chore(deps): babel coverage, devDeps cleanup, eslint 10 flat config

[JasonSooter]

Before this PR

• jest.config.js used coverageProvider: 'v8' with no collectCoverageFrom and no threshold. v8 collapsed the optional-chaining export guard in src/index.js, reporting a false 100% while a branch was actually uncovered.
• ESLint pinned to 8.57.1 (legacy .eslintrc.js, EOL, carrying transitive advisories), eslint-plugin-jest 27, lint-staged 16.
• devDeps carried unused packages: eslint-config-prettier, eslint-plugin-prettier, eslint-formatter-table, prettier-eslint, node-fetch, semver. lodash was only present transitively (via prettier-eslint). setup.js injected unused crypto/cache globals; .eslintrc.js declared unused jsonwebtoken global.
• wallaby.js duplicated the setup.js globals/coverage config by hand, free to drift from the Jest config.

After this PR

• coverageProvider: 'babel' (honest branch coverage + Wallaby parity), collectCoverageFrom: ['src/**/*.js'], enforced 100% threshold. Added 1 test (module-exports guard, re-require with NODE_DEV unset) to close the newly-visible branch. Coverage 100% all metrics; 2 tests pass.
• ESLint upgraded to ^10.6.0 with a flat eslint.config.js (node-only globals), eslint-plugin-jest ^29.15.4, added @eslint/js ^10.0.1 + globals ^17.7.0. Newly-enforced rules disabled to preserve prior behavior so npx eslint . passes with zero source changes. lint-staged bumped to ^17.0.8.
• Unused devDeps removed; lodash pinned direct at 4.18.1 (Segment runtime global). moment-timezone ^0.5.31 left pinned. jest-fetch-mock kept.
• wallaby.js reduced to autoDetect: ['jest'] (single source of truth = Jest config).
• Lockfile hard-refreshed via Twilio Artifactory; npm audit 0 vulnerabilities.

Reason that prompted this change

• This is the template the JPMC function fleet copies from, so it must carry the canonical babel-coverage + eslint-10-flat-config + cleaned-devDeps baseline. v8 coverage was masking an untested branch, and eslint 8 is EOL.

Test Plan

• npx jest -> 100% statements/branches/functions/lines, 2 tests pass.
• npx eslint . -> exit 0, zero code changes (no --fix churn).
• npm audit -> 0 vulnerabilities.
• Lockfile: all resolved hosts are npmjs.artifacts.twilio.com.
• Pre-commit hook (lint-staged + npm test) exercised by the commit itself and passed.
• No product code (src/index.js) modified; coverage closed via tests only.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Note

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Updates the repo’s dev tooling baseline to use Babel/Istanbul coverage, ESLint 10 flat config, and a simplified Wallaby setup, while cleaning up devDependencies and tightening coverage enforcement.

Changes:

• Switched Jest coverage to Babel with scoped collection + 100% global thresholds; added a test to cover the module export guard branch.
• Migrated from legacy .eslintrc.js to ESLint 10 flat config with updated plugins/globals.
• Simplified wallaby.js to auto-detect Jest and removed duplicated config.

Reviewed changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
wallaby.js	Removes manual Wallaby config and relies on Jest auto-detection to prevent drift.
src/index.test.js	Adds a Jest test to cover the module export guard behavior.
setup.js	Removes unused globals and introduces a RetryError global for tests/lint parity.
package.json	Updates linting toolchain deps and removes unused devDependencies; adds direct lodash pin.
jest.config.js	Switches to Babel coverage provider, scopes coverage collection, and enforces 100% thresholds.
eslint.config.js	Introduces ESLint 10 flat config with node globals + Jest-only overrides for tests.
.eslintrc.js	Removes legacy ESLint configuration.