Deliver agent prompts reliably at launch

[exe-dev-github-integration]

Summary

• deliver initial prompts through a protected temporary file and a safe launch-time instruction
• trust only the isolated Codex run directory and bypass hook trust for unattended runs
• retain state-aware asynchronous prompting for recovery of existing sessions
• add an isolated fake-Herdr E2E test that executes the generated shell without a real agent or live Herdr state

Validation

• npm run check
• TypeScript, 86 unit tests, Worker E2E, isolated agent-launch E2E, and Wrangler dry-run all pass