[Copilot]

M_RefreshHeatmap was called every frame from unit_changeangle, unconditionally invoking CM_BuildHeatmap. The 4-slot LRU cache inside CM_BuildHeatmap helped for identical goals, but with >4 concurrent move groups or attack targets it thrashed constantly — causing bake_flow_field + build_heatmap to re-run on every frame and account for ~49% of total CPU time.

Changes

• common/routing.c — Added CM_ActivateCachedFlow(DWORD generation): looks up a cached flow field by generation number and sets active_flow without triggering a rebuild. O(N) over 4 slots.

• common/common.h — Declared CM_ActivateCachedFlow.

• games/warcraft-3/game/g_monster.c — M_RefreshHeatmap: For fixed waypoints (non-SVF_MONSTER goals), skip CM_BuildHeatmap if route->heatmap2 is already set and the generation is still cached — the full rebuild only happens once per move order. Monster targets (chased enemies) continue to rebuild every frame since their position changes.

if (!(route->svflags & SVF_MONSTER) &&
    route->heatmap2 &&
    CM_ActivateCachedFlow(route->heatmap2)) {
    return route->heatmap2;
}
route->heatmap2 = CM_BuildHeatmap(route);

Waypoint_add already zeroes heatmap2 on allocation, so each new move order triggers exactly one rebuild and all subsequent frames hit the fast path.