test: document terrain modifier semantics

[MichaelFisher1997]

Summary

• Add a pure TerrainModifier.applyHeight helper to define modifier height semantics before live pipeline integration.
• Add deterministic tests for height_amplitude, smoothing, clamp_to_sea_level, height_offset, sea-level/high-elevation edges, and combined behavior.
• Register the new terrain modifier tests in the worldgen test suite.

Verification

• nix develop --command zig fmt modules/world-worldgen/src/biome_registry.zig modules/world-worldgen/src/terrain_modifier_tests.zig modules/world-worldgen/src/root.zig src/tests.zig
• nix develop --command zig build test

Fixes #649

[github-actions]

📋 Summary

Linked Issue: #649 — "Worldgen Phase 0: add terrain modifier tests"

The PR fully addresses issue #649 by:

• Defining expected behavior for height_amplitude, smoothing, clamp_to_sea_level, and height_offset
• Including edge cases near sea level (62.0) and high elevation (144.0, 180.0, 226.0)
• Providing deterministic tests that require no chunk rendering
• All existing tests continue to pass (zig build test exits cleanly)

PR Purpose: Adds a pure TerrainModifier.applyHeight helper function to biome_registry.zig and comprehensive unit tests documenting the semantics of each terrain modifier field before live pipeline integration. Scope is focused and well-contained — one helper function, one new test file, and two registration imports.

Overall Quality: High. Code follows existing conventions, math is correct, tests are deterministic and descriptive, formatting passes zig fmt, and the full test suite passes.

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📌 Review Metadata

• Reviewed Commit SHA: 28e1da6ff057ff52cb56928da7d4ea0b700b028d
• Reviewed PR: test: document terrain modifier semantics #665
• Linked Issues: Worldgen Phase 0: add terrain modifier tests #649 — fully satisfied

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🔴 Critical Issues (Must Fix - Blocks Merge)

None identified.

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⚠️ High Priority Issues (Should Fix)

None identified.

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💡 Medium Priority Issues (Nice to Fix)

None identified.

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ℹ️ Low Priority Suggestions (Optional)

None identified.

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📊 SOLID Principles Score

Principle	Score	Notes
Single Responsibility	9	applyHeight does one thing; each test covers one modifier
Open/Closed	7	Struct is open for new fields, but applyHeight would need updates
Liskov Substitution	8	Not directly applicable; pure function behavior is consistent
Interface Segregation	9	Clean, focused API with only two parameters
Dependency Inversion	9	Zero external dependencies; fully pure
Average	8.4

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🎯 Final Assessment

Overall Confidence Score: 95%

Confidence Breakdown:

• Code Quality: 95% (well-structured, follows conventions, pure function)
• Completeness: 100% (all acceptance criteria from Worldgen Phase 0: add terrain modifier tests #649 met)
• Risk Level: 5% (additive only — new helper + tests, no existing behavior changed)
• Test Coverage: 95% (six focused tests covering defaults, individual modifiers, and combinations)

Merge Readiness:

• All critical issues resolved
• SOLID average score >= 6.0
• Overall confidence >= 60%
• No security concerns
• Tests present and passing

Verdict:

MERGE

Clean, focused test PR that documents terrain modifier semantics and satisfies all acceptance criteria for #649.

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  "reviewed_sha": "28e1da6ff057ff52cb56928da7d4ea0b700b028d",
  "critical_issues": 0,
  "high_priority_issues": 0,
  "medium_priority_issues": 0,
  "overall_confidence_score": 95,
  "recommendation": "MERGE"
}

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