feedback7 R22-RENDER: an enemy standing out its attack recovery is drawn standing — the snapshot carries stand / standCut and the interpolator holds the position until the recovery ends (PR #381 by @ZiyueW1116, supersedes #307 / #314); golden: unchanged

Since 0.2.0 the sim stands an unblocked enemy for the rest of its attack clip (ai.js attackStand → atkStandUntil),
but render/interp.js lerped x/y over the whole snapshot gap, so the view slid through a recovery the sim held
(repro: a real 隐形弩手, snapshots 4.9 / 5.0, stand until 4.934 — sampled at 4.917 it slid at vx −0.2).

The snapshot now carries, only when non-empty, `stand: [[id, until]]` (atkStandUntil of enemies alive, deployed,
visible, neither feared nor stunned) and `standCut: [[id, at]]` (the latest time each listed enemy's recovery was cut
or ignored: a displacement, fear, a stun, hiding, leaving — Battle._cutAttackStand, display metadata the battle never
reads). sample() holds the older position until `until` and interpolates the rest (HP / SP keep the whole interval),
stays linear when the newer snapshot records a cut inside the interval, and extrapolates nothing for a newest snapshot
that shows a stand, a death, a stun or a block. Teleports and redeploys still snap first; old snapshots without the
fields interpolate as before.

Substantially @ZiyueW1116's code (PR #381), authored as theirs. Changed on review: the docs (SIM §9, design/network.md)
and code comments in English like the rest of them; the snapshot builds its listed-id set only when an enemy has a cut
to report.

Golden: unchanged — the digest canon hashes neither field and the sim's timing does not move (all 283 scenarios match).

Tests: test/render/attack-recovery-interp.test.js (new, 25: metadata validation, hold-then-slide, cuts, legacy
snapshots, extrapolation guards, real 隐形弩手 / Weedy push-kill / stun / freeze / sleep / levitate / block / fear
battles) 25/25; render/interp 16/16; sim battle, perf, robustness, downelem 69/69.

server/sim/ai.js

@@ -535,6 +535,7 @@ export function updateEnemy(b, e, dt) {
   if (!e.alive) return;
   // hidden (teleporting) enemies only advance wait legs
   const stunned = e.s.flags.stun;
+  if (stunned || e.hidden || e.s.flags.fear) b._cutAttackStand(e);
   const prevCd = e.atkCd;
   if (e.atkCd > 0 && !stunned && !e.hidden) e.atkCd = Math.max(0, e.atkCd - dt);
   // a stun / freeze / sleep / 浮空 — or leaving the field — takes the enemy out of its attack: a swing short of its damage
@@ -644,6 +645,7 @@ function advanceRoute(b, e, dt, R, standing = false) {
       continue;
     }
     if (leg.t === 'disappear') {
+      b._cutAttackStand(e);
       b._setHidden(e, true);
       e.atkStandUntil = -Infinity; standing = false;   // off the field: its attack clip is over
       R.legIdx++; R.pts = null;