Agent Stream Protocol

a13n-stream-protocol observes public a13n-harness streams as typed AG-UI 1.0 events. It maps text, reasoning, tool, and terminal observations to standard AG-UI events, exposes every other public observation through a namespaced CUSTOM fallback, applies an optional Host processor, and accumulates the resulting events for process-local use.

The repository directory is packages/a13n-stream-protocol, the Python distribution is a13n-stream-protocol, and the import package is a13n_stream_protocol.

Usage

from a13n_stream_protocol import HarnessAguiStreamObserver

observer = HarnessAguiStreamObserver()
async with executable.stream(input, bindings=bindings) as stream:
    async for item in stream:
        new_events = observer.observe(item)
        await host.persist_and_publish(new_events)

One stream observer binds to the root Thread and Run on its first successful source item. Forwarded inline children have independent state and carry subagentRunId, preserving native message and tool-call IDs. Independently executed asynchronous children use separate stream observers. HarnessAguiObserver remains available for sources containing exactly one Run.

A Host that retains the exact public Harness source history can atomically rebuild a fresh observer before continuing with live items:

observer = HarnessAguiStreamObserver()
await observer.resume(host.source_history(run_id=run_id, through=cursor))

async for item in host.live_source(run_id=run_id, after=cursor):
    new_events = observer.observe(item)
    await host.persist_and_publish(new_events)

The history is a finite async iterable for one root stream, including its inline child observations. resume() accumulates its post-processor AG-UI events without returning them for duplicate publication, leaves the observer fresh if reconstruction fails, and knows nothing about storage, cursors, gaps, or replay-to-live cutover. Those remain Host responsibilities.

A Host can filter or adjust converted values before accumulation:

from ag_ui.core import Event
from ag_ui.core.events import CustomEvent
from a13n_harness import HarnessStreamEvent
from a13n_stream_protocol import HarnessAguiObserver


def process_event(
    source: HarnessStreamEvent[object],
    event: Event,
) -> Event | None:
    del source
    if isinstance(event, CustomEvent) and event.name == "a13n.harness.diagnostic":
        return None
    return event


observer = HarnessAguiObserver(processor=process_event)

A replacement must retain the same AG-UI event type and source-derived correlation. The processor is synchronous, replay-stable, and does not retain mutable processing state or persist, publish, or acknowledge events. The Host acts on the complete batch returned by live observe() calls.

Ownership

The package owns only:

standard Harness-to-AG-UI conversion;
generic CUSTOM fallback for unmapped public events;
multipart text, reasoning, and tool-call observation state;
optional replay-stable Host processing;
atomic process-local reconstruction from supplied source history;
detached incremental results and accumulated snapshots.

The Host owns source-history retention and selection, cursors, gaps, replay-to-live cutover, persistence, event identities, fan-out, backpressure, cancellation, transport, and rendering policy. The Harness owns source lifecycle facts and continuation state.

Dependencies

The source manifest declares an unversioned dependency on a13n-harness, so uv resolves Harness from the workspace during repository development. Conversion uses the upstream ag-ui-protocol models, Pydantic serialization, and the lightweight pydantic-ai-slim event runtime. The package does not depend on Harness UI, a Host persistence model, or a transport framework.

Release automation replaces the workspace-oriented Harness dependency in publishable metadata with an exact same-version requirement. Both the sdist and wheel therefore install only the Harness version released with that Stream Protocol artifact.

Versioning

Agent Stream Protocol and a13n-harness form the Harness release group. A release/a13n-harness-v<version> tag publishes both distributions at exactly the same version, where <version> is stable X.Y.Z or RC X.Y.Z-rc.N. Python package metadata represents the RC as X.Y.ZrcN. This package pins the exact Harness version. Harness UI is versioned and released independently.

The accepted architecture and observation contract are defined in the Agent Stream Protocol specification.

Metadata

Release files for a13n-stream-protocol 0.5.1

For a detailed explanation of source distributions (sdists) and built distributions (wheels), please see the package formats documentation.

Source distribution (sdist)

Source distribution for a13n-stream-protocol 0.5.1
File	Size	Uploaded
a13n_stream_protocol-0.5.1.tar.gz	47.2 kB	Oct 1, 2026	Details

Built distribution (wheel)

Table of built distributions (wheels) for a13n-stream-protocol 0.5.1
File	Interpreter	ABI	Platform	Reset
a13n_stream_protocol-0.5.1-py3-none-any.whl 18.9 kB Oct 1, 2026	Python 3	none	any	Details

Total release size: 66.1 kB

Release files / a13n_stream_protocol-0.5.1.tar.gz

Download URL	a13n_stream_protocol-0.5.1.tar.gz
Size	47.2 kB
Tags	Source
SHA-256 checksum How to use checksums	`81f123c6b434735a49aee6eb7d6ff50040c20d987b3ae5354c2adf673ca9e710`
BLAKE2b-256 checksum How to use checksums	`d9065dd0502c9c5c6882a8bde41a299c97c8f0508c79c4b13707066962e8c1d2`
Upload date	Oct 1, 2026
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`uv/0.12.21 {"installer":{"name":"uv","version":"0.12.21","subcommand":["publish"]},"python":null,"implementation":{"name":null,"version":null},"distro":{"name":"Ubuntu","version":"24.04","id":"noble","libc":null},"system":{"name":null,"release":null},"cpu":null,"openssl_version":null,"setuptools_version":null,"rustc_version":null,"ci":true}`

Release files / a13n_stream_protocol-0.5.1-py3-none-any.whl

Download URL	a13n_stream_protocol-0.5.1-py3-none-any.whl
Size	18.9 kB
Tags	Python 3
SHA-256 checksum How to use checksums	`50f3be5e044de710ec02ff40d553b55ead75de3b7f17a3170691aa81cc33897e`
BLAKE2b-256 checksum How to use checksums	`870968a267c183cf75ed5caefcc0ff702633fd8466aef0e16777318f5d3c510d`
Upload date	Oct 1, 2026
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`uv/0.12.21 {"installer":{"name":"uv","version":"0.12.21","subcommand":["publish"]},"python":null,"implementation":{"name":null,"version":null},"distro":{"name":"Ubuntu","version":"24.04","id":"noble","libc":null},"system":{"name":null,"release":null},"cpu":null,"openssl_version":null,"setuptools_version":null,"rustc_version":null,"ci":true}`