Pin every third-party GitHub Action to its current commit SHA with a
version comment, eliminating supply chain risk from mutable version
tags. Mutable tags (v4, v2, etc.) can be force-pushed by upstream
maintainers; SHA digests are immutable.
18 unique actions pinned across 9 workflow files.
Closes#357
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>