Block U follow-up: assistant-name dotfiles and /ai.json residuals

Same generator returned 2026-09-06T02:41:42Z, 33 min after the Block U deploy. The sweep confirms the arm on rows: every path from the 22:58 sweep is absent and only 4 residuals paged instead of 30. The four are the same family via shapes the first pass missed - vendor name as a bare dotfile (/.openai, /.anthropic), the suffixed /.cursorrules (the [/.] boundary correctly refused it), and /ai.json (the exact set carried ai_config, not bare ai).