[codex] fix unit test coverage reporting

[JasonW404]

Summary

Fix the parallel unit-test runner so CI coverage reporting matches the pre-parallel behavior while preserving file-level parallel execution.

Root Cause

PR #3285 changed unit tests from serial --cov-append into per-file coverage data files followed by coverage combine. The new flow only checked that coverage.xml existed and did not fully restore the previous coverage API reporting behavior. The combine/xml phase also needed to consistently use test/.coveragerc without relying on an unsupported --rcfile placement for the installed coverage version.

Changes

• Pass COVERAGE_RCFILE to coverage combine/xml so both phases use test/.coveragerc.
• Restore COVERAGE_PROCESS_START in per-file pytest subprocesses.
• Restore coverage API report validation after combine.
• Restore HTML coverage output under test/coverage_html.
• Restore unit-test summary output: total, passed, failed, pass rate.
• Restore detailed failed test-file reporting.

Validation

• python3 -m py_compile test/run_all_test.py
• git diff --check
• Full local CI setup matching workflow:
  • uv sync --extra data-process --extra test
  • uv pip install -e "../sdk[dev]"
• Full local UT run completed before the coverage combine fix and produced all .coverage.* files.
• Re-ran coverage combine/report against those files successfully: generated test/coverage.xml, emitted coverage report, total coverage about 78.8%.
• Smoke test:
  • NEXENT_PYTEST_TARGETS='test/sdk/core/models/test_prompt_cache.py' NEXENT_PYTEST_WORKERS=1 NEXENT_PYTEST_FILE_TIMEOUT=120 backend/.venv/bin/python test/run_all_test.py
  • Passed and generated test/coverage.xml plus test/coverage_html/.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.