[Julio-Patron]

Summary

• replace the raw crates.io probe with a tested fail-closed helper
• send a repository-specific User-Agent required by the registry endpoint
• run the live, credential-free crates.io preflight in PR CI and release validation
• advance ses-core to 2.0.3 because PyPI releases are immutable

Evidence

• pytest -q tests/test_release_contract.py tests/test_check_crate_publication.py (9 passed)
• python scripts/check_crate_publication.py --version 0.1.0 --allow-missing (published version confirmed)
• python scripts/validate_release.py --tag v2.0.3 (passed)
• both workflow YAML files parse successfully
• git diff --check (passed)

Release history

• v2.0.1 and v2.0.2 remain immutable partial releases
• no historical tag is moved or reused