paper(1H): reflect D8 single-op cost model in §2/§3.4 + figure/diagram regen

Two strands bundled as the 1H-codesign-paper refresh unit:

(A) This session — single-op cost-model reflection (depends on 2d8271c):
  - §2 Table 2 (tab:hw): split "FIXED per command" into "FIXED per
    single-op command" (8 cycles) and "FIXED per composite command"
    (40 cycles); §2 dispatch-overhead prose updated to the two-class split.
  - §3.4 (sec:gemm-vs-async): rename paragraph headers + prose to
    async-full / async-tiled; "atomic" -> "single-op" throughout; reframe
    mechanism #3 from the old DMA-only fast-path to the single-op
    fast-path. Headline narrative now: even with EVERY single-op cmd
    (96 DMA + 48 dot + 47 add) charged the light 8-cycle FIXED, composite
    still wins ~2.8x at K=3072 purely on command-count structure (1 vs
    192 commands) -- down from the pre-D8 ~6.3x, and explicitly NOT a
    modelling artifact. Numbers refreshed from the regenerated sweep:
    async-full 3.83->3.91, async-tiled 1.14->~2.53, under-tile corner
    1.06->1.21, depth-2 vs depth-inf spread <1%. New figure wired in.
  - build/main.pdf rebuilt (tectonic); pdftotext-verified (no broken
    refs; Table 2 split, single-op terms, 2.8x/2.53/192-host-commands
    all present).

(B) Prior-session paper work riding along uncommitted: §4 all-reduce
    deep-edit, §5 GQA, §6 discussion trims; milestone_1h_ccl.py plot
    label "FSIM" -> "H2 2025 SW queue baseline"; regenerated diagrams
    under docs/diagrams/** and gemm output PNGs under
    1H_milestone_output/gemm/. (Composite-window gemm plots are
    unaffected by D8 — D8 only changes single-op dispatch FIXED, which
    the composite window excludes.)

All TODO items for the D8 single-op extension are now complete and
pushed across 3 commits (2d8271c cost-model+ADR+tests, 821bbf2 bench
harness, this paper refresh). Full regression green (826 passed, 1
skipped). No remaining work.

NOTE for review (carried from 2d8271c): ADR-0065's "2x CPU-offload win"
headline for GQA decode opt2 may want a refresh to the post-D8 ~1.87x.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/report/1H-codesign-paper/sections/02-platform.tex

@@ -243,14 +243,18 @@ serializing the command descriptor into the scheduler queue. This
 \SI{2}{\nano\second} / \SI{1}{\nano\second} \textsf{PE\_CPU} /
 \textsf{PE\_SCHED} fixed costs: the latter are per-component
 traversal overheads each command pays when it transits those nodes,
-whereas the 40-cycle \textsf{FIXED} term is the command-descriptor
-issue cost. The
-default anchoring (\textsf{FIXED} $= 40$ cycles, $R = 0.0625$
-cycles/byte, i.e.\ \SI{16}{\byte\per\cycle}, at \SI{1}{\giga\hertz})
-places a typical composite at roughly \SI{43}{\nano\second}, and a
-hard cap on a composite's descriptor size prevents the model from
-rewarding arbitrarily large fused commands beyond what real descriptor
-queues accept. In the configurations measured here, command issue is
+whereas the \textsf{FIXED} term here is the command-descriptor
+issue cost. \textsf{FIXED} depends on the command class: a single-op
+command --- one engine operation, i.e.\ a single DMA descriptor, GEMM,
+or elementwise issue --- carries a lighter 8-cycle \textsf{FIXED},
+while the composite command, which the scheduler expands into a
+multi-stage tile-feeder plan, carries 40 cycles
+(\S\ref{sec:gemm-vs-async}). With the composite \textsf{FIXED} $= 40$
+cycles and $R = 0.0625$ cycles/byte (i.e.\ \SI{16}{\byte\per\cycle},
+at \SI{1}{\giga\hertz}) a typical composite lands at roughly
+\SI{43}{\nano\second}, and a hard cap on a composite's descriptor size
+prevents the model from rewarding arbitrarily large fused commands
+beyond what real descriptor queues accept. In the configurations measured here, command issue is
 not the bottleneck---data movement is---so this term stays small
 relative to DMA and collective time.
 
@@ -452,7 +456,8 @@ Inter-CUBE (UCIe PHY) & \SI{512}{\giga\byte\per\second}, \SI{8}{\nano\second}, X
 Inter-SIP (PCIe) & \SI{768}{\giga\byte\per\second} per endpoint \\
 \midrule
 \multicolumn{2}{@{}l}{\emph{Command-issue cost model (defaults)}} \\
-FIXED per command & 40 cycles \\
+FIXED per single-op command & 8 cycles \\
+FIXED per composite command & 40 cycles \\
 per-byte rate $R$ & 0.0625 cycles/byte (\SI{16}{\byte\per\cycle}) \\
 composite size cap & \SI{1024}{\byte} \\
 \bottomrule