TestFx parallel-safety preflight

Run this during implementation, not only during review. Keep it bounded to the requested change and its reachable conflicts; do not turn it into a repository audit or speculative hardening.

Reuse the canonical analysis

Read .github/copilot-instructions.md, the owning project's configuration and BannedSymbols.txt when present, and .github/workflows/shared/parallel-safety-audit-shared.md. Apply the shared rubric from # Parallel-safety audit through Step 3, including its assembly-scoping rules. It owns scheduling semantics, the A-D taxonomy, severity, confidence, culture/ExecutionContext distinctions, and declaration reconciliation; do not duplicate or replace it.