feedback7: the battle sim uses engine-independent math — Chrome, Firefox, Safari and the server agree bit for bit (PR #373 by @Cloudnyco)

- server/sim/detmath.js: hypot (sqrt of the squares, rescaled outside 2^±500), powi (integer powers in double-double,
  one rounding), sin / cos (fdlibm 5.3) and atan2 (fdlibm / FreeBSD msun) built only from correctly rounded IEEE
  operations; the sim's Math.hypot / sin / cos / atan2 / pow calls go through it (65 files); eslint.config.js forbids
  the approximated Math functions under server/sim and test/sim/detmath.test.js scans for them.
- sin / cos / atan2 are the algorithms V8 runs in Node, so the server's results stay; only hypot differs from V8's.
  Golden: 2 moved — diy-027 (a hypot distance, damage +80) and coop3-ABYSS-5 (a later card pick from round 9, same end).
- Applied unchanged after review (Grok static review: MERGE; the diff read in full: no network, no new dependency).
- Tests: broad node --test 5155 / 5155 with the new file tracked (detmath 7 / 7, package 10 / 10); lint 0 errors,
  typecheck, check:imports.

server/sim/content/enemies/special.js

@@ -12,6 +12,7 @@ import {
   unblockable, runWhenHit, blockWeight, taunt, maxTargets, ep, nthAttackPower, lowHpBuff, deathBoom, setFloat, float,
   reborn, frontGuard, faceMove, unbalanced, skill, kitEp, kitPrisoner, kitStun3,
 } from './archetypes.js';
+import { hypot } from '../../detmath.js';
 
 // ---------------------------------------------------------------------------------------------------------------
 // constants (numbers that exist nowhere in the data)
@@ -245,7 +246,7 @@ export const SPECIAL_KITS = Object.freeze({
   enemy_1183_mlasrt: (ab) => [ep('erosion', T(ab, 'EpDamage.attack@ep_damage_ratio') ?? 0), nthAttackPower(nthOf(ab.sk.PowerAttack), (ab.sk.PowerAttack && ab.sk.PowerAttack.bb.atk_scale) || 1)], // 无胄盟清扫小队 · erosion; every 4th attack ×1.5
   enemy_1273_stmgun_2: (ab) => {                                     // 高准度伦蒂尼姆城防自行炮 · locks the highest max-HP unit in range, bombards the highest HP% on its 9 tiles
     // the allies in its range (the engine's ranged reach: radius + the ally collider)
-    const inRange = (b, e) => allTargets(b, e).filter((a) => Math.hypot(a.x - e.x, a.y - e.y) <= (e.base.rangeRadius || 0) + ALLY_COLLIDER_RADIUS + 1e-9);
+    const inRange = (b, e) => allTargets(b, e).filter((a) => hypot(a.x - e.x, a.y - e.y) <= (e.base.rangeRadius || 0) + ALLY_COLLIDER_RADIUS + 1e-9);
     return [skill(ab.sk.Cannon, (b, e) => {
       const lock = inRange(b, e).sort((p, q) => q.s.maxHp - p.s.maxHp)[0];
       if (!lock) return;
@@ -279,7 +280,7 @@ export const SPECIAL_KITS = Object.freeze({
     spawn(b, e) { watchDeaths(b, e); },
     otherDeath(c, b, e) {
       const u = c.unit;
-      if (!u || u === e || c.reason !== 'killed' || Math.hypot(u.x - e.x, u.y - e.y) > (T(ab, 'Attack.range_radius') ?? TORTURER_RADIUS) + 1e-9) return;
+      if (!u || u === e || c.reason !== 'killed' || hypot(u.x - e.x, u.y - e.y) > (T(ab, 'Attack.range_radius') ?? TORTURER_RADIUS) + 1e-9) return;
       b.heal(e, e, e.s.maxHp * (T(ab, 'Attack.hp_ratio') ?? 0), { self: true });
       b.addBuff(e, { key: 'ab:torture', refresh: 'stack', stacks: 1, maxStacks: T(ab, 'Attack.max_stack_cnt') ?? 1, persist: true, mods: { atkPct: T(ab, 'Attack.atk') ?? 0 } });
     },