test(e2e): live validation of ACP agents, docs and ADR acceptance #67

Parent

#62

What to build

Validate the whole change live, and update the docs.

• Live leg, written up as a finding:
  • implement-parent-issue, or another real multi-step workflow, on Claude and on opencode,
    through factory serve and the UI;
  • an opencode permission ask outside the project (external_directory);
  • an agent crashing mid-turn (kill the process);
  • a RUN_ERROR from an agent;
  • cancel from the UI;
  • two concurrent runs, one per agent.
• Docs:
  • AGENTS.md: the preferred opencode test model is opencode/big-pickle; mention Claude.
  • The factory init template comments.
  • Site docs: workflow authoring (agent, model), config (agent.default, models,
    hostSettings), and the requirements (opencode on PATH, Claude login).
• ADRs: set ADR 0013 to Accepted and amend it if implementation changed anything. Add status
  notes to ADR 0007 (superseded) and ADR 0012 (§3/§6 amended).

Acceptance

• The finding is written, and every scenario passed or has an issue filed.
• Docs updated. bun run check green.