Python SDK 0.4.0a3

Prepared-template launch now waits for ready_cmd success within its existing readiness budget after process-start acknowledgement. Early nonzero probes are retried; timeouts and cancellation preserve owned cleanup. No new launch parameter or provider capability is added.

The client and server remain a lockstep alpha pair. The repository publication workflow validates this tag, builds/preserves four artifacts, publishes server then client, and verifies public hashes plus a clean official-index installation. Follow the workflow status for PyPI availability.

Verified before tagging: all 13 owner CI checks, real delayed-readiness/deadline/cancellation with independent cleanup, and complete default/portable/proxy OpenSandbox T4 against the exact SDK candidate. This does not certify all templates, models or production workloads.

Fix: #122
Issue remains open until actual public-package replay: #121

Public PyPI verification completed: both 0.4.0a3 projects, four artifacts matched the preserved release candidate and actual downloads, and a fresh official-index client installation with matching automatic server dependency/imports/pip check passed. Install with python -m pip install --index-url https://pypi.org/simple "agent-sandbox-client==0.4.0a3".

Publication run: https://github.com/Alibaba-Agent-Sandbox/python-sdk/actions/runs/40209677091