test: Add unit tests for error handling utilities

[google-labs-jules]

This commit adds a new test file, core/util/errors.test.ts, to provide test coverage for the getRootCause function and the ContinueError class. The tests cover various scenarios, including nested errors and constructor behavior.

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PR created automatically by Jules for task 5059259321375601378 started by @Patrick-Erichsen

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Summary by cubic

Added unit tests for getRootCause and ContinueError to validate root cause resolution and constructor behavior. Covers nested and deeply nested errors; checks reason, name, and default empty message.

^{Written for commit 38f7788. Summary will update automatically on new commits.}

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[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

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I have read the CLA Document and I hereby sign the CLA

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_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}

[continue]

✅ Fixed prettier formatting issues in core/util/errors.test.ts. The CI checks should now pass.

[continue]

⚠️ CLA Check Status

The CLA (Contributor License Agreement) check is failing because this PR was created by a bot (google-labs-jules[bot]) and my formatting fix commit was made by continue[bot].

To resolve this:

• A human contributor (likely @Patrick-Erichsen, who started the original task) needs to comment on this PR with:

  I have read the CLA Document and I hereby sign the CLA
  

This will satisfy the CLA requirement and allow the PR to be merged.

Note: As an automated agent, I cannot sign the CLA on behalf of human contributors. The prettier formatting issue has been fixed, but the CLA signature requires human action.

[continue]

CI Test Failures - Not Related to This PR

The failing tests are unrelated to the changes in this PR:

Failed Tests:

• hubLoader.test.ts > Real Hub Integration Tests - HTTP 502/504 Gateway errors

These are flaky integration tests that depend on external Hub services being available. The failures are due to the Hub service returning gateway timeout errors (502/504), not code issues.

This PR's Changes:

• Added unit tests in core/util/errors.test.ts
• Applied prettier formatting
• Did not modify any CLI code or Hub loader functionality

What's Happening:

The cli-pr-checks.yml workflow tests the CLI extension, but this PR only adds tests to the core module. The failing tests existed before this PR and are experiencing temporary infrastructure issues with external services.

Recommendation:

These tests should either:

1. Be retried (they're flaky)
2. Be marked as non-blocking for external service failures
3. Use mocked responses instead of real HTTP calls

The code changes in this PR are valid and properly formatted.