Enhanced findDirectionalStadiums() to prevent including games at
stadiums that are beyond the destination city.
Previous behavior: Included stadiums like Seattle when planning
LA→Portland trips because Seattle was "making progress toward Portland"
(closer to Portland than LA is).
New behavior: Excludes stadiums where distance from start exceeds
the direct start→end distance (with 15% tolerance).
Example: LA→Portland trip now correctly excludes Seattle games
(Seattle is 1000mi from LA, Portland is 850mi from LA).
Fixes test: corridor_MultipleGamesMixed_FiltersCorrectly()
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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