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/battle/players.js

@@ -102,8 +102,11 @@ export class BattlePlayers {
       return u;
     }
     // the unit's own loadout (DESIGN §16): an entry without loadout fields is the DEFAULT — never another player's
-    // choice for the same chess id in a multi-player field (the per-battle data view maps id-only lookups)
-    const def = this.data.getChess(inp.chessId, { skillIndex: inp.skillIndex ?? null, moduleId: inp.moduleId ?? null });
+    // choice for the same chess id in a multi-player field (the per-battle data view maps id-only lookups); `standIn:
+    // true` fields the chess as its 补位 stand-in (simdata getStandIn: the stand-in's body, the chess's identity)
+    const lo = { skillIndex: inp.skillIndex ?? null, moduleId: inp.moduleId ?? null };
+    if (inp.standIn === true) lo.standIn = true;
+    const def = this.data.getChess(inp.chessId, lo);
     if (!def) { this.log(`unknown chess ${inp.chessId}`); return null; }
     const u = this._makeAlly(ps, def, 'op', r, c, { uid: inp.uid, dir });
     u.items = [...(inp.items ?? [])];