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/kits/ops/chess_char_5_09-cetsyr.js

@@ -4,6 +4,7 @@
 import { COLS } from '../../../constants.js';
 import { rotateOffset } from '../../../dir.js';
 import { AURA_IV, AURA_DUR, num, talent, traitBb, skillGrid, isOp, leaderOf, whileOn } from '../shared/tier5.js';
+import { hypot, sin, cos } from '../../../detmath.js';
 
 /** 魔王 T1 微尘: collision radius of one mote (PRTS 备注 0.4); orbit radius / speed come from the talent bb. */
 const MOTE_HIT_RADIUS = 0.4;
@@ -82,11 +83,11 @@ export default {
               const ang = spd * t + (2 * Math.PI * k) / cnt;
               // the orbit turns with his direction: angle 0 = straight ahead, π/2 = his left hand
               const [fr, fc] = unit.fwd, [lr, lc] = rotateOffset(1, 0, unit.dir);
-              const mx = unit.x + orbit * (fc * Math.cos(ang) + lc * Math.sin(ang)), my = unit.y + orbit * (fr * Math.cos(ang) + lr * Math.sin(ang));
+              const mx = unit.x + orbit * (fc * cos(ang) + lc * sin(ang)), my = unit.y + orbit * (fr * cos(ang) + lr * sin(ang));
               let hit = null, hd = Infinity;
               for (const a of cands) {
                 if (a.findBuff('cetsyr:mote')) continue;
-                const d = Math.hypot(a.x - mx, a.y - my);
+                const d = hypot(a.x - mx, a.y - my);
                 if (d <= MOTE_HIT_RADIUS + 1e-9 && d < hd) { hd = d; hit = a; }
               }
               if (!hit) continue;