feat: inter-instance communication channel for dynamic coordination

[Iron-Ham]

Summary

Add a real-time message bus that allows Claude Code instances to dynamically communicate and coordinate during execution, going beyond the current static context.md approach.

Problem

Currently, instances only share context via a static context.md file generated at session start. They cannot:

• Share discoveries made during execution
• Claim "ownership" of files/modules to avoid conflicts
• Request help or delegate subtasks to other instances
• Coordinate on shared concerns in real-time

This leads to duplicate work and missed opportunities for collaboration.

Proposed Solution

Implement an inter-instance message bus with:

Message Types

• Discovery: "I found that auth uses JWT tokens in internal/auth/"
• Claim: "I'm working on internal/api/ - please avoid modifying"
• Release: "Done with internal/api/ - available for others"
• Question: "Does anyone know where the database config is?"
• Answer: "Database config is in internal/config/database.go"

Implementation Ideas

• Extend the existing internal/event/ bus with cross-instance messaging
• Use a shared file or socket for IPC between tmux sessions
• Inject received messages into each instance's context dynamically
• TUI panel showing recent cross-instance messages

Benefits

• Reduced duplicate work across instances
• Better coordination on complex multi-file changes
• Instances can learn from each other's discoveries
• More efficient use of API tokens

Alternatives Considered

• Periodic context.md regeneration: Simpler but not real-time
• Shared database: More complex infrastructure
• Direct Claude-to-Claude API calls: Not feasible with current architecture

Related

• feat: add shared context files for cross-instance coordination #30 (shared context files - static approach)
• Could integrate with conflict detector for automatic claims

[Iron-Ham]

Update: Superseded by Orchestration 2.0

This proposal has been superseded by a more comprehensive design in #629 (Inter-Instance Mailbox System), which is part of the Orchestration 2.0 initiative (#638).

The new design incorporates the ideas from this issue (discovery, claim, release, question, answer message types) and adds:

• Structured message schema with typed messages
• Broadcast and targeted messaging
• Integration with a broader collaborative orchestration architecture
• Foundation for Context Propagation (Epic: Context Propagation Between Instances #632) and File Conflict Prevention (Epic: Cross-Instance File Conflict Prevention #635)

See #638 for the full roadmap.