B key toggles bBuildMode. While active, Tick line-traces from the
character's eye height along its forward vector, breaks the hit
result, and snaps the impact point to a 200-unit grid via
Vector_SnappedToGrid, storing the result in SnappedLocation. No
visual feedback or placement yet (next: ghost preview, then
place/remove).
Uses BreakHitResult (a multi-output-pin CallFunction on
GameplayStatics) to extract struct fields, since a dedicated
"BreakStruct" node type isn't supported by this tool -- works fine
as a plain function call.
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