systemprompt-events

Every A2A, AG-UI, analytics, and context event fans out through one bus, and a durable Postgres outbox carries it across replicas so nothing is lost to a restart. Any component holding a UserId can publish without touching the wire format.

Layer: Infra. Infrastructure primitives consumed by the domain and application crates. Part of the systemprompt-core workspace.

What it does

The in-process event bus fans typed events out to per-user SSE connections, managing connection lifecycles and cleaning up disconnected clients. It is not SSE-only: a durable Postgres outbox (event_outbox table, via LISTEN/NOTIFY) relays events across replicas so a multi-instance deployment stays consistent. The crate is shared between the HTTP API entry crate and the runtime layer.

Modules

Module	Purpose
`services`	The `GenericBroadcaster` implementation and per-event aliases, the static `EventRouter`, `ConnectionGuard`, keep-alive utilities, the `PostgresEventBridge` (LISTEN/NOTIFY relay), and the outbox repository.
`sse`	The `ToSse` trait and `serde`-driven impls converting `systemprompt-models` event types into `axum` SSE records.
`extension`	`EventsExtension` declares the `event_outbox` schema through the workspace extension framework.
`error`	`EventError` / `EventResult`.

Schema DDL lives in schema/ (event_outbox.sql plus the migrations/ directory).

Event flow

                    ┌─────────────────┐
                    │   EventRouter   │
                    └────────┬────────┘
                             │
        ┌────────────────────┼────────────────────┐
        │                    │                    │
        ▼                    ▼                    ▼
┌───────────────┐    ┌───────────────┐    ┌───────────────────┐
│AGUI_BROADCASTER│    │A2A_BROADCASTER│    │CONTEXT_BROADCASTER│
└───────┬───────┘    └───────┬───────┘    └─────────┬─────────┘
        │                    │                      │
        ▼                    ▼                      ▼
   SSE Clients          SSE Clients            SSE Clients

AG-UI and A2A events route to both their primary broadcaster and the context broadcaster for aggregation. Across replicas, PostgresEventBridge relays outbox rows so an instance publishes locally and every other instance sees it.

Usage

[dependencies]
systemprompt-events = "0.21"

use systemprompt_events::{AGUI_BROADCASTER, Broadcaster};
use systemprompt_identifiers::UserId;

async fn active_listeners(user_id: &UserId) -> usize {
    AGUI_BROADCASTER.connection_count(user_id).await
}

Public API

Traits

Trait	Methods	Purpose
`Broadcaster`	`register`, `unregister`, `broadcast`, `connection_count`, `total_connections`	Type-safe event broadcasting

Types

Type	Description
`EventSender`	`tokio::sync::mpsc::Sender<Result<Event, Infallible>>`
`EventError` / `EventResult<T>`	`thiserror`-derived error and result alias
`GenericBroadcaster<E>`	Generic broadcaster for any `ToSse + Clone + Send + Sync` event
`AgUiBroadcaster`	`GenericBroadcaster<AgUiEvent>`
`A2ABroadcaster`	`GenericBroadcaster<A2AEvent>`
`ContextBroadcaster`	`GenericBroadcaster<ContextEvent>`
`AnalyticsBroadcaster`	`GenericBroadcaster<AnalyticsEvent>`
`ConnectionGuard<E>`	RAII guard for automatic unregistration
`EventRouter`	Routes events to appropriate broadcasters
`PostgresEventBridge`	LISTEN/NOTIFY relay draining the `event_outbox` table across replicas
`OutboxChannel` / `OUTBOX_CHANNEL`	Outbox notification channel type and name
`EventsExtension`	Extension registering the `event_outbox` schema

Constants

Constant	Value	Purpose
`HEARTBEAT_INTERVAL`	15 seconds	SSE keep-alive interval
`HEARTBEAT_JSON`	`{"type":"heartbeat"}`	Keep-alive payload

Global Singletons

Static	Type	Purpose
`AGUI_BROADCASTER`	`LazyLock<AgUiBroadcaster>`	AG-UI event broadcasts
`A2A_BROADCASTER`	`LazyLock<A2ABroadcaster>`	Agent-to-agent events
`CONTEXT_BROADCASTER`	`LazyLock<ContextBroadcaster>`	Aggregated context events
`ANALYTICS_BROADCASTER`	`LazyLock<AnalyticsBroadcaster>`	Analytics event tracking

Tests

Tests are located in crates/tests/unit/infra/events/ following the project convention of separating tests from source files.

Dependencies

Crate	Purpose
`systemprompt-models`	Event types (`AgUiEvent`, `A2AEvent`, `ContextEvent`, `SystemEvent`, `AnalyticsEvent`)
`systemprompt-identifiers`	`UserId` / `ConnectionId` types (`sqlx` feature)
`systemprompt-extension`	Schema registration for the `event_outbox` table
`tokio`	Async runtime, channels, synchronization
`axum`	SSE `Event` and `KeepAlive` types
`sqlx`	Durable outbox relay over Postgres LISTEN/NOTIFY
`chrono`	Outbox row timestamps
`inventory`	Compile-time extension registration
`serde` / `serde_json`	Event serialization
`tracing`	Structured logging

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-events 0.21.1

Production infrastructure for AI agents