Waitpoints

A waitpoint is the durable row that represents a paused step on a flow run. The flow run row only carries status (PAUSED, RUNNING, …); the why lives on the waitpoint.

stateDiagram-v2
    [*] --> PENDING: createWaitpoint
    PENDING --> COMPLETED: resume signal
    COMPLETED --> [*]: flow resumes
    [*] --> COMPLETED: pre-completed (resume arrived first)

Schema

Types

• DELAY: resumes at resumeDateTime. The server schedules a one-time job for that timestamp. The delay is bounded by a configurable server-side maximum.
• WEBHOOK: resumes on any HTTP call to the waitpoint's resume URL. If responseToSend is set, it is replied immediately to the original trigger so a single webhook can respond-then-pause.
• BARRIER: resumes once every awaited thing has reported back. See below.

Barriers

A barrier pauses a run until N things report back — the batches a Process in Batches step dispatched, or the approvers on one approval. It is a waitpoint plus one signal row per awaited thing, created up front:

Release is an unconditional floor rule: a sealed barrier releases once no signal is still PENDING. No configuration can produce a hang. policy only ever releases sooner — requiredSuccesses covers 2-of-3 approvals, releaseOnFirstFailure covers a veto. Signals left pending at an early release are reported truthfully as stillRunning.

The step resumes with one shape, so an expression never breaks on fan-out width:

{ "total": 3, "succeeded": 2, "failed": 1, "rejected": 0, "canceled": 0,
  "notDispatched": 0, "stillRunning": 0, "timedOut": false,
  "signals": [ { "sequence": 0, "label": null, "outcome": "SUCCEEDED", "result": null, "runId": "..." } ] }

The signals array is present only when total <= 100; above that only the counts travel and signalsTruncated is set. AP_MAX_BARRIER_SIGNALS (default 10 000) caps how many things one barrier may wait on. A barrier's deadline is set when it is created, from AP_PAUSED_FLOW_TIMEOUT_DAYS, and never moves.

Lifecycle

1. Create. The piece calls ctx.run.createWaitpoint({ type, ... }) + ctx.run.waitForWaitpoint(id). The engine marks the step as paused and asks the server to insert a PENDING row. The insert is idempotent on the (flow run, step) pair.
2. Checkpoint. The engine serializes the execution context and transitions the flow run to PAUSED.
3. Resume signal. Either an HTTP call on the resume URL or the scheduled job firing. Both carry { body, headers, queryParams }.
4. Re-run. A worker rebuilds the context and re-invokes the same action with ctx.executionType === ExecutionType.RESUME and ctx.resumePayload populated.

sequenceDiagram
    participant Piece
    participant Engine
    participant Server
    participant Queue as Job queue
    participant Caller as Resume caller

    Piece->>Engine: createWaitpoint + waitForWaitpoint
    Engine->>Server: register waitpoint
    Server-->>Engine: { id, resumeUrl }
    Engine->>Engine: checkpoint context, status = PAUSED
    Note over Piece,Server: ...time passes...
    Caller->>Server: HTTP call on resumeUrl
    Server->>Queue: enqueue resume job
    Queue->>Engine: resume
    Engine->>Piece: re-invoke with resumePayload

Resume-before-pause race

A callback can arrive before the flow run has finished writing PAUSED to disk. The protocol absorbs the race:

• Completing a waitpoint takes a write lock on the PENDING row. If it exists, it flips to COMPLETED and stores the resumePayload. If it does not, a pre-completed row is inserted instead.
• When the flow run transitions to PAUSED, the server checks for a matching COMPLETED waitpoint and enqueues the resume job immediately.

Duplicate callbacks are absorbed by the uniqueness constraint; the engine never processes a resume twice.

Endpoints

Piece API

Piece authors create waitpoints with ctx.run.createWaitpoint / ctx.run.waitForWaitpoint. Patterns for WEBHOOK, DELAY, and responseToSend are in Flow Control.