feedback5 WD: the sim fields a 补位 stand-in — getChess(id, { standIn: true }) over data/backups.json, PlayerBattleInput standIn: true, kits by the stand-in's charId (never the replaced operator's), kits/ops/standin-<codename>.js registry, harness standIn

- simdata: DataSource keeps `backups` (rawBackups follows the fallback chain); getStandIn = shared/standIn.js
  standInRecord normalised (the chess's ids / bonds / 特质 / tier, the stand-in's body, def.standInFor); a PRESET / DIY
  chess or a source without backups fields itself; the per-battle view maps id-only lookups.
- spec.js keeps `standIn` only when exactly true (never on a token); Battle passes it to getChess; syncUnitLoadout
  carries it; UnitInfo `standInFor`.
- content/index.js kitOf: a stand-in's kit is KITS[def.charId] only; no default skill (a stand-in kit writes `skills`);
  without a kit the generic kit plus genericTalents. kits/index.js STANDIN_KIT_FILES / STANDIN_KITS, merged after the
  tier groups (old keys keep their order; golden unchanged).
- server/data.js and tools/setup.mjs expect backups.json.
- test/content/standin.test.js: the plumbing and the eight 预备干员 on all 28 chess records they replace.

server/sim/spec.js

@@ -20,6 +20,8 @@
 // the default). createBattleFromSpec hands the Battle a per-battle data view (withUnitLoadouts) that resolves each
 // operator def — and its summons — for the loadout of its chess (simdata getChess(id, loadout) / getToken(id, owner,
 // ownerLoadout)); an explicit loadout argument always wins over the view's per-chess lookup.
+// 补位 (DATA.md §18): an operator entry with `standIn: true` (kept only when exactly `true`) is fielded as its chess's
+// stand-in (simdata getChess(id, { standIn: true }); its skill / module are the chess's backup selection).
 
 import { Battle } from './Battle.js';
 import { toDataSource, withUnitLoadouts } from './simdata.js';
@@ -76,11 +78,15 @@ export function buildBattleSpec(o = {}) {
 
 const LOADOUT_ID = /^[A-Za-z0-9_\-]{1,64}$/;
 
-/** Keep a unit's `skillIndex` / `moduleId` only when well-formed (the data layer checks legality). Mutates `u`. */
+/**
+ * Keep a unit's `skillIndex` / `moduleId` only when well-formed (the data layer checks legality) and `standIn` only
+ * when exactly `true` (补位). Mutates `u`.
+ */
 export function sanitizeUnitLoadout(u) {
   if ('skillIndex' in u && !(Number.isInteger(u.skillIndex) && u.skillIndex >= 0 && u.skillIndex <= 9)) delete u.skillIndex;
   if ('moduleId' in u && !(typeof u.moduleId === 'string' && LOADOUT_ID.test(u.moduleId))) delete u.moduleId;
-  if (u.kind === 'token') { delete u.skillIndex; delete u.moduleId; }
+  if ('standIn' in u && u.standIn !== true) delete u.standIn;
+  if (u.kind === 'token') { delete u.skillIndex; delete u.moduleId; delete u.standIn; }
   return u;
 }