Wire Build stacks to Codecov (Phase 1: tokenless)

[Yicong-Huang]

Task Summary

Wire each Build stack (frontend, scala, python, agent-service) up to Codecov so every PR and main push shows a coverage report and a diff against the main baseline. Phase 1 is tokenless: report uploads only, no PR comments / status check / quality gates yet.

Per-stack coverage generation

stack	tool	command	output
scala	sbt-scoverage (sbt plugin, native to scala)	sbt coverage test coverageReport	**/target/scala-2.13/scoverage-report/scoverage.xml
python	pytest-cov	pytest --cov=. --cov-report=xml -sv	coverage.xml (Cobertura format)
frontend	Karma + Istanbul (Angular's --code-coverage)	nx test --code-coverage	frontend/coverage/<project>/lcov.info
agent-service	bun test --coverage --coverage-reporter=lcov	(built-in)	agent-service/coverage/lcov.info

Codecov upload

codecov/codecov-action pinned to a specific SHA per ASF GitHub Actions Policy, one upload step per stack with a distinct flags: so the dashboard shows each language separately:

- uses: codecov/codecov-action@75cd11691c0faa626561e295848008c8a7dddffe  # v5.5.4
  with:
    files: ./**/scoverage-report/scoverage.xml
    flags: scala
    fail_ci_if_error: false

Tokenless upload: CODECOV_TOKEN not required for public Apache repos in v5; rate-limit fallback channel is enough for Phase 1. Phase 2 (separate task) opens an INFRA ticket to add the token, which unlocks PR comments / commit status / quality-gate enforcement.

Where the steps live

The Build workflow (build.yml) already triggers on:

• push: branches: [main, ci-enable/**, release/**] — uploaded reports become the Codecov baseline
• pull_request: — Codecov compares against the baseline and renders a diff

So adding the coverage generation + upload steps inside each stack's job covers both flows in one change. Skipped stacks (per LABEL_STACKS from #4640) automatically skip their coverage upload.

Out of scope (deferred to Phase 2)

• INFRA ticket for CODECOV_TOKEN
• PR comment / commit status / quality-gate (codecov.yml) configuration
• Onboarding to SonarCloud (orthogonal alternative)

Priority

P2 – Medium

Task Type

• Code Implementation
• DevOps / Deployment