Dwarf arts: Kanonenschuss stuns without knockback, Mörsergranate radius grows

Kanonenschuss: the stun no longer plays the hit motion or pushes the
target; stunned creatures stand still for 1.5 s. The impact effect only
shows on targets that did not resist, and the ray reaches 1800 for the
wider view. Mörsergranate: the impact radius grows by a tenth of its size
every 5 skill levels. Art levels come from a shared helper.

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

docs/dwarf-arts.md

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+# Dwarf arts: Kanonenschuss and Mörsergranate
+
+## Requests (2026-10-25 / 2026-10-26)
+
+- Kanonenschuss (art 0x43f, `gui_spells_kanone`): "remove the knockback,
+  instead it can be just a stun" (chosen: no push, only a stun); the range
+  increased for the wider view; the stun particles not on targets that
+  avoided the stun. The game's stun resistance stays (2026-10-26: "we dont
+  ignore anything, the skill is fine for now").
+- Mörsergranate (art 0x43e, `gui_spells_moerser`): "the radius of the
+  explosion should increase every 5 skill levels".
+
+## Measured
+
+- The cannon's code is the combat move function `0x5145d0`, case 0x43f. Its
+  ray: `cmp edi,19h` at `0x517389`, 25 steps of 40 = 1000 range. Hostile
+  targets get `cEvent_creature` 5 from `0x51768d`.
+- Stun chance `0x4fc810(level, creature)` = level × 5 / creature level × 100
+  (`UI_STAT_STUNNCHANCE`). On a successful roll: `0x5936e0(MOTION_HIT_A 0xaf,
+  3.0, 0.25)` at `0x517709` (pushes from `0x5176f8`), then the stun order
+  `cEvent_creature` 3 with +0x14 = 100, sent by `call [eax+18h]` at
+  `0x5177aa` (returns to `0x5177ad`).
+- The stun *is* the knockback. `cCreature::ReceiveOrder` `0x52e400` case 3:
+  first the resistance `vf24(0x50)` (`0x55d0a0`: flag +0x4f0 & 0x1000 resists
+  2 in 3, effect 0x35d a percentage); otherwise push left +0x24d = 100, flag
+  +0x200 |= 0x20000, attacker +0x259, ResetToIdle. `cCreature::Update` branch
+  `0x594c82` moves a creature with that flag away from the attacker and lowers
+  the push left by each step (`0x594deb`), measured about 100 units in 0.3 s;
+  at 0 the flag is cleared.
+- The impact effect `TYPE_FX_DWARF_SHOOT_IMPACT` (0x47f) is created on every
+  hit target by `CreateAt` at `0x517855` (target in ebx), resisted or not.
+- Mörsergranate: the grenade (type 0x3fa) lands and creates
+  `TYPE_FX_GRENADEIMPACT` (0x3fc), which gathers its targets with
+  `cObjectManager 0x5ff820` (called from `0x5ab400` at `0x5ab63d`): a creature
+  is hit when its distance is below the impact's size (150, type table
+  `0x428bb0`) plus its own type's size.
+
+## The mod (`src/mods/dwarfarts.cpp`)
+
+- The HIT_A motion is jumped over (`0x5176f8`: `jmp` past the call).
+- The push step at `0x594deb` calls `PushStepThunk`: creatures the cannon
+  stunned (order 3 from `0x5177ad`, kept with an end time) move by 0 and keep
+  their push left above 0 for 1.5 s, so they stand still, then carry on.
+- The impact effect is created only on targets in the stun state.
+- The ray gets 45 steps (1800); confirmed to reach across the widened view.
+- The impact's gather call gets a radius of size × (1 + 0.1 × (level / 5)),
+  with the owner's Mörsergranate level (`game::ArtLevel`). The growth 0.1 per
+  step is our choice; not yet seen in the game (Borf's level is 2).