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busbar-plane-a2a

First-party signed kind:plane plugin cdylib: the a2a plane, packaged as a droppable busbar plugin. Drop the signed tarball into plugins/.

kind alias crate busbar license
plane a2a busbar-plane-a2a-plugin 1.6.0 (pinned in .busbar-ref) Apache-2.0

ci

What it is for

busbar-plane-a2a is busbar's kind: plane plugin for the Agent2Agent (A2A) protocol. It fronts the external A2A agents an operator registers: callers reach each agent through busbar on the protocol's three lines (JSON-RPC, HTTP+JSON and gRPC, mounted under /a2a), busbar verifies each agent's card against an operator-supplied trust root, and every hop is governed, metered and audited by the kernel. It also serves busbar's own agent card and A2A push notifications. The plane opens no socket of its own: its hops ride the host's http and grpc needs.

Config

Off by default: a document with no agents: section states no route.

  • agents: (the section the plane declares): one entry per registered agent, by name, plus two reserved section-level keys.
    • agents.<name>.url: the agent's real A2A endpoint (never shown to callers).
    • agents.<name>.pin: the trust root, required: mechanism (unpinned spelled out when none), key, fingerprint.
    • agents.<name>.client_identity: the client certificate busbar presents (cert, key, secret references); required under pin.mechanism: mtls.
    • agents.<name>.reverify_ttl: the longest a card verification is reused (default 5s).
    • agents.<name>.recovery_backoff: how long after a drift a clean answer is disbelieved.
    • agents.<name>.protocol_version: accepted, read by nothing.
    • agents.<name>.allow_private: may the agent live on a private or loopback address (default false).
    • agents.<name>.upstream_credentials: the outbound credential mode (passthrough is refused).
    • agents.<name>.upstream_credential: the leased credential busbar presents on the hop (a secret-store handle and its lease policy).
    • agents.<name>.egress_scopes: judged for shape, read by nothing.
    • agents.<name>.hooks: hooks attached to this agent, added to agents.hooks.
    • agents.hooks, agents.upstream_credentials: the all-agents hooks and credential default.
  • pools: (the top-level failover pools whose members are agents: registrations): handed to the plane under agents:, first member the primary.
  • agent_push: (the plane's own section, read at open and re-judged at every reload): ca, the operator CA (PEM) push callbacks are verified against. Absent = off.

Diagnostics

The codes this plane raises (stated in plane-a2a/declares.json):

code slug severity
BUSBAR-2030 a2a-task-chain-verify-failed actionable
BUSBAR-7003 a2a-pool-not-interchangeable benign_recurring
BUSBAR-7013 a2a-outbound-cred-unleased actionable
BUSBAR-7018 a2a-relayed-stream-refused benign_recurring
BUSBAR-7020 a2a-relayed-outcome-unrecorded actionable
BUSBAR-7021 a2a-relayed-submission-failed benign_recurring
BUSBAR-7023 a2a-failure-unrecorded actionable
BUSBAR-7024 a2a-task-rows-unreadable actionable
BUSBAR-7025 a2a-task-state-unread actionable
BUSBAR-7031 a2a-split-record-unread actionable
BUSBAR-7032 a2a-split-record-stray-parts benign_recurring
BUSBAR-7104 plane-sse-frame-not-utf8 actionable

Build

cargo build --release -p busbar-plane-a2a-plugin

Tests

cargo test --workspace --locked

License

Apache-2.0. See LICENSE.