gqa: ADR-0060/0062/0063/0064 unified GQA kernels + CPU cost model

Land the new GQA fused-attention kernels (ADR-0060) for prefill/decode
across long and short context, the TL discipline primitives they depend
on (ADR-0062 lazy load, ADR-0063 scratch_scope + copy_to), and the
per-op-type CPU issue cost model (ADR-0064). Remove the pre-ADR-0060
mesh-attention baseline now that the unified kernels supersede it.

ADR-0060 (long context)
- _gqa_decode.py: M-fold + 2-level chain reduce-to-root (Level-2
  intra-CUBE row-then-col + Level-1 inter-CUBE) — root-only output.
- _gqa_prefill.py: head-parallel + Ring KV rotation around C CUBEs,
  online-softmax merge per ring step, per-CUBE distributed output.
- Each merge stage wraps in scratch_scope() and persists running
  (m, l, O) via copy_to() to lift the 1 MiB scratch ceiling.

ADR-0060 §B.split.2 (short context, kv_per_cube in {1,2,4,8})
- _gqa_decode_short.py / _gqa_prefill_short.py: no cube-SP; each CUBE
  owns whole KV heads; PE-parallel heads with intra-group chain
  reduce. Prefill has no Ring KV (each head fully resident).

ADR-0062 (lazy tl.load): future-bearing TensorHandle, auto-wait at
first consuming op (dot/MATH/store/send/copy_to/composite).

ADR-0063 (tl.scratch_scope + tl.copy_to): scoped per-tile arena with
copy_to writeback primitive for persistent running state.

ADR-0064 (CPU issue cost model)
- common/cpu_issue_cost.py: per-op-type table (composite=40 ns,
  primitives=5 ns); ratios are load-bearing per D1.
- TLContext: issue_cost_table param; _emit_dispatch_overhead(kind)
  consults table with dispatch_cycles fallback (ADR-0046 §D6
  back-compat).
- Live PE_CPU paths (greenlet + legacy) construct TLContext with
  DEFAULT_CPU_ISSUE_COST so saturation lever (ADR-0060 §1) is
  measurable end-to-end.

P7 headline bench: milestone-gqa-headline writes per-panel
op_log_summary to 1H_milestone_output/gqa_headline/sweep.json. No
figure renderers yet (deferred).

Removals (pre-ADR-0060 baseline now superseded):
- benches: _attention_mesh_kv.py, _attention_mesh_mlo.py,
  _attention_mesh_mlo_2d.py, milestone_gqa_llama70b.py
- tests: test_attention_*, test_mesh_*, test_milestone_gqa_llama70b
- topology: llama70b_4sip.yaml (only consumer was the deleted diag)
- artifacts: 1H_milestone_output/gqa/ (sweep.json + 5 PNGs)
- tests/gqa/ plot helper + test (broken on Windows Tcl/Tkinter)
- ADR-0060/0061 references to deleted file paths cleaned up
  (EN + KO kept in sync).

Tests: 124/124 focused regression green (attention + Phase E + TL
discipline + triton_emu + pe_components). Full regression: 764 pass,
2 pre-existing test_bench_registry failures (stale EXPECTED_NAMES
across multiple benches, not introduced here).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/kernbench/common/pe_commands.py

@@ -73,6 +73,12 @@ class TensorHandle:
     data: object = None              # reserved for validate mode
     space: str = "tcm"               # MemoryStore space ("tcm" | "hbm" | "sram")
     pinned: bool = False             # operand already DMA-staged in TCM (via tl.load)
+    # ADR-0062 §D2: lazy tl.load attaches a LoadFuture here. None for
+    # handles that have no in-flight DMA (constants, math outputs, etc.).
+    # Consumer ops call _await_pending() to yield on the future before
+    # emitting their own command. Excluded from eq/hash/repr so handle
+    # identity is unaffected by pending state.
+    pending: object = field(default=None, compare=False, hash=False, repr=False)
 
 
 @dataclass(frozen=True)
@@ -140,6 +146,22 @@ class MathCmd:
     data_op: bool = True
 
 
+@dataclass(frozen=True)
+class CopyCmd:
+    """TCM-to-TCM byte copy (ADR-0063 §D3.1).
+
+    Emitted by ``tl.copy_to`` to persist a scoped result's bytes to an
+    outside-``scratch_scope`` (persistent) address — the two-arena
+    pattern for tiled flash attention. Runs on the vector engine;
+    op_log classifies as ``op_kind="math"``, ``op_name="copy"``.
+    """
+
+    src: TensorHandle
+    dst: TensorHandle
+    nbytes: int
+    data_op: bool = True
+
+
 @dataclass(frozen=True)
 class CompositeCmd:
     """Composite command: tiled pipeline of DMA_READ + COMPUTE + DMA_WRITE.
@@ -178,7 +200,7 @@ class PeCpuOverheadCmd:
 
 # Union type for all PE commands
 PeCommand = (
-    DmaReadCmd | DmaWriteCmd | GemmCmd | MathCmd
+    DmaReadCmd | DmaWriteCmd | GemmCmd | MathCmd | CopyCmd
     | CompositeCmd | WaitCmd | PeCpuOverheadCmd
 )