Fans the security fix from internal#116 (cce89067) to molecule-core. Same
rationale: pull_request loads workflow from PR HEAD, allowing any
write-access contributor to rewrite the workflow file in their PR and
exfiltrate SOP_TIER_CHECK_TOKEN. pull_request_target loads from base
(main), neutralising the attack.
Verified post-merge on internal: synthetic PR rewriting the workflow to
print the token did NOT execute the modified version — main's
pull_request_target version ran instead. ATTACK_PROBE never fired.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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