[Gastown] PR 16: Multi-Rig Support

[jrf0110]

Parent: #204 | Phase 3: Multi-Rig + Scaling

Revised: All rigs in a town share the same Town Container. Each rig's agents get their own git clones and worktrees inside the container.

Goal

A Town with multiple rigs, cross-rig mail routing, and the dashboard reflecting all rigs.

Changes

• Town DO maintains rig registry, routes cross-rig mail via Rig DO RPCs
• Dashboard shows all rigs in a town with drill-down
• Convoys can span multiple rigs
• Mayor can distribute beads across rigs based on rig capabilities/load
• All rigs in a town share the same container — each rig's agents get their own git clones and worktrees

Cross-Rig Mail Routing

When an agent in Rig A needs to communicate with an agent in Rig B:

1. Agent sends mail via gt_mail_send with target agent identity
2. Rig DO A forwards to Town DO
3. Town DO resolves target rig from agent identity
4. Town DO forwards to Rig DO B
5. Target agent receives on next gt_mail_check

Container Impact

Multiple rigs sharing one container means:

• Multiple git clones (one per rig) in /workspace/rigs/{rigId}/repo
• More worktrees, more processes
• Disk usage scales with number of rigs × repo size
• May need to scale to larger instance type or shard to container-per-rig for large towns

Dashboard Changes

• Town overview shows all rigs with summary stats
• Rig selector/navigation
• Cross-rig convoy view showing beads distributed across rigs

Dependencies

• PR 9 (Town DO)
• PR 10 (Multiple Polecats)
• PR 14 (Convoy Lifecycle)

Acceptance Criteria

• Town DO rig registry with add/remove
• Cross-rig mail routing via Town DO
• Multi-rig convoy support
• Dashboard multi-rig view with drill-down
• Mayor can distribute work across rigs
• Multiple rigs sharing container with isolated git clones