Proves that spawning `claude -p` in a pseudo-terminal from Rust gets Max
subscription billing (apiKeySource: "none", rateLimitType: "five_hour")
instead of per-token API charges. Concurrent agents run in parallel PTY
sessions with session resumption via --resume for multi-turn conversations.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
