handlePlan charged the budget but never checked the ceiling or set the flag, so a plan-ONLY stream kept emitting after crossing the cap (caught by both review bots). It now flags + truncates exactly like text/thinking. Adds the plan-only flood regression test (185 total) and the category frontmatter field to the new solutions doc. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>