feedback5 CB5: in a boss round's prep a watcher sees the boss field — the scouted player's half (mirrored on the right) with the leader standing at its spawn — instead of the normal board without a boss (community report of 2026-10-06, item 55)

Reproduced in the browser (notes i55-repro, an eliminated guest at the boss round): in the Final Assault fight
the watched boss field shows the leader (enemy_9013_acstmk at 10,3), but in the boss round's prep the
eliminated player saw its own empty normal board (camera 'prep', no leader), and a scout of a teammate was the
normal board too, while the players prepare on their half of the boss field with the leader standing there.
Match.prepFieldMeta: in a boss round's prep the scout is built on the boss field (kind 'boss', BOSS_RECT,
units through finalAssault.js bossFieldPlacement: rows − 7, the right half mirrored with RIGHT ↔ LEFT, the player's side;
nextEnemies keeps the leader's spawn tile); game.js frames it with the boss-field prep camera of that side,
which shows the leader (render/app.js leaderShown). With item 56 an eliminated viewer gets it at the round
start without a tap. After the fix the same run: guest field kind 'boss', camera bossPrep, leader shown.

Golden unchanged. Tests: test/match/feedback5-boss-prep-scout.test.js (new, 2). Docs: design/network.md,
design/client.md (§15).

docs/design/client.md

@@ -72,6 +72,6 @@ Target: a **real 3D board layer** rendered with three.js (vendored ESM, no CDN)
 - One camera model drives both layers: `public/js/render/projection.js` keeps its public API (`worldToScreen`, `screenToWorld`/tile picking, presets, transitions) but derives it from a three.js `PerspectiveCamera` initialised from the official configBlackBoard framing, so Spine units, FX, drag/drop and hit-testing stay aligned with the 3D board.
 - Must degrade gracefully: when local-client art or WebGL2 features are missing, fall back to the current 2D atlas board; keep 60 fps (static geometry merged into few draw calls; textures mipmapped; DPR-aware).
 - Implemented (`public/js/render/board3d/*`, `render/app.js`): three.js is downloaded only when the local-art manifest lists the board atlas; the built 3D area, the drawn 2D rows and the lit rect follow `viewKind(kind, {rect})` (the field the camera actually shows: a 'prep' camera on rows ≤ 6 = `bossPrep`); the background plane is extended with mirrored copies and the clear colour matches the fog (no visible edge at any aspect); battle crates live in their own group (survive scene rebuilds) and follow the board mode (`switchableBox`: 3D mesh ⇄ 2D box on a mode switch or a lost WebGL context); quality 'low' drops shadows; `?board=2d|3d` overrides. The direction wheel's range stripes sit between the board canvas and the unit canvas.
-- Done: Final Assault / Hidden Core prep takes place on your own half of the boss field (research 09 §1.2): pieces shown at boss-field positions (row − 7; right-hand player mirrored col → 20 − col, RIGHT ↔ LEFT), drop targets and wheel directions mapped back to board coordinates (`prepCamera` → `bossPrep` in public/js/ui/gameLogic.js; covered by the playtest2 browser tests).
+- Done: Final Assault / Hidden Core prep takes place on your own half of the boss field (research 09 §1.2): pieces shown at boss-field positions (row − 7; right-hand player mirrored col → 20 − col, RIGHT ↔ LEFT), drop targets and wheel directions mapped back to board coordinates (`prepCamera` → `bossPrep` in public/js/ui/gameLogic.js; covered by the playtest2 browser tests). A scout of such a board (`m.field` prep of a boss round) comes in boss-field coordinates with the player's `side` and is framed the same way, the leader standing at its spawn (0.2.0, community report item 55).
 
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