[xxvw]

Summary

• reject new async operations immediately after close while allowing queued and in-flight work to finish
• close the underlying transport exactly once after the final accepted operation
• preserve caller-owned executors and shut down only the client-owned default executor
• make submit/close races non-blocking and preserve CompletionException identity and cleanup failures
• document the lifecycle contract and add deterministic concurrency tests

Related Issue

Closes #109

Type of Change

• Feature
• Bug fix
• Test
• Documentation
• Refactor
• Build / CI
• Release

Checklist

• I created a branch before making changes.
• I did not commit directly to main.
• I used this pull request template.
• I linked the relevant issue where possible.
• I added or updated tests.
• I updated documentation if needed.
• Unreleased notes are consolidated in feat: improve environment-based client setup #113 to avoid cross-PR conflicts.
• I ran mvn clean verify.
• I did not include names of automated development tools in project artifacts.
• I did not expose API tokens, secrets, private keys, account IDs, database IDs, customer data, or sensitive data.
• I did not add new runtime dependencies without an issue and maintainer approval.

Testing

mvn -B clean verify javadoc:javadoc

All 113 tests passed, including deterministic queued, in-flight, acceptance-race, executor-rejection, post-close, cleanup-failure, and exception-identity cases.

Notes

close() remains non-blocking for accepted work. Deferred transport cleanup failures are surfaced through the final accepted future. Merge #113 after this pull request to add the consolidated changelog entry.