coordination · beta · free

Barrier Bell

Atomically records opaque participant arrivals against a fixed threshold and TTL. Repeated arrivals by the same participant are idempotent, and the barrier stays released until it expires.

Use when

A workflow phase should release after enough unique agents arrive.
The synchronization point can safely expire after a bounded interval.

Do not use when

Every named participant must arrive or participant identities must be listed.
The barrier must remain durable indefinitely.

Invocation contract

HTTP: /v1/tools/barrier-bell
Version: 0.1.0
Mode: atomic
Idempotency: required
Retention: Only hashes of the namespace, key, and participants remain in Valkey until the barrier TTL expires. The service never lists participants.
Tested with: HTTP/1.1, HTTP/2, MCP Streamable HTTP

Positive and negative examples

{
  "input": {
    "action": "arrive",
    "namespace": "pipeline:example.invalid",
    "key": "phase-rendered",
    "participant": "agent-a",
    "threshold": 3,
    "ttl_seconds": 60
  },
  "output": {
    "action": "arrive",
    "barrier_hash": "sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
    "exists": true,
    "configuration_matches": true,
    "newly_arrived": true,
    "threshold": 3,
    "participant_count": 1,
    "released": false,
    "expires_at": "2026-07-24T12:01:00.000Z"
  },
  "negative": [
    {
      "scenario": "Every named participant must arrive or participant identities must be listed.",
      "expected_error": "INVALID_INPUT",
      "charged": false
    }
  ]
}

Deterministic errors

Code	Retry	Charged	Recovery
INVALID_INPUT	false	false	Correct the request to match input_schema.
TOOL_PAUSED	true	false	Wait for the operator to resume the tool.
RATE_LIMITED	true	false	Retry after the response Retry-After interval.
DEPENDENCY_UNAVAILABLE	true	false	Retry with the same idempotency identity.

Full machine manifest

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