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systemprompt-agent

Agent-to-Agent (A2A) protocol implementation for systemprompt.io AI governance: JSON-RPC models, task lifecycle, .well-known discovery, SSE streaming, governed agent orchestration, skill injection, and MCP tool integration.

Layer: Domain — business-logic modules built on shared/* and infra/*. Part of the systemprompt-core workspace.

Overview

Capabilities · Closed-Loop Agents

This crate implements the Agent-to-Agent (A2A) protocol and exposes:

A2A Server: JSON-RPC 2.0 message handling with SSE streaming
Agent Orchestration: Subprocess lifecycle, health monitoring, port allocation, state reconciliation
Context Management: Conversation contexts with task, message, and artifact persistence
Skill Service: Skill loading and per-request injection into agent prompts
MCP Integration: Tool execution results transformed into A2A artifacts
Registry: Agent card discovery and security metadata

HTTP routing lives outside this crate. API consumers compose AgentHandlerState and AgentServer from the services::a2a_server module into their own Axum router (typically in systemprompt-api).

Architecture

┌─────────────────────────────────────────────────────────────┐
│                      Services Layer                          │
│  ┌─────────────┐  ┌──────────────┐  ┌───────────────────┐   │
│  │ A2A Server  │  │ Orchestrator │  │ External Integr.  │   │
│  │  - auth     │  │  - lifecycle │  │  - webhooks       │   │
│  │  - handlers │  │  - monitor   │  │                   │   │
│  │  - processing│ │  - port mgr  │  ├───────────────────┤   │
│  │  - streaming│  │  - reconciler│  │       MCP         │   │
│  └─────────────┘  └──────────────┘  │  - tool results   │   │
│  ┌─────────────┐  ┌──────────────┐  │  - artifact xform │   │
│  │   Context   │  │   Registry   │  └───────────────────┘   │
│  │   Service   │  │  (cards +    │  ┌───────────────────┐   │
│  │             │  │   skills +   │  │     Skills        │   │
│  │             │  │   security)  │  │  - SkillService   │   │
│  └─────────────┘  └──────────────┘  │  - SkillInjector  │   │
│                                     └───────────────────┘   │
└─────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────┐
│                    Repository Layer (SQLX)                   │
│  ┌─────────────┐  ┌──────────────┐  ┌───────────────────┐   │
│  │    Task     │  │   Context    │  │     Content       │   │
│  │  - queries  │  │  - messages  │  │   - artifacts     │   │
│  │  - mutations│  │  - parts     │  │   - push notif    │   │
│  │  - constructr│ │  - notifs    │  │                   │   │
│  └─────────────┘  └──────────────┘  └───────────────────┘   │
│  ┌─────────────┐  ┌──────────────┐                          │
│  │  Execution  │  │ AgentService │                          │
│  │  steps      │  │              │                          │
│  └─────────────┘  └──────────────┘                          │
└─────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────┐
│                      Models Layer                            │
│  ┌─────────────┐  ┌──────────────┐  ┌───────────────────┐   │
│  │    A2A      │  │   Domain     │  │      Web          │   │
│  │  - protocol │  │   - context  │  │   - validation    │   │
│  │  - jsonrpc  │  │   - runtime  │  │   - queries       │   │
│  │  - status   │  │   - rows     │  │   - card input    │   │
│  └─────────────┘  └──────────────┘  └───────────────────┘   │
└─────────────────────────────────────────────────────────────┘

Usage

[dependencies]
systemprompt-agent = "0.13.0"

