Environment::removeEntity leaves an entity present when it was added twice to one location #70

Summary

Grid::removeEntity (src/grid.cpp:96) calls Location::removeEntity once per location, and Location::removeEntity (src/location.cpp:33) erases only the first matching pointer. An entity added twice to the same location therefore keeps one pointer in that location after removal, even though its ids have been reset.

addEntity and addEntityToLocation are documented as unchecked, so the double add itself is expected. The inconsistent state after removal is what is reported here.

Reproduction (traced through the source)

Environment environment(0, "Earth", 2);
Entity entity(0, "Daniel");
Location& location = environment.getGrid()->getLocationByCoordinates(0, 0);
environment.addEntityToLocation(entity, location);
environment.addEntityToLocation(entity, location);
environment.removeEntity(entity);

After removeEntity:

• environment.isEntityPresent(entity) is true and environment.getNumEntities() is 1.
• entity.getEnvironmentId() and entity.getGridId() are -1, and entity.getLocationId() is "N/S".
• environment.moveEntityUp(0) throws std::runtime_error, because moveEntityInDirection calls getLocation("N/S") outside its try block (src/environment.cpp:127). The move methods are documented as throwing only when entityId names no entity in the environment.
• moveEntityToNewLocation has the same root cause: its removal leaves the old pointer behind, so the entity ends up stored in both locations.

An entity added once each to two different locations is removed completely, because the loop visits both locations. Only the same-location case is affected.

Suggested fix

Grid::removeEntity could repeat the removal until the location no longer reports the entity present, or Location::removeEntity could erase every pointer with a matching id. Either choice should be weighed against the id-based matching described in the README's "Entity Identity" section, since a same-id twin stored in that location would be erased too.

This issue was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

drafted by Claude on behalf of Daniel Stephenson