Per-challenge WB205, with an ID transition plan first (STD-04 / OPEN-02) #61

Deferred from the 2026-09-30 standards review (#57); see design/2026-09-30-claude-standards-handoff.md and design/2026-09-30-rule-schema-help-proposal.md.

WB205 compares challenge and solution totals across an episode, so two solutions for challenge A hide challenge B having none (the explanation now says so).

Before replacing it with a per-challenge check, design the ID transition: one aggregate finding becomes several, and old ignores and filed issues (open or closed) must neither suppress unrelated new findings nor be silently dropped. Then handle nested callouts, multiple and floating solutions, discussion exercises, and guidance-instead-of-solution.