Fleeing the way one came, and seeing danger before it strikes

After death zones: 86 deaths in 20 minutes (vs 99), 39 level-ups (vs 15). But one flight in three ended badly, as the player ran blindly into other monsters. It now retreats along the path it just walked, flees a little earlier, and spots rares, elites and much stronger aggressive monsters on sight to keep away before being attacked.

Measurement (20 min, killer logged)

86 deaths for 41 players; 12 caused by rares (Warlord Kolkanis 6, Bjarn 5).
100 flights, 36 of which ended in death: the “away from attackers” direction often led into other monsters.
39 deaths with 2 to 4 attackers (adds).

Fixes

Retreat along the walked path: each character keeps a trail of its recent out-of-combat positions (every 5 s, 15 points). When fleeing, it heads for the most recent trail point more than 35 m from the attackers: walkable, already cleared ground. Fleeing “the other way” is now a last resort.
Flee earlier: at 40 % health against several attackers, 35 % otherwise (30 % before).
Seeing danger: every 5 s, a look around within 40 m. A rare or elite close to one's level, or an aggressive monster 3 levels higher, creates an area to avoid (45 m for 20 min for a rare; 25 m for 8 min otherwise): quests, hunting and service NPCs steer away from it before any fight.

Cost measurement

The server's idle CPU cost (idle_cpu_ns_per_s) is now the minimum of second-by-second samples over 25 s, before autonomous players arrive: it no longer counts the end of initialisation.