Webhook resume flows and stronger delivery semantics

[stationeros]

Status

v0.3.0 ships signed callback delivery with retry and dead-letter behavior for async jobs.

Remaining problem

Callbacks notify callers when work completes, but the control plane still lacks a first-class workflow resume contract and stronger delivery guarantees for multi-node deployments.

Goal

Add resumable workflow hooks and harden callback delivery semantics.

Scope

• workflow resume endpoint contract
• callback dedupe and idempotent resume handling
• delivery worker lease semantics for multi-replica deployment
• callback replay tooling for operators

Acceptance criteria

• callers can resume a workflow from a callback event without bespoke glue code
• callback events are safe to replay
• delivery state is robust under restart and multi-replica execution