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ADR 0008: Standalone A2A Transport Module（英文规范）

  • Status: Accepted for Spec 029 implementation
  • Date: 2026-07-30
  • Decision owners: A2A Router and Platform Architecture

Context

NeKiro's Router currently contains a private package that combines reusable HTTP/JSON-RPC/SSE client mechanics with NeKiro-specific target resolution, signed credentials, platform context, active Profile mapping, Platform Error codes, result events, cancellation policy, and Ledger orchestration.

The platform already depends on the protocol-focused github.com/a2aproject/a2a-go v0.3.15. Reimplementing the complete A2A protocol would contradict ADR 0001. Keeping all hardening private, however, prevents independent reuse and couples its release cadence to the entire platform.

Decision

  • github.com/NeKiro-project/nekiro-a2a-transport-go becomes the standalone upstream for reusable A2A HTTP/JSON-RPC/SSE client mechanics.
  • The module depends only on Go standard packages and the A2A protocol library pinned by its declared compatibility identity.
  • Public calls require an explicit endpoint and explicit positive byte bounds. Caller metadata is supplied only through explicit interceptors.
  • The module rejects redirects, malformed or mismatched JSON-RPC envelopes, invalid media/framing, duplicate SSE IDs/members, trailing data, unsupported event kinds, and responses/events above explicit limits.
  • Streaming returns official decoded events and immutable raw result bytes so callers do not need to reserialize Agent data.
  • Transport failures use a transport-only typed taxonomy. NeKiro maps them to Platform Error v4 in its Router adapter.
  • NeKiro contracts remain the source of truth for A2A Profile, Task-state and Message validation, context headers, credential claims, public errors, and result events.
  • NeKiro retains routing, exact resolution, Card limits, credentials, cancellation policy, platform event mapping, Ledger writes, and terminal races.
  • Upstream releases use immutable semantic-version tags. NeKiro production manifests must not contain a local replacement or a fallback copy.

Consequences

  • External Go consumers can reuse the hardened transport without importing the NeKiro platform.
  • NeKiro gains a second repository and explicit upstream-before-downstream release ordering.
  • Transport API changes require upstream compatibility review and downstream conformance verification.
  • The language-neutral A2A Profile remains in one authoritative location, so upstream tests must test transport mechanics without redefining platform Task/permission/Ledger semantics.
  • Source provenance and Apache-2.0 attribution are preserved.

Rejected Alternatives

Move the complete Router upstream

Rejected because routing, resolution, authorization, credentials, result mapping, and Ledger behavior are platform responsibilities.

Make upstream import NeKiro contracts

Rejected because it reverses the dependency direction and prevents standalone use.

Fork or replace the official A2A library

Rejected because the existing Profile already selects a protocol-focused upstream and the reusable value here is strict transport policy around it.

Keep a private implementation as fallback

Rejected because dual production paths can drift and hide dependency or compatibility failures.

Fallback Delta

Fallback delta: removed 0, retained 2, added 0, net 0.

Retained policies are Go's documented nil http.Transport behavior and ADR 0006's one bounded remote cancellation propagation attempt. Added fallback evidence: none.