refactor: replace deprecated tseslint.config with defineConfig

[Wintus]

Summary

• Replace deprecated tseslint.config() with ESLint's native defineConfig() from eslint/config

Background

The tseslint.config() function was deprecated in favor of ESLint's defineConfig() (introduced in ESLint v9.22.0).

Reference: https://typescript-eslint.io/packages/typescript-eslint/#config-deprecated

Test plan

• npm run lint passes
• npm run build passes

Co-Authored-By: Claude

[claude]

Code Review

Summary

This PR refactors the ESLint configuration to use the recommended defineConfig() from ESLint instead of the deprecated tseslint.config(). The change is minimal, focused, and follows best practices.

✅ Positive Observations

1. Addresses Deprecation: The PR correctly migrates from the deprecated tseslint.config() to the recommended defineConfig() approach.

2. Minimal Surface Area: The change is surgical - only modifying what's necessary (1 import + 1 function call).

3. Test Coverage: All CI checks pass:

   • ✓ Lint passes
   • ✓ Tests pass
   • ✓ Type check passes

4. Clear Documentation: The PR description provides context with a reference link to the deprecation notice.

5. Proper Co-Authoring: Attribution to Claude is included in the commit message.

🔍 Technical Analysis

Code Quality: ★★★★★

• Clean, straightforward refactoring
• No unnecessary changes
• Maintains existing configuration structure

Compatibility:

• ESLint v9.39.2 is used (the change requires v9.22.0+) ✓
• The defineConfig import from eslint/config is the correct approach

Functional Equivalence:
The migration maintains identical behavior since defineConfig() serves the same purpose as the deprecated tseslint.config() - both provide type safety for ESLint flat configs.

⚠️ Potential Consideration

Minor: While this change is correct, I'd note that the PR description mentions this was deprecated in favor of ESLint's native function. However, it's worth noting that tseslint.config() was a TypeScript-ESLint utility, and ESLint's defineConfig() is now the recommended standard for flat configs. The existing code still uses tseslint.configs.recommended which is appropriate and not deprecated.

🎯 Verdict

LGTM ✓ This is a clean, necessary refactoring that properly addresses the deprecation. No issues found.

Risk Level: Low
Impact: Maintenance (reduces deprecation warnings)
Recommendation: Approve and merge

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Review generated following the project's functional programming style guide and TDD workflow as outlined in CLAUDE.md