docs: ADR-014 — Inter-agent communication patterns

[scottschreckengaust]

Summary

Define the communication protocol between development-time agents operating in different roles (Planner, Implementor, Reviewer per ADR-009).

Context

• ADR-009 establishes role boundaries but intentionally defers the communication mechanism
• PR docs: ADR-005 through ADR-013 (feedback, flags, knowledge, DoD, security, recovery, conflicts, knowledge stack, validation pyramid) #144 review identified this gap (reviewer @scoropeza, confirmed by @scottschreckengaust)
• Current state: single-agent-per-task model with no inter-agent communication

Scope

• Event-based communication model (asynchronous, not direct messaging)
• Modalities: GitHub issue/PR comments, EventBridge events, TaskEventsTable entries
• Discovery: agents discover work via issue assignment, not peer-to-peer negotiation
• No direct agent-to-agent messaging (avoids coupling and race conditions)

Dependencies

• ADR-009 (role boundaries — prerequisite, established)
• ADR-003 (governance — issue-based coordination)
• ADR-012 (operational knowledge stack — enforcement layer)

Acceptance criteria

• ADR-014 draft with status proposed
• Communication modalities documented with pros/cons
• Interaction patterns for common multi-agent workflows (plan → implement → review)
• Amend ADR-009, ADR-003 as needed after ADR-014 is accepted