Create ephemeral agent beads for ZFC-compliant polecat state tracking.
- Add AgentFields struct and helpers to beads package
- CreateAgentBead: Creates agent bead with role_type/rig/agent_state
- UpdateAgentState: Updates agent_state and hook_bead fields
- DeleteAgentBead: Hard-deletes ephemeral agent bead
- GetAgentBead: Retrieves and parses agent bead
- Integrate lifecycle in polecat manager:
- Add(): Creates gt-polecat-<rig>-<name> bead with state=spawning
- Recreate(): Deletes old bead, creates fresh with state=spawning
- RemoveWithOptions(): Deletes agent bead on nuke
This enables Witness to read polecat state from beads instead of
tmux scraping. State updates (spawning→working→done) are done by
polecats via bd agent state (separate beads CLI enhancement).
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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