Cause: raidTile took any standable tile of the battle rect; BOSS_RECT holds rows 0-1 (tile_achand, buildable high
ground) and UNITE_RECT both halves of the 联防 map. Battle.onOwnBoard(ps, r, c) maps the board region (rows 9-12,
cols 2-10) onto the field as mapTile maps the pieces; raidTile takes only those tiles.
Golden: 8 scenarios, each with members that landed on the partner's half on the parent (checked instrumented):
fields boss-boss_2/3/4/5/6-pair, hidden-boss_8/10-pair; matches coop2-ABYSS-10-boosted (ai_0 on the right half).
Tests: test/sim/feedback5-raid-own-board.test.js (4, fail on the parent). Docs: DESIGN §25.18.1, docs/SIM.md.