feat(engine): add Codex, Droid, and Pi cli-agent adapters (U5)
Codex (hybrid tier): native done via session-scoped notify config,
heuristic PTY waiting detection, codex resume <thread-id>, probed rollout
JSONL tailer. Droid (native tier): Claude-style hooks with a Notification
permission-vs-idle classifier, --resume / exec -s resume (never -r in exec
mode). Pi (native tier): session-JSONL telemetry + transcript tailing,
pi --session resume. Adds the session-jsonl transcript source.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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