fix(workers): improve startup configuration compatibility

[jromualdez-scale]

Summary

• Reuse the configured AGENT_API_KEY during worker startup registration.
• Preserve existing configuration when the response omits agent_api_key or returns null/empty; keep environment values synchronized when a replacement is returned.
• Keep request configuration consistent across retries and report concise startup errors.

The shared helper serves both FastACP and Temporal workers. No generated client code, provisioning behavior, release configuration, or deployment tooling changes are included.

Validation

• pytest tests/lib -n 0 -q: 1,171 passed, 3 skipped on the current main baseline.
• Coverage includes optional response fields, configured headers, environment updates, retries, diagnostics, and both FastACP and Temporal startup paths.
• Ruff checks pass for all three changed files. Pyright reports zero errors or warnings for those files. git diff --check passes.
• Built the agentex-sdk wheel locally and verified it contains the exact updated registration helper.

Draft pending review and end-to-end verification with rebuilt agent images. No package release or deployment is included.

Confidence Score: 5/5

The PR appears safe to merge based on the reviewed changes.

Summary

Worker registration reuses the configured AGENT_API_KEY, keeps it when the server returns no replacement, and avoids logging request payloads or response bodies.

• Workers register with their configured key and keep it when the server omits one.

_{Reviews (2) · Last reviewed commit: "test(workers): isolate startup configura..." · Reviewed by Greptile}