feedback1 WE: 鸭爵 swaps stay on the player's half of a pair leader field

- A pair Final Assault / Hidden Core field has one spawn list that both
  players' handlers edit; each player's 0-2 swaps now come only from the
  enemies whose route ends on that player's half (the half rule of the
  field's bounties). Match passes the wave's routes and the player's side
  ('L' / 'R', null on a one-player field) in the boss / hidden
  onBattleStart event; docs/META.md documents the two fields.
- The comment justifying elite eligibility was wrong (the leader rounds'
  escorts are a mix, about two thirds elites, not all elites); reworded
  with the measured numbers and kept [ASSUMED].
- The pair-field test now drives the real match path (Final Assault, then
  the Hidden Core it unlocks) instead of dispatching by hand; a unit check
  covers the half filter.

server/sim/content/bands/meta.js

@@ -20,7 +20,8 @@
 //   up_shop_add_special_goods {count,choice,pool}      凯瑟琳   every level-up: pick 1 of `count` items of pool (free)
 //   coin_carry_over {capital,interest,max}             坎诺特   leftover ≥ capital at round start → +min(max, ⌊left/capital⌋×interest) income
 //   round_start_all_player_change_enemy_2              鸭爵     global: every alive player's battle from `round` (own + teammates;
-//                                                                normal, Final Assault, Hidden Core): 0–2 enemies → enemylist
+//                                                                normal, Final Assault, Hidden Core — on the player's half of a
+//                                                                pair field): 0–2 ground enemies → enemylist
 //   round_start_activate_char_chess_effect_in_board    铃兰     round start: 获得时 traits of the right-most (then bottom-most) board op with one
 //   first_sell_char_chess_exchange_char_chess_in_shop  巫恋     first sale of a normal op per round: swapped with a random shop chess (no funds)
 //   round_start_gain_char_chess_in_shop_every_n_round  松桐     round % n = 0: a random shop chess for free (its slot empties)
@@ -29,6 +30,7 @@
 //   preparation_start_add_special_goods_every_n_round  娜仁图亚 round % n = 0: pick choice_cnt of refresh_cnt items of pool (free)
 // "进入休整期时" / "回合开始时" = onRoundStart (research 01 §5 step 6).
 
+import { GEO } from '../../../../shared/constants.js';
 import { buffsOf, num, bandRecord, gameData } from '../support/index.js';
 import { metaBonds } from '../support/meta.js';
 import * as garrisons from '../garrisons.js';
@@ -354,37 +356,56 @@ K.preparation_start_add_special_goods_every_n_round = (ps) => ({
 // player or a teammate: from round `round`, in the normal battle, the Final Assault and the Hidden Core (PRTS 卫戍协议：盟约
 // 下半/PRTS盟约记录 鸭爵 备注 "每回合将有0~2名敌人被替换为上述敌人之一…且在最终回合和隐秘核心回合中仍然生效"; the 联防 phase
 // replaces nothing: its enemies are leaks, which keep their bounty). min..max (0–2, uniform [ASSUMED]) of the player's
-// ground enemies from the `minweight`–`maxweight` share of the wave (time order) [ASSUMED reading of the two weights]
-// — any wave enemy but the leader, its parts, bounties, earlier swaps and uncounted units: normal or elite, as the
-// Final Assault's escorts are all elites; flyers stay [ASSUMED: the four are ground units and a FLY action's route is
-// a FLY route] — become a random enemylist enemy (the act2 `_2` versions) at the replaced unit's time and route, worth
-// DUCK_COINS to its killer (bounty, also in 联防). A boss field's two players edit the field's one list in turn, so each
-// gets its own 0–2. The originals never exist, so none of their death / kill / leak effects happen. Reaching the
-// protection point costs 1 LP ("但进入保护目标点将减少1点目标生命值": the enemies' data lpr, tools/build-data.mjs).
+// ground enemies from the `minweight`–`maxweight` share of the player's enemies (time order) [ASSUMED reading of the two
+// weights] — any wave enemy but the leader, its parts, bounties, earlier swaps and uncounted units. Elites are eligible
+// too [ASSUMED: the text names no rank; one rule for every battle; about two thirds of the leader rounds' escorts in that
+// share are elites, so a NORMAL-only rule would leave most Final Assault halves without a candidate — ≈ 80 % instead of
+// ≈ 36 % of the R14 pair-field halves over 40 seeds]. Flyers are never swapped [ASSUMED: the four are ground units and a
+// FLY action's route is a FLY route]. A swapped unit becomes a random enemylist enemy (the act2 `_2` versions) at the
+// replaced unit's time and route, worth DUCK_COINS to its killer (bounty, also in 联防). A pair boss field has one spawn
+// list that its two players' handlers edit in turn; each player's 0–2 come from the enemies whose route ends on that
+// player's half (`ev.side` + `ev.routes`, the half rule of the field's bounties, server/match/waves.js routeByMotion), the
+// share taken over that half [ASSUMED: "你和队友遭遇的敌人" — the enemies heading for the player's own protection point;
+// each official client simulates its own battle, docs/research/08 appendix A]. The originals never exist, so none of
+// their death / kill / leak effects happen. Reaching the protection point costs 1 LP ("但进入保护目标点将减少1点目标生命值":
+// the enemies' data lpr, tools/build-data.mjs).
 
