Claude API webhooks eliminate three agent polling loops

Anthropic extended webhooks to cover environment and memory-store lifecycle events on July 22, per the release notes. That cuts three separate polling loops out of the Claude agent API.

Four new environment.* event types and three memory_store.* event types push state changes directly, instead of making you poll for them. That closes the delay between an environment or memory-store change and your code finding out.

The same release adds effort inside the model object at agent creation. It also adds event_deltas[] on the per-thread stream endpoint. That lets you watch a single subagent's text generate instead of waiting on the whole thread to finish.

The bigger change is at session start. POST /v1/sessions now accepts an initial_events array of up to 50 events, and a non-empty array starts the agent loop in that same request. Before July 22, that took two separate calls.

The tell an integration is behind: an SDK wrapper still exposing a manual poll helper for environment or memory-store status. The webhook now pushes that instead.