Directory Structure

src/
├── lib.rs                          # Crate root, public re-exports, A2A_PROTOCOL_VERSION
├── error.rs                        # AgentError, ArtifactError, ContextError, ProtocolError, RowParseError, TaskError
├── extension.rs                    # AgentExtension (Extension trait impl, schema registration)
├── state.rs                        # AgentState container
│
├── models/                         # Data structures
│   ├── mod.rs
│   ├── agent_info.rs               # AgentInfo
│   ├── context.rs                  # UserContext, ContextStateEvent
│   ├── database_rows.rs            # SQLX row structs
│   ├── external_integrations.rs    # Integration payload types
│   ├── runtime.rs                  # AgentRuntimeInfo
│   ├── a2a/
│   │   ├── mod.rs
│   │   ├── jsonrpc.rs              # JSON-RPC 2.0 envelope types
│   │   ├── service_status.rs       # Service status extension
│   │   └── protocol/
│   │       ├── mod.rs              # Task, Message, Artifact, Part, AgentCard
│   │       ├── events.rs           # Streaming event types
│   │       ├── push_notification.rs
│   │       └── requests.rs         # A2A method param types
│   └── web/
│       ├── mod.rs
│       ├── card_input.rs           # Agent card input validation
│       ├── create_agent.rs         # CreateAgentRequest
│       ├── discovery.rs            # Discovery types
│       ├── query.rs                # Query parameters
│       ├── update_agent.rs         # UpdateAgentRequest
│       └── validation.rs           # URL validation
│
├── repository/                     # Database access (SQLX macros only)
│   ├── mod.rs                      # A2ARepositories aggregate
│   ├── agent_service/mod.rs        # AgentServiceRepository
│   ├── content/
│   │   ├── mod.rs                  # ArtifactRepository re-export
│   │   ├── push_notification.rs    # PushNotificationConfigRepository
│   │   └── artifact/
│   │       ├── mod.rs
│   │       ├── converters.rs
│   │       ├── mutations.rs
│   │       ├── parts.rs
│   │       └── queries.rs
│   ├── context/
│   │   ├── mod.rs                  # ContextRepository
│   │   ├── mutations.rs
│   │   ├── notifications.rs
│   │   ├── queries.rs
│   │   └── message/
│   │       ├── mod.rs
│   │       ├── parts.rs
│   │       ├── persistence.rs
│   │       └── queries.rs
│   ├── execution/
│   │   ├── mod.rs                  # ExecutionStepRepository
│   │   └── parse.rs
│   └── task/
│       ├── mod.rs                  # TaskRepository
│       ├── mutations.rs
│       ├── queries.rs
│       ├── task_messages.rs
│       ├── task_updates.rs
│       └── constructor/
│           ├── mod.rs              # TaskConstructor
│           ├── batch.rs
│           ├── batch_builders.rs
│           ├── batch_queries.rs
│           ├── converters.rs
│           └── single.rs
│
└── services/                       # Business logic
    ├── mod.rs                      # Service re-exports
    ├── artifact_publishing.rs      # ArtifactPublishingService
    ├── context.rs                  # ContextService (history loading)
    ├── context_provider.rs         # ContextProvider trait impl
    ├── execution_tracking.rs       # ExecutionTrackingService
    ├── message.rs                  # MessageService
    ├── registry_provider.rs        # AgentRegistryProvider trait impl
    │
    ├── a2a_server/                 # A2A protocol server
    │   ├── mod.rs
    │   ├── server.rs               # AgentServer
    │   ├── standalone.rs           # Standalone agent runner
    │   ├── auth/                   # JWT validation + middleware
    │   ├── errors/                 # JSON-RPC error mapping
    │   ├── handlers/               # card, push_notification_config, request routing
    │   ├── processing/             # ai_executor, conversation, message, strategies, task_builder, artifact
    │   └── streaming/              # SSE event loop, broadcast, webhook client
    │
    ├── agent_orchestration/        # Agent lifecycle
    │   ├── mod.rs
    │   ├── database.rs             # Orchestration state persistence
    │   ├── event_bus.rs            # AgentEventBus
    │   ├── events.rs               # AgentEvent
    │   ├── monitor.rs              # Health probing
    │   ├── reconciler.rs           # DB ↔ process reconciliation
    │   ├── lifecycle/              # State machine + verification
    │   ├── orchestrator/           # AgentOrchestrator, cleanup, daemon, status
    │   ├── port_manager/           # Dynamic port allocation + probe
    │   └── process/                # Subprocess command + signal handling
    │
    ├── external_integrations/      # External service integrations
    │   ├── mod.rs
    │   └── webhook/                # WebhookService (delivery, types)
    │
    ├── mcp/                        # MCP tool integration
    │   ├── mod.rs
    │   ├── tool_result_handler.rs
    │   ├── artifact_transformer/   # Tool result → A2A artifact (metadata, parts, type inference)
    │   └── task_helper/            # Task completion + message helpers
    │
    ├── registry/                   # Agent registry
    │   ├── mod.rs                  # AgentRegistry (card loading)
    │   ├── security.rs             # Security metadata
    │   └── skills.rs               # Skill registration
    │
    ├── shared/                     # Cross-service utilities
    │   ├── mod.rs
    │   ├── auth.rs
    │   ├── config.rs
    │   ├── error.rs
    │   ├── resilience.rs
    │   └── slug.rs
    │
    └── skills/                     # Skill management
        ├── mod.rs
        ├── skill.rs                # SkillService
        └── skill_injector.rs       # SkillInjector