 export const DUCK_BAND = 'band_ducklord';
 /** "击倒这些敌人者获得1资金奖励" (the blackboard's `count` is 1 too). */
 export const DUCK_COINS = 1;
 /** Battle kinds the swap applies to (PRTS: the Final Assault and the Hidden Core too). */
 const DUCK_KINDS = new Set(['normal', 'boss', 'hidden']);
+/** Boss-field column between the left ('L') and the right ('R') player's half (the goals are at cols 2–3 / 17). */
+const BOSS_MID_COL = (GEO.BOSS_RECT.c0 + GEO.BOSS_RECT.c1) / 2;
 
 function duckParams() {
   for (const b of buffsOf(bandRecord(DUCK_BAND))) if (b.key === 'round_start_all_player_change_enemy_2') return b.p;
   return null;
 }
 
-/** Rewrite `spawns` in place (exported for tests). Returns the replaced spawn specs. */
-export function duckReplace(ctx, spawns, p, ownerPlayerId) {
+/**
+ * Rewrite `spawns` in place (exported for tests). Returns the replaced spawn specs. `side` ('L' | 'R', a pair boss
+ * field) limits the swap to the spawns whose route (`routes[routeIndex]`) ends on that half of the field.
+ */
+export function duckReplace(ctx, spawns, p, ownerPlayerId, { routes = null, side = null } = {}) {
   const gd = ctx.gd;
   const ducks = list(p.enemylist).filter((k) => gd.enemy(k));
   if (!ducks.length || !Array.isArray(spawns)) return [];
   const lo = Math.max(0, int(p.min, 0)), hi = Math.max(lo, int(p.max, lo));
   const want = lo + ctx.rng.int(hi - lo + 1);
   if (want <= 0) return [];
-  // one entry per enemy (split multi-count specs), in spawn-time order
+  const half = side === 'L' || side === 'R';
+  const onHalf = (s) => {
+    if (!half) return true;
+    const r = Array.isArray(routes) ? routes[s.routeIndex] : null;
+    const c = r && Array.isArray(r.end) ? Number(r.end[1]) : NaN;
+    return side === 'R' ? c > BOSS_MID_COL : c < BOSS_MID_COL;
+  };
+  // one entry per enemy of the player (split multi-count specs), in spawn-time order
   const flat = [];
   for (let i = 0; i < spawns.length; i++) {
     const s = spawns[i];
+    if (!s || !onHalf(s)) continue;
     const cnt = Math.max(1, int(s.count, 1));
     for (let k = 0; k < cnt; k++) flat.push({ i, k, t: num(s.time, 0) + k * num(s.interval, 0) });
   }
@@ -439,7 +460,7 @@ const duckGlobal = {
     if (!p || ctx.round < int(p.round, 1)) return;
     const held = ctx.bandId() === DUCK_BAND || ctx.teammates().some((t) => t.bandId() === DUCK_BAND);
     if (!held) return;
-    duckReplace(ctx, ev.spawns, p, ctx.playerId);
+    duckReplace(ctx, ev.spawns, p, ctx.playerId, { routes: ev.routes, side: ev.side });
   },
 };