Restructure session.lock from command-wrapper flock to fd-based flock so
the lock can be released when Claude is idle and re-acquired before
injecting the next prompt.
- agent-session.sh: add session_lock_acquire/release helpers, open fd in
create_agent_session instead of wrapping claude with flock, auto-acquire
in agent_inject_into_session before injecting
- phase-handler.sh: call session_lock_release at start of awaiting_ci and
awaiting_review handlers (Claude is idle during CI polling / review wait)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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