Schemas

Schemas live in schema/ and are registered via AgentExtension:

File	Purpose
`agent_tasks.sql`	Task records
`artifact_parts.sql`	Artifact part rows
`context_agents.sql`	Context-to-agent associations
`context_notifications.sql`	Per-context push notification config
`message_parts.sql`	Message part rows
`services.sql`	Service registry
`task_artifacts.sql`	Task-artifact links
`task_execution_steps.sql`	Per-step execution audit log
`task_messages.sql`	Task message history
`task_push_notification_configs.sql`	Per-task push notification config
`user_contexts.sql`	User conversation contexts
`user_session_analytics.sql`	Session analytics view

Versioned migrations live in schema/migrations/, discovered at build time by the crate's build.rs and returned through the extension_migrations! macro. Schema DDL (schema/*.sql) is for first-install table creation; migrations carry subsequent state transitions.

Key Components

A2A Protocol Server (`services/a2a_server/`)

Implements the Agent-to-Agent protocol specification:

Component	Purpose
`server.rs`	`AgentServer` construction
`standalone.rs`	Entry point for spawned agent subprocesses
`handlers/`	Card, push notification config, and message request handlers
`processing/`	AI execution, conversation/message handling, strategy selection, task building
`streaming/`	SSE event loop, broadcast, webhook client
`auth/`	JWT validation middleware
`errors/`	JSON-RPC error mapping

Agent Orchestration (`services/agent_orchestration/`)

Manages agent subprocess lifecycle:

Component	Purpose
`orchestrator/`	`AgentOrchestrator`: start, stop, restart, status, cleanup
`lifecycle/`	State machine + post-start verification
`monitor.rs`	Health probing via agent cards
`port_manager/`	Dynamic port allocation with reachability probes
`process/`	Subprocess command builder + signal handling
`reconciler.rs`	Reconcile DB state with running processes
`event_bus.rs` / `events.rs`	`AgentEventBus` + `AgentEvent`

Context Management

Conversation context with full history:

Component	Purpose
`repository/context/`	`ContextRepository` (CRUD + message persistence)
`services/context.rs`	`ContextService` (load conversation history for AI)
`services/context_provider.rs`	`ContextProvider` trait impl

Public Exports

pub use models::a2a::{
    A2aJsonRpcRequest, A2aRequestParams, A2aResponse, AgentCapabilities,
    AgentCard, AgentInterface, AgentProvider, AgentSkill, Artifact,
    DataPart, Message, MessageSendParams, Part, SecurityScheme, Task,
    TaskIdParams, TaskQueryParams, TaskState, TaskStatus, TextPart,
    TransportProtocol,
};

pub use error::{
    AgentError, AgentResult, ArtifactError, ContextError,
    ProtocolError, RowParseError, TaskError,
};

pub use services::{
    AgentEvent, AgentEventBus, AgentHandlerState, AgentOrchestrator,
    AgentServer, AgentStatus, ContextService, SkillService,
};

pub use repository::content::ArtifactRepository;
pub use extension::AgentExtension;
pub use state::AgentState;

pub const A2A_PROTOCOL_VERSION: &str = "0.3.0";

Dependencies

Crate	Purpose
`systemprompt-models`	Shared domain types
`systemprompt-traits`	`ContextProvider`, `AgentRegistryProvider`, related traits
`systemprompt-identifiers`	Typed IDs (`TaskId`, `ContextId`, `UserId`, `SessionId`, …)
`systemprompt-extension`	`Extension` trait + registration
`systemprompt-config`	Profile + runtime config
`systemprompt-database`	SQLX pool and helpers
`systemprompt-events`	Event bus + SSE plumbing
`systemprompt-logging`	`tracing` setup helpers
`systemprompt-loader`	Filesystem discovery helpers
`systemprompt-security`	JWT / signing primitives
`rmcp`	MCP protocol client

Features

The crate is feature-flag-free; functionality is unconditional. The facade crate systemprompt gates inclusion via its agent / full features.

License

BSL-1.1 (Business Source License). Source-available for evaluation, testing, and non-production use. Production use requires a commercial license. Each version converts to Apache 2.0 four years after publication. See LICENSE.

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systemprompt-agent 0.13.0