x-protolabs/effect-domain-v1 is an A2A extension implemented as an after-hook interceptor (src/executor/extensions/effect-domain.ts). It does two things around every skill execution:

1. before — stamps the current skill name onto outbound request metadata as x-effect-domain-skill, so the agent knows which skill is being invoked and can report the deltas it observed.
2. after — reads any worldstate-delta artifact the agent returned in its terminal Task and re-publishes the observed mutations on the world.state.delta bus topic for downstream observability.

There is no planner. This extension is purely a reporting/observability hook: it surfaces agent-reported state mutations onto the bus. The consumer is task-tracker.ts, which de-dupes per task and emits the same world.state.delta events for fleet observability and health.

Extension URI: https://proto-labs.ai/a2a/ext/effect-domain-v1

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Purpose

When an agent applies a change to some shared state (closes a PR, triages an issue), it can report that mutation as a worldstate-delta artifact part on its terminal A2A Task. The effect-domain after-hook lifts those reported deltas onto the bus as world.state.delta events so the dashboard and fleet-health tooling can observe them in near-real-time rather than waiting for the next full poll.

The deltas are observed, agent-reported facts — not predictions consumed by any scheduler or selector.

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Wiring

Call registerEffectDomainExtension(bus) once at startup (in src/index.ts) with a live EventBus. This registers the interceptor with defaultExtensionRegistry. The after hook needs the bus reference to publish world.state.delta.

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worldstate-delta artifact

Agents report mutations via a structured data artifact part on their terminal Task, using MIME type application/vnd.protolabs.worldstate-delta-v1+json (defined in packages/a2a/src/extensions.ts). The discriminator rides on the part's metadata.mimeType; the payload is in content.value. Each entry:

Field	Type	Description
domain	string	Name of the world-state domain (e.g. ci, github_issues)
path	string	Dot-separated path into the domain's data object (e.g. data.blockedPRs)
op	"set" | "inc" | "push"	Mutation operation: replace, add-to, or append
value	unknown	Value to set, increment by, or append (must be a number for inc)

Example artifact data payload:

{
  "deltas": [
    { "domain": "ci", "path": "data.blockedPRs", "op": "inc", "value": -1 },
    { "domain": "board", "path": "data.untriaged", "op": "inc", "value": -1 }
  ]
}

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Published event

After a skill execution whose terminal artifact carried a worldstate-delta part, the interceptor publishes on world.state.delta:

{
  source: string;   // agent that produced the delta
  skill: string;    // skill that was executed
  deltas: WorldStateDeltaEntry[];
}

task-tracker.ts subscribes to the A2A response path, extracts the same delta parts, and emits world.state.delta idempotently per task — the canonical consumer for observability and fleet health.

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Versioning

This is version 1 of the effect-domain extension. The URI https://proto-labs.ai/a2a/ext/effect-domain-v1 is stable. Breaking changes will be published under a new versioned URI.