policy(adr): ADR-0026 Revision 6 — document DPPolicy.cube_start

Amends ADR-0026 to reflect the cube_start field added in e2fe331.
The production code shipped without an ADR update; this fills that
gap. Documentation-only change (no production code, no test code).

Changes (mirrored in both EN and KO):
- Status: Revision 5 → Revision 6
- D1: add ``cube_start: int = 0`` to the canonical DPPolicy dataclass
- D3: ``cube = policy.cube_start + cube_id`` in resolve_dp_policy
- D8: new section explaining purpose (disjoint cube sub-meshes for
      GQA Llama-70B 8-KV-group headline), semantics, default-0 backward
      compatibility, intra-device constraint, design rationale
      (scalar vs 2D origin vs cube_ids list), and the kernel-side
      cube_start subtraction needed to compensate for ADR-0022's
      physical-cube-id ``program_id(axis=1)`` semantics.

tools/verify_adr_lang_pairs.py passes (EN/KO Status keyword and
title in sync).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/adr-ko/ADR-0026-par-dppolicy-intra-device.md

@@ -2,7 +2,7 @@
 
 ## Status
 
-Accepted (Revision 5 — Phase 2 landed 2026-04-14, 523 passed + 1 strict xfail)
+Accepted (Revision 6 — cube_start 추가 2026-06-04; Revision 5 landed 2026-04-14)
 
 ## Context
 
@@ -30,9 +30,11 @@ class DPPolicy:
     pe: Literal["replicate", "column_wise", "row_wise"] = "replicate"
     num_pes: int | None = None
     num_cubes: int | None = None
+    cube_start: int = 0   # Revision 6 — SIP 내 첫 cube 인덱스; D8 참조
 ```
 
 제거되는 필드: `sip`, `num_sips`.
+추가되는 필드 (Revision 6): `cube_start` — D8 참조.
 
 ### D2. `ShardSpec` — structural (sip, cube, pe) 좌표, `pe_index` 완전 제거
 
@@ -114,7 +116,7 @@ def resolve_dp_policy(
         for ls in local_shards:
             all_shards.append(ShardSpec(
                 sip=target_sip,                              # from caller (current_device)
-                cube=cube_id,                     # local within SIP
+                cube=policy.cube_start + cube_id,            # Rev 6: D8 cube_start만큼 shift; 기본 0 = local within SIP
                 pe=ls.local_pe,                              # local within cube (explicit name)
                 offset_bytes=cube_offset + ls.offset_bytes,
                 nbytes=ls.nbytes,
@@ -224,6 +226,47 @@ KernBench는 사내 프로젝트로 call site가 한정되어 있어 한 번에
 **Silent drift 차단**이 property 완전 제거의 주된 이점: global flat을 기대한
 코드가 SIP-local 결과를 받아 조용히 잘못된 인덱싱을 할 가능성 제거.
 
+### D8. SIP 내 분리된 cube sub-mesh를 위한 `cube_start: int = 0` 추가
+
+**Revision 6 추가 사항 (2026-06-04)**.
+
+**목적**: 한 SIP 내에서 분리된 cube sub-mesh 지정 (예: 0..7과 8..15을 함께
+사용). GQA Llama-70B 8-KV-group 헤드라인 타겟 — SIP당 2×4 KV-group 2개 ×
+4 SIP = 64 cubes — 의 두 번째 KV-group을 기본값 0..7이 아닌 cubes 8..15에
+배치하기 위해 필요.
+
+**Semantics**: `resolve_dp_policy`가
+`cube = policy.cube_start + cube_id`로 ShardSpec 생성 (cube_id는 launch 내에서
+`0..num_cubes-1` 순회). 선택된 cube는 target SIP 내의
+`[cube_start, cube_start + num_cubes)` 범위.
+
+**기본값**: `cube_start = 0`은 기존 모든 호출 사이트 동작을 bit-for-bit
+보존 (이전처럼 `ShardSpec.cube ∈ [0, num_cubes)`). CCL milestone bench의
+full-SIP `DPPolicy(num_cubes=16)`은 그대로 cubes 0..15 생성.
+
+**제약**: intra-device 불변성 보존.
+`cube_start ∈ [0, cubes_per_sip)`이며
+`cube_start + num_cubes ≤ cubes_per_sip`. SIP 경계 교차는 여전히
+`ahbm.set_device(rank)` (ADR-0024)의 책임.
+
+**왜 scalar인가** (2D `cube_mesh_origin`이나 임의 `cube_ids` list가 아닌):
+consumer 커널 (예: `_attention_mesh_mlo_2d`)이 row-major contiguous cube를
+가정; scalar `cube_start`는 `num_cubes`와 자연스럽게 쌍을 이룸 (범위 =
+`[start, start + count)`); 기본값 0에서 마이그레이션 부담 없음. 비연속
+케이스가 필요해지면 향후 더 일반적인 설계를 위에 얹을 수 있음.
+
+**하위 호환성**: 기본값이 있는 가산적 변경. 기존 호출 사이트의 변경을
+강제하지 않음. D7의 "breaking change" 입장은 원래 sip/num_sips 제거에만
+해당하며, `cube_start`는 기존 호출자를 깨지 않음.
+
+**커널 측 참고**: kernbench의 `tl.program_id(axis=1)`은 launch-local rank가
+아닌 물리 cube id를 반환 (ADR-0022). `program_id(axis=1)`에서 ring 위치를
+도출하는 커널은 `cube_start > 0`일 때 launch-local rank를 복원하기 위해
+`cube_start`를 빼야 함 — 그렇지 않으면 out-of-bounds sub-mesh 위치를
+계산하여 deadlock 발생. 참고 패턴은 `_attention_mesh_mlo_2d.py` 참조.
+ADR-0022의 향후 개정에서 `program_id(axis=1)`을 launch-local rank semantics로
+이동하면 커널 측 명시적 차감이 제거될 수 있음.
+
 ## Dependencies
 
 - **ADR-0024** (launcher): `set_device(rank)` 및 current-device scoping이

docs/adr/ADR-0026-par-dppolicy-intra-device.md

@@ -2,7 +2,7 @@
 
 ## Status
 
-Accepted (Revision 5 — Phase 2 landed 2026-04-14, 523 passed + 1 strict xfail)
+Accepted (Revision 6 — cube_start added 2026-06-04; Revision 5 landed 2026-04-14)
 
 ## Context
 
@@ -31,9 +31,11 @@ class DPPolicy:
     pe: Literal["replicate", "column_wise", "row_wise"] = "replicate"
     num_pes: int | None = None
     num_cubes: int | None = None
+    cube_start: int = 0   # Revision 6 — first cube in SIP; see D8
 ```
 
