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.

docs/design/network.md

@@ -23,7 +23,14 @@ S→C:
 - NOTE: game time in `b.snap`/`b.ev` is carried as **`gt`** (the frame's `t` is the message type).
 - Active finite zero-SP timed skills display `sp=timeLeft`, `spMax=duration` and `UF.SKILL`; after end they display
   `0/0`. Snapshot display capacity does not change runtime SP/cost.
-- `b.snap` — `{ fieldId, gt, units: [[id, x, y, hp, maxHp, sp, spMax, flags, anim]] , dp, killed, total, down?, elem? }` 20 Hz (a countdown summon's `hp` is maxHp × the share of its life left, §25.16.5). Optional, only when non-empty (§18.3): `down: [[id, respawnAt (game s), respawnTime (s), state, row, col]]` — knocked-out operators waiting to redeploy, `state` 0 counting | 1 timer done, waiting for DP | 2 timer done, its tile taken — a safeguard, no ally deploys there (sim/constants.js `DOWN_STATE`); `row, col` = the tile it lies on and comes back on (§21.24); `elem: [[id, element, fill, cooldownEnd (game s), cooldown (s)]]` — the one gauge a unit shows: the fullest (ties by the official element id 神经 < 侵蚀 < 灼燃 < 凋亡), fill with 2 decimals rounded DOWN and kept at 0.01–0.99 outside a burst (§20.8); during a 爆发冷却 the bursting element with fill 1 and the cooldown numbers (else 0, 0)
+- `b.snap` — `{ fieldId, gt, units: [[id, x, y, hp, maxHp, sp, spMax, flags, anim]] , dp, killed, total, down?, elem?, stand?, standCut? }` 20 Hz (a countdown summon's `hp` is maxHp × the share of its life left, §25.16.5). Optional, only when non-empty (§18.3): `down: [[id, respawnAt (game s), respawnTime (s), state, row, col]]` — knocked-out operators waiting to redeploy, `state` 0 counting | 1 timer done, waiting for DP | 2 timer done, its tile taken — a safeguard, no ally deploys there (sim/constants.js `DOWN_STATE`); `row, col` = the tile it lies on and comes back on (§21.24); `elem: [[id, element, fill, cooldownEnd (game s), cooldown (s)]]` — the one gauge a unit shows: the fullest (ties by the official element id 神经 < 侵蚀 < 灼燃 < 凋亡), fill with 2 decimals rounded DOWN and kept at 0.01–0.99 outside a burst (§20.8); during a 爆发冷却 the bursting element with fill 1 and the cooldown numbers (else 0, 0)
+  Optional, only when non-empty (PR #381; display metadata, SIM §9): `stand: [[id, until]]` — the game time an enemy's
+  attack recovery ends (`atkStandUntil`; enemies alive, deployed, visible, neither feared nor stunned): when it falls
+  between two snapshots the renderer holds the position until then and interpolates the rest (HP / SP unchanged), and
+  extrapolates nothing while the newest snapshot still holds a stand; `standCut: [[id, at]]` — the latest time each
+  listed enemy's recovery was cut or ignored (失衡, fear, stun, hiding, leaving): an interval with a cut inside it stays
+  linear. A newest snapshot showing a death, a stun or a block is not extrapolated. Old snapshots without them
+  interpolate linearly; nothing is inferred from the attack animation.
 - `b.ev` — `{ fieldId, ev: [ ... ] }` event tuples: `['spawn', UnitInfo]`, `['atk', srcId, tgtId, projKind]`, `['dmg', tgtId, amount, type]`, `['heal', tgtId, amount]`, `['skill', id, on:0|1]`, `['die', id, reason]` (reason `'killed'`, `'retreat'`, `'expired'` …; only `'killed'` plays an operator's knock-down sound), `['status', id, key, on]`, `['fx', kind, x, y, extra]` (`'hitCap' {id, n}` = a cancelled 限伤 hit, drawn as nothing, §20.12; `extra.form` = the unit's model form from then on (an enemy's mode, a 傀儡师's 替身 §22.11) — `shared/protocol.js fxForm`, state like a spawn: never dropped by the client, §21.4), `['layer', playerId, bondId, n]`, `['bounty', playerId, coins]`, `['deploy', id]`
 - `m.toast {kind, text}` · `m.ticker {text, id, type, priority, playerId}` (the strip plays the highest priority first, §21.10) · `m.emote {playerId, id}` · `m.result {...}`
 - `m.unitStats {seq, round, units: [unitStatsEntry]}` — the answer to `g.unitStats` (`seq` echoed): every own board operator / summon by uid with `{id, uid, defId, hp, alive, maxHp, atk, def, res, interval, blockCnt, moveSpeed, range?, base: {…same}}` (shared/protocol.js `unitStatsEntry`; `range` = an ally's live range grid, facing RIGHT, never a target-selection grid, §21.16) as its next battle starts (§18.5)