PR #26998 evidence: fx compatibility revival

Evidence for pingdotgg#26998. Not a software release.

Current local validation receipts for head eb8b52d, with failing-before regressions and an ACP mock runtime receipt. Historical real-fx evidence remains labeled in the PR description. No new UI captures or paid provider turns.

Continued in replacement pingdotgg#29399 because GitHub refused to reopen the original PR.