gt costs record now auto-detects the current tmux session when
running inside tmux, so the Stop hook no longer requires --session
flag or GT_SESSION env var.
Detection order:
1. --session flag
2. GT_SESSION env var
3. GT_RIG/GT_ROLE derivation
4. Current tmux session (new)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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