Enforce Checkstyle in CI: failsOnError/failOnViolation are disabled

[devops-thiago]

Background

Checkstyle is configured in pom.xml with failsOnError=false and failOnViolation=false, and the CI job runs mvn checkstyle:check with continue-on-error: true (.github/workflows/ci.yml). The Checkstyle step can therefore never fail the build or the pipeline — the check is decorative.

Impact

• Code style violations are never surfaced to developers or blocked at merge time.
• The README advertises Checkstyle as part of the "automated code quality" story, which is misleading.
• Style drift accumulates over time; Spotless only enforces formatting, not style rules.

How to reproduce

1. Introduce a Checkstyle violation (e.g. a line exceeding the configured limit or a missing Javadoc where required).
2. Run mvn checkstyle:check — violations are reported but the build exits 0.
3. Push to a branch — the code-quality CI job reports Checkstyle failures with continue-on-error and still passes.

Where the fix should land

Decide on an enforcement policy, then:

• Set failsOnError=true and failOnViolation=true in pom.xml and fix the violations that surface.
• Remove continue-on-error: true from the Checkstyle step in .github/workflows/ci.yml.
• Consider adding a checked-in checkstyle.xml (currently none exists; the plugin falls back to google_checks.xml) if stricter rules are desired.

Files touched

• pom.xml
• .github/workflows/ci.yml
• checkstyle.xml (new, optional)

Acceptance criteria

• mvn checkstyle:check exits non-zero on a deliberately introduced violation.
• CI code-quality job fails when Checkstyle reports violations.
• The existing codebase passes the enforced rules (no build regressions).
• mvn test is green.