ci: validate release artifacts before publishing

[igorls]

Summary

• run the release build and artifact validation on release-workflow pull requests and manual dispatches
• exercise upload-artifact v7 and download-artifact v8 before merging their upgrades
• verify archive contents and generate SHA256SUMS without publishing
• keep GitHub release creation restricted to v* tags with write permission scoped to that job

Validation

• git diff --check
• GitHub Release workflow is the authoritative end-to-end validation for all five target artifacts

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-31T11:06:54.289060Z	189d726	New commits

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