Auto-attack: next target, melee/ranged rule after arts; chain range = cast range

- autoattack: when the target dies, the nearest enemy within close range
  (contact distance + a step) takes over; after an art the hero auto-attacks
  if the art was melee (walked up / cast close by), or ranged with a ranged
  weapon, or ranged with an enemy already in melee range; measured action
  codes and weapon classes in game/engine/orders.h
- chainlightning: jumps reach Blitzschlag's cast range (20 ray segments of
  30, the art code's hit check) via the shared NearestHostile search
- guards: burning bone render hook had the wrong signature (device plus a
  4x4 matrix by value, ret 0x44) and corrupted the stack when fire arrows hit
- crash reports follow the ebp chain before the raw stack scan

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/auto-attack.md

@@ -52,3 +52,36 @@ wind-up, 0.64 s attack, 0.43 s recovery).
   with a held button; the tick only restarts the attack after casts.
 - Self / ally arts pointed at an enemy lose their target
   (`src/mods/arttarget.cpp`) and therefore do not start auto-attack.
+
+## Next target, and auto-attack after arts (2026-10-16)
+
+User requests: when the target dies, go on with the next enemy close by;
+after a melee art always auto-attack, after a ranged art only with a ranged
+weapon.
+
+Measured with a temporary log (distance hero → target when the hero started
+the swing or cast, battlemage with a staff):
+
+- +0x150 low word: 1 walking (also walking up to a target), 3 weapon attack,
+  4 casting a spell. The "1 art" above was the walk up; 8 (seen after it on
+  2026-10-15) is presumably a combat move. Names in `game/engine/orders.h`.
+- Weapon swings started at 117..149 after walking up from up to 1382: the
+  game's contact distance (`0x4dbaa0`, mean of both body radii by object
+  type; heroes 110 with a weapon, 80 without).
+- Spells (Blitzschlag 0x21, art 5) started at once from 647..803: no walk-up.
+  Their cast limit, if any, is beyond that.
+
+Rules (`autoattack.cpp`):
+
+- Close range = `ContactDistance(hero, hero) + 100` (≈ 210) with a melee
+  weapon; 600 with a ranged one (TODO: measure a ranged hero). Ranged weapon =
+  weapon class (`0x546df0`) 6 throwing, 7 bow, 12 crossbow, 13 pistol.
+- The target died: the nearest living hostile creature within close range
+  (`game::NearestHostile`) becomes the target, else auto-attack stops.
+- An art order (not a buff / ally / corpse art) is watched until the hero
+  starts it (action 4 or 8). It is melee if the hero walked first, ranged if
+  it starts farther away than contact distance + 100, else as remembered for
+  that art (default melee). Melee: auto-attack its enemy target, or the
+  nearest enemy close by. Ranged: the same with a ranged weapon; with a melee
+  weapon only an enemy already in close range (the art's target if it is,
+  else the nearest), otherwise auto-attack stops. Until the art starts, no attack orders are sent.