Movement commands now access the zone through player.location instead of
a module-level world variable. send_nearby_message uses
zone.contents_near() to find nearby entities, eliminating the need for
the global players dict and manual distance calculations.
Tests updated to create zones and add entities via location assignment.
The variant handler now supports prefix matching for directional variants.
This allows 'pa hi' to match 'parry high', 'pa lo' to match 'parry low', etc.
Implementation:
- First tries exact match on variant key
- Falls back to prefix matching if no exact match
- Returns unique match if exactly one variant starts with the prefix
- Shows disambiguation message if multiple variants match
- Shows error with valid options if no variants match
Tests cover exact match, prefix match, ambiguous prefix, no match,
single-char prefix, case-insensitivity, and preservation of target args.
