System: movement

Player (agent) movement system.

Attempts to move the controlled agent to next_pos applying effect logic:

1. If the agent has an active Phasing effect (consuming a usage/time limit) it ignores blocking components entirely.
2. Otherwise the move is allowed only if destination is in-bounds and not blocked by Blocking/Pushable/Collidable entities (push handling occurs in a separate system before this is called).

Returns the original State if movement is not possible; otherwise a new State with updated position (and possibly decremented usage limits).

movement_system(state, entity_id, next_pos)

Move agent one tile if allowed.

Parameters:

Name	Type	Description	Default
state	State	Current state.	required
entity_id	EntityID	Agent entity id (ignored if not an agent).	required
next_pos	Position	Desired destination position.	required

Returns:

Name	Type	Description
State	State	Same state if blocked / invalid or updated with new position.