 Removed fields: `sip`, `num_sips`.
+Added fields (Revision 6): `cube_start` — see D8.
 
 ### D2. `ShardSpec` — structural (sip, cube, pe) coordinates, `pe_index` fully removed
 
@@ -120,7 +122,7 @@ def resolve_dp_policy(
         for ls in local_shards:
             all_shards.append(ShardSpec(
                 sip=target_sip,                              # from caller (current_device)
-                cube=cube_id,                     # local within SIP
+                cube=policy.cube_start + cube_id,            # Rev 6: shifted by D8 cube_start; default 0 = local within SIP
                 pe=ls.local_pe,                              # local within cube (explicit name)
                 offset_bytes=cube_offset + ls.offset_bytes,
                 nbytes=ls.nbytes,
@@ -239,6 +241,53 @@ property: code that expected a global flat could otherwise silently
 receive a SIP-local result and index incorrectly — that possibility is
 eliminated.
 
+### D8. Add `cube_start: int = 0` for disjoint cube sub-meshes within a SIP
+
+**Revision 6 addition (2026-06-04)**.
+
+**Purpose**: address a disjoint cube sub-mesh within one SIP (e.g.
+cubes 8..15 alongside cubes 0..7). Required by the GQA Llama-70B
+8-KV-group headline target — two 2×4 KV-groups per SIP × 4 SIPs = 64
+cubes — where the second KV-group on each SIP must land on cubes 8..15
+instead of the default 0..7.
+
+**Semantics**: `resolve_dp_policy` returns `ShardSpec` with
+`cube = policy.cube_start + cube_id`, where `cube_id` iterates
+`0..num_cubes-1` within the launch. Selected cubes lie in
+`[cube_start, cube_start + num_cubes)` within the target SIP.
+
+**Default**: `cube_start = 0` preserves every existing call site
+bit-for-bit (`ShardSpec.cube ∈ [0, num_cubes)` as before). The CCL
+milestone bench's full-SIP `DPPolicy(num_cubes=16)` continues to
+produce cubes 0..15.
+
+**Constraint**: intra-device invariant preserved.
+`cube_start ∈ [0, cubes_per_sip)` and
+`cube_start + num_cubes ≤ cubes_per_sip`. SIP boundary crossing remains
+the job of `ahbm.set_device(rank)` (ADR-0024).
+
+**Why scalar** (not 2D `cube_mesh_origin` or arbitrary `cube_ids` list):
+consumer kernels (e.g. `_attention_mesh_mlo_2d`) assume row-major
+contiguous cubes; scalar `cube_start` pairs naturally with `num_cubes`
+(range = `[start, start + count)`); zero migration churn at default 0.
+More general designs can be added on top later if a non-contiguous use
+case appears.
+
+**Backward compatibility**: additive change with default value. No
+existing call site is forced to change. The "breaking change" stance
+in D7 applies only to the original sip/num_sips removal — `cube_start`
+does NOT break existing callers.
+
+**Kernel-side note**: kernbench's `tl.program_id(axis=1)` returns the
+physical cube id (ADR-0022), not a launch-local rank. Kernels that
+derive ring positions from `program_id(axis=1)` must subtract
+`cube_start` to recover launch-local rank when `cube_start > 0` —
+otherwise they compute out-of-bounds sub-mesh positions and deadlock.
+See `_attention_mesh_mlo_2d.py` for the reference pattern. A future
+revision of ADR-0022 could move `program_id(axis=1)` to launch-local
+rank semantics; that change would let kernels drop the explicit
+subtraction.
+
 ## Dependencies
 
 - **ADR-0024** (launcher): `set_device(rank)` and current-device scoping