test: add unit tests for API utils and skill prerequisites (Phase 2)

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Summary

Phase 2 of the Daily Test Coverage Improver plan from #55. Adds 54 new unit tests across 3 previously uncovered files.

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Files Added

src/lib/api/validation-utils.test.ts — 24 tests

Pure function tests for validateObject and validateRequiredString:

• Null/undefined/falsy rejections
• Whitespace-only string rejection
• Non-object type rejections (string, number, boolean)
• Documents array behavior (typeof [] === 'object', passes as valid)
• Correct fieldName used in error messages

src/lib/api/response-utils.test.ts — 14 tests

Tests for apiSuccess, validationErrorResponse, serviceUnavailableResponse:

• Correct HTTP status codes (200, 400, 503)
• success: true/false field
• Meta included when provided, omitted when not
• Various data shapes (object, array, null)

src/lib/skills/prerequisites.test.ts — 16 tests

Tests for getNextAchievableSkills:

• Empty profile → only foundation skills returned
• Beginner skills still included (not yet excluded)
• Intermediate/advanced skills excluded from results
• Single prerequisite unlocking (javascript → typescript)
• Multi-prerequisite unlocking (javascript + html + css → react)
• Cascading prerequisites (react + typescript → nextjs)
• Duplicate skill entries → highest level wins
• Two-prereq skill (git + testing → ci-cd)

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Coverage Improvement

File	Before	After
src/lib/api/validation-utils.ts	0%	~100%
src/lib/api/response-utils.ts	0%	~100%
src/lib/skills/prerequisites.ts	0%	~100%

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Test Results

All 54 new tests pass ✅. Full test suite unaffected.

Generated by Daily Test Coverage Improver

To install this workflow, run gh aw add githubnext/agentics/workflows/daily-test-improver.md@828ac109efb43990f59475cbfce90ede5546586c. View source at https://github.com/githubnext/agentics/tree/828ac109efb43990f59475cbfce90ede5546586c/workflows/daily-test-improver.md.