fix: Test suite ESM/TextDecoder compatibility issue blocking all PRs

[ashleyshaw]

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file_type: "issue"
issue_type: "bug"
area: "tests"
priority: "critical"
component: "ci"
status: "needs-triage"

Build/CI Summary

Jest test suite fails with TextDecoder is not defined errors when running tests with ESM modules. This is a pre-existing infrastructure issue blocking all PRs regardless of code quality.

Problem Statement

The test runner does not properly polyfill TextDecoder in ESM mode, causing fixture validation and other tests to fail before checking code quality.

Impact:

• All PRs blocked from merging
• CI/CD pipeline non-functional
• Prevents validation of any code changes

Example Error:

ReferenceError: TextDecoder is not defined
  at Module.<anonymous> (node_modules/@actions/core/...)

Steps / Checklist

• Investigate Jest ESM configuration
• Test different polyfill approaches
• Verify @actions/core compatibility with ESM
• Configure Jest to polyfill TextDecoder in ESM mode
• Run full test suite to verify fix
• Test on multiple Node versions (18+, 20+)
• Update CI configuration if needed
• Document solution in troubleshooting guide

Acceptance Criteria

• Test suite runs without TextDecoder errors
• All existing tests pass without modification
• No changes needed to individual test files
• PR testing works for all code changes
• CI workflow completes successfully
• Documentation updated if configuration changed

Additional Context

Affected Workflows:

• Testing workflow (blocks all PRs)
• All dependent CI checks

Related Issues:

• PR feat: Phase 2 - Planner Agent GitHub API Integration #634 (planner agent enhancements) blocked by this
• Issues fix: Planner agent schema validation infrastructure failure #643, fix: Fixture validation test infrastructure failure blocking all PRs #644 (other infrastructure failures)

Environment:

• Node.js: 20+ (see .nvmrc)
• Package Manager: npm 10+
• Jest Version: (check package.json)
• @actions/core Version: (check package.json)

References

• Jest ESM Documentation
• Node.js Built-ins Polyfill Guide
• TextDecoder API
• CONTRIBUTING.md
• Coding Standards

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Definition of Ready (DoR)

• Build/CI goal and scope defined
• Checklist prepared
• Estimate added

Definition of Done (DoD)

• All checklist and acceptance criteria completed
• Documentation/changelog updated
• Approved by maintainer
• CI workflow stable after fix

[linear-code]

LS-820

[ashleyshaw]

Fixed in PR #675 (commit 141252f).

Changes:

• Re-enabled setupFilesAfterEnv in Jest configuration
• Added independent TextDecoder/TextEncoder polyfills to tests/jest.setup.localstorage.js
• Improved robustness of polyfill checks and planner agent footer replacement

The test suite ESM module compatibility issue with TextDecoder is now resolved.

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