HCT A2A Extension

Harmonic Coordination Theory extension for Google A2A Protocol

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Overview

This extension adds coordination semantics from Harmonic Coordination Theory to the Agent-to-Agent (A2A) Protocol. It allows agents to coordinate using musical signals like cue, fermata (hold), and vamp (loop), and control resource intensity via dynamics.

Extension Registration

{
  "extensions": [
    {
      "uri": "https://github.com/stefanwiest/hct-a2a",
      "description": "HCT coordination signals for multi-agent orchestration"
    }
  ]
}

Specification

The canonical signal definition is provided in Protocol Buffers format, auto-generated from the central hct-spec.

• spec/v1/hct.proto - Protobuf Definition
• spec/v1/spec.md - Human Printable Spec and Schema

Polyglot Samples

We provide reference implementations demonstrating the Conductor/Performer relationship in four languages:

Language	Path	Concepts
Python	samples/python	Full Conductor/Musician, tempo, dynamics
TypeScript	samples/ts	Node.js asynchronous actors, vamp, attacca
Rust	samples/rust	High-performance Tokio tasks, type-safe signals
Go	samples/go	Struct-based Orchestration, fermata, caesura

Signals Reference

Signal	Description	A2A Method
cue	Trigger agent activation	tasks/send
fermata	Hold for approval	tasks/sendSubscribe
attacca	Immediate transition	tasks/send
vamp	Repeat until condition	tasks/sendSubscribe
caesura	Full stop	tasks/cancel
tacet	Agent inactive (A2A only)	—
downbeat	Global sync point (A2A only)	notifications/message

Canonical Source

Signal definitions are derived from:

• Source of Truth: hct-spec/spec.yaml

Related

• hct-mcp-signals - MCP extension (Python, npm, Rust, Go)
• A2A Protocol

License

Apache License 2.0