IAEMOD-61187: Guard the ESLint warning baseline against regressions

[fpigeonjr]

Description

Adds a ratcheting warning-baseline gate for ESLint, wired into CI alongside the existing ng lint step for both the root workspace and test-app.

• eslint-baseline.json (new) — records the current accepted warning ceiling per workspace, measured from ng lint --format json: root: 1631, test-app: 4. This is the reproducible baseline from the ESLint migration (tslint → ESLint + Angular template a11y gate (ADR-0006) #566) and the warn-first debt tracked in Burn down ESLint and Angular lint debt #580.
• scripts/check-lint-baseline.mjs (new) — reads an ESLint JSON report, sums errorCount/warningCount per workspace, and:
  • Fails if errorCount > 0, regardless of the warning count — errors are never allowed.
  • Fails if warningCount exceeds the recorded baseline for that workspace, printing expected: <= N / actual: M plus a remediation hint.
  • Passes silently if warnings are at or below the baseline.
  • Supports --bump <workspace> <report>, which lowers (never raises) the baseline to the measured warning count, so a cleanup PR can lock in a reduction without hand-editing eslint-baseline.json or CI config.
• scripts/check-lint-baseline.test.mjs (new) — 12 node --test cases covering pass/fail thresholds, error-precedence over warnings, ratchet-only --bump behaviour, and malformed/missing baseline entries.
• package.json / test-app/package.json — add lint:report (JSON-format ng lint run), lint:baseline (report + gate), and lint:baseline:bump scripts to each workspace.
• .github/workflows/lint.yml — adds a "Guard <workspace> ESLint warning baseline" step after each existing ng lint step.
• .gitignore — ignore the generated eslint-report.json / .eslintcache artifacts in both workspaces.

Motivation and Context

#580 (burn down ESLint/Angular lint debt) needs a gate that prevents the accepted warning baseline from regressing while cleanup PRs are still landing incrementally. ng lint's built-in maxWarnings option only supports one fixed number and would need a CI-config edit on every cleanup PR to ratchet down; this script keeps the ratchet in a single committed JSON file instead.

Closes #581

Type of Change (Select One and Apply Label)

• Bug fix (non-breaking change which fixes an issue) → Apply bugfix label
• New feature (non-breaking change which adds functionality) → Apply enhancement label
• Breaking change (fix or feature that would cause existing functionality to change) → Apply breaking label
• Documentation / configuration update → Apply maintenance label

How to Test

1. Root workspace: npm ci && npm run lint:baseline — should print ✓ root: 1631 warnings (baseline 1631), 0 errors. Lint baseline gate passed.
2. test-app: npm ci --prefix test-app && npm --prefix test-app run lint:baseline — should print ✓ test-app: 4 warnings (baseline 4), 0 errors. Lint baseline gate passed.
3. Unit tests: node --test scripts/*.test.mjs — 12 tests should pass.
4. Regression check: temporarily add an any-typed export to any root .ts file, then re-run npm run lint:baseline — it should fail with ✖ root: ESLint warning baseline exceeded and print expected (1631) vs. actual (1632) counts. Revert the temp change.
5. CI: confirm the Lint workflow runs the new "Guard root/test-app ESLint warning baseline" steps after each existing lint step and passes on this branch.

Expected result: Both workspaces' lint baseline gates pass at the current recorded counts; the unit tests all pass; an injected extra warning fails the gate with an actionable message; ESLint errors would fail the gate regardless of warning count (verified via the "fails on errors even when warnings are within baseline" unit test, since no errors currently exist in the repo to reproduce live).

Screenshots (if appropriate)

N/A — CI/configuration change only.

Checklist

• Branch name follows convention (e.g. gh-<number>-<slug>)
• PR title starts with a verb in the imperative mood
• I have self-reviewed my own code
• format:check passes (npm run format:check)
• lint passes (npm run lint)
• build passes (cd test-app && npm run build)
• Tests pass and coverage is reported (cd test-app && npm test)
• If this change requires a documentation update, I have updated it accordingly
• If there are dependent changes, they have been merged and published in downstream modules

[Copilot]

Pull request overview

Adds an ESLint warning-baseline ratchet for the root workspace and test app.

Changes:

• Adds baseline-checking and bump commands with unit tests.
• Records current warning ceilings.
• Integrates baseline checks into CI and ignores generated artifacts.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
.github/workflows/lint.yml	Runs baseline guards in CI.
.gitignore	Ignores generated ESLint artifacts.
eslint-baseline.json	Records workspace warning ceilings.
package.json	Adds root baseline scripts.
test-app/package.json	Adds test-app baseline scripts.
scripts/check-lint-baseline.mjs	Implements checking and ratcheting.
scripts/check-lint-baseline.test.mjs	Tests the baseline CLI behavior.

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