test(release-hygiene): permit and require skip-existing on pypi publish

The previous assertion "assert 'skip-existing' not in payload" was a strict
'never silently skip a publish' guardrail. It pre-dated the case where the
root colsearch package and the native crates (latence-shard-engine,
latence-solver) are versioned independently — colsearch 0.1.7 is a
metadata-only release for the natives (repo URL update only), so attempting
to upload native wheels at the unchanged 0.1.6 version returns 400 from
PyPI and (because publish-root needs publish-native) the colsearch root
publish gets skipped too. With skip-existing: true the asymmetric versioning
case is idempotent.

Flip the assertion: skip-existing: true MUST be present, with a comment in
the workflow explaining the policy. Also documents the second use case —
gh run rerun --failed after a partial publish needs skip-existing or every
already-uploaded wheel breaks the rerun.

All 14 oss-release-hygiene tests pass locally.

Author: ddickmann

tests/test_oss_release_hygiene.py

@@ -86,7 +86,17 @@ def test_release_workflow_only_builds_supported_native_wheels() -> None:
     assert "publish-root" in payload
     assert "packages-dir: dist-native/" in payload
     assert "packages-dir: dist-root/" in payload
-    assert "skip-existing" not in payload
+    # `skip-existing: true` is intentionally enabled on both pypi-publish
+    # steps. The native crates (latence-shard-engine, latence-solver) are
+    # versioned independently of the root colsearch package and only need a
+    # republish when their Rust source changes; a colsearch release that
+    # ships without a native bump (e.g. metadata-only changes like updated
+    # repository URLs) would otherwise hit "400 File already exists" on every
+    # native wheel and skip the colsearch root publish that follows. The flag
+    # is also load-bearing for `gh run rerun --failed` after a partial publish
+    # — without it, the rerun fails on every wheel that already landed in the
+    # first attempt. See ci(release) commit message for the full rationale.
+    assert "skip-existing: true" in payload
     assert "crate: hnsw_indexer" not in payload
     assert "crate: gem_router" not in payload
     assert "crate: gem_index" not in payload