

2. Guard step -- gated on steps.dryrun.outputs.released == 'true' (mirrors the existing needs.release.outputs.released == 'true' gate on publish-pypi, so a "no releasable commits" dispatch doesn't false-fail on the current already-published version). Queries PyPI for qwen3-embed==<computed version> (name verbatim from pyproject.toml [project].name) and classifies:

   curl -o /dev/null -w '%{http_code}'	meaning	action
   200	COLLISION -- version exists	::error:: + exit 1
   404	FREE -- version/package absent	proceed
   anything else	UNKNOWN -- network/registry error	::error:: + exit 1, never treated as free

   I confirmed myself that PyPI normalizes the version string in the URL path: https://pypi.org/pypi/qwen3-embed/1.12.1-beta.1/json and https://pypi.org/pypi/qwen3-embed/1.12.1b1/json both return 200 for the same release, so PSR's raw semver version output can go straight into the URL without reformatting.

A transient error is deliberately treated as fatal rather than "free" -- reading it as free would let a real collision slip through, which is worse than the bug this guard prevents.

The release job's outputs (released/tag/version/is_prerelease) still come from the real id: release step and are unchanged, so publish-pypi, notify-downstream, create-downstream-issues consume them exactly as before.

Verification

YAML parses:

$ python -c "import yaml; yaml.safe_load(open('.github/workflows/cd.yml')); print('YAML OK: parsed successfully')"
YAML OK: parsed successfully

Guard's shell classification logic exercised live against the real PyPI registry, using the exact curl invocation from the guard, three ways:

CASE 1  version 1.12.1 (published)   -> http=200 -> CLASSIFICATION: COLLISION (fail, exit 1)
CASE 2  version 99.99.99 (unused)    -> http=404 -> CLASSIFICATION: FREE (proceed, exit 0)
CASE 3  forced-unreachable endpoint  -> http=000 -> CLASSIFICATION: UNKNOWN (fail, exit 1)

Commit created with pre-commit hooks running normally (the Python-only hooks -- ruff/ty/pytest -- correctly skip a YAML-only change).

Do not merge.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None