feedback6 R21A: a 突袭 member may land on a teammate's half when both halves of the field are taken — the two-helper 联防 field and the Final Assault / Hidden Core pair field (the owner's decision of 2026-10-07): Battle.onFieldBoard (onOwnBoard of any player of the battle) read by raidTile only; a lone 联防 helper's empty half, a solo boss field's other half and the hand / 临时整备区 rows stay closed, every other landing rule kept, 乌尔比安's S3 【移动】 keeps onOwnBoard; golden: 8 moved, each parting from the parent at a member's first landing on its teammate's half (checked tick by tick with the parent instrumented) — fields boss-boss_2 / 3 / 4 / 5 / 6-pair and hidden-boss_8 / 10-pair (the right player's 缄默德克萨斯 / 伊内丝 / 仇白 / 耀骑士临光 on the left player's half, 1–7 landings per battle, the first 0.3–39.8 s in), matches coop4-ABYSS-7 (round 6's two-helper 联防: ai_2's 斯卡蒂 on ai_1's half at 52 s; only ai_1 / ai_2 dmgDealt move, 8263 between them); unite-2 unchanged (its two landings stay on their own half)

Tests: test/sim/feedback5-raid-own-board.test.js — the pair field (the right player's member onto the left telin's board tile (2,3), the left player's onto the mirrored right (2,17), the hand rows closed) and the two-helper 联防 (each helper onto the other's half; 乌尔比安 beside a teammate stays on his own) fail on the parent; the solo boss field's hand rows and the lone helper unchanged.
Docs: docs/history/0.2.1.md (new, §26; §26.1 cites the owner's decision and PRTS 卫戍协议/帮助 §联防阶段), the DESIGN index row and versions line, a pointer from §25.18.1, docs/SIM.md (onFieldBoard; onOwnBoard now 乌尔比安's only).

docs/DESIGN.md

@@ -4,7 +4,7 @@ This is the **single source of truth** for every implementer. Research lives in
 
 Language: player-facing text is **Simplified Chinese** by default, with an English switch since 0.2.0 (§25.2, docs/I18N.md: UI strings through `t('中文')`, game texts from the official Chinese data or the official EN client's). Code, comments and identifiers are English.
 
-Versions: the first public release was **0.1.0** (2026-10-02, the state of §0–§20.15); the releases after it add the player feedback and GitHub reports — 0.1.1 §21, 0.1.2 §22, 0.1.3 §23, 0.1.4 §24 — and **0.2.0** (`package.json`, `shared/constants.js APP_VERSION`; `CHANGELOG.md`) the maintainability refactor, two languages, 补位, 自选编队 and their fidelity work — §25 — and is the state described by this document. The labels v1 / v2 / v2.1–v2.5.2 in §0, §14–§20 and in the BALANCE / SIM comparisons name the design generations and the private playtest builds that came before it; they are kept as history.
+Versions: the first public release was **0.1.0** (2026-10-02, the state of §0–§20.15); the releases after it add the player feedback and GitHub reports — 0.1.1 §21, 0.1.2 §22, 0.1.3 §23, 0.1.4 §24 — and **0.2.0** (2026-10-07; `CHANGELOG.md`) the maintainability refactor, two languages, 补位, 自选编队 and their fidelity work — §25. The 0.2.1 dev line (`package.json`, `shared/constants.js APP_VERSION`: `0.2.1-dev`) adds §26 and is the state described by this document. The labels v1 / v2 / v2.1–v2.5.2 in §0, §14–§20 and in the BALANCE / SIM comparisons name the design generations and the private playtest builds that came before it; they are kept as history.
 
 ---
 
@@ -32,3 +32,4 @@ normative lines it rewrote).
 | §23 | [history/0.1.3.md](history/0.1.3.md) | 0.1.3 — community reports after 0.1.2 |
 | §24 | [history/0.1.4.md](history/0.1.4.md) | 0.1.4 — community reports after 0.1.3 |
 | §25 | [history/0.2.0.md](history/0.2.0.md) | 0.2.0 |
+| §26 | [history/0.2.1.md](history/0.2.1.md) | 0.2.1 — after the 0.2.0 release |