Context

Implement inter-agent message bus per design spec sections 5.1 and 15.2. This is the foundational communication layer that all agent-to-agent messaging will be built upon.

Options to evaluate:

• asyncio queues — simplest, in-process, good for single-process deployment
• Redis Pub/Sub — external broker, supports multi-process deployment
• Custom event system — tailored to our needs, medium complexity

The initial implementation should use asyncio queues for simplicity, but the interface must be abstract enough to swap in Redis or another broker later.

Acceptance Criteria

• Abstract message bus interface defined (swappable implementations)
• In-process asyncio queue implementation as default backend
• Pub/sub with named channels (#engineering, #all-hands, etc.)
• Direct messaging between specific agents
• Message persistence (in-memory log with configurable retention)
• Message ordering guarantees (per-channel FIFO)
• Comprehensive unit tests (>80% coverage)
• Design allows future Redis Pub/Sub swap without changing consumers

Dependencies

• Depends on agent engine (Implement agent engine core with ExecutionLoop protocol integration (DESIGN_SPEC §3.1, §6.1, §6.5) #11)

Design Spec Reference

• Section 5.1 — Communication Patterns
• Section 5.4 — Channel Architecture