Why: the RDM materialization fix landed separately as PR #684, so this branch now takes main's version of the workflow and carries only the pin change. The conflict resolution keeps the fix (submodule update per pin, language-agnostic fail-loud assertion) and drops the pin-specific comment that described a first-parent distance belonging to the other pull request. Impact: workflow resolves to main's already-merged content; this commit's own contribution is the rdm.pin prev_sha correction. Refs: PR #682, PR #684