Worldgen Phase 3: validate region role interaction with biome selection

[MichaelFisher1997]

Parent: #646

Phase

Phase 3: Compatibility and tuning

Goal

Ensure the macro-region system still creates intentional pacing after biome terrain and selector changes.

Tasks

• Validate transit, destination, and boundary regions under the new terrain modifier path.
• Confirm destination focus still affects lakes, forests, mountains, rivers, vegetation, and height drama.
• Check that biome selection does not fight region controls too strongly.
• Add baseline/report coverage for region-role effects if practical.

Acceptance Criteria

• Transit regions remain calmer/flatter on average.
• Mountain destination regions show clear height drama.
• Forest destination regions show higher vegetation density.
• Boundary regions still provide separation/roughness.

Dependencies

• Should follow terrain modifier integration and initial selector migration.

Parallelization

Can run in parallel with adjacency tuning and debug snapshot work.

[github-actions]

Comment posted to issue #649. The analysis noted that biome selection runs independently from region controls (no current mechanism for region role to bias biome ID), which aligns with the "does not fight region controls" goal, but should be verified. Also identified that baseline/report coverage for region-role effects is a gap.

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