Snapshot: fog implementation + fidelity tooling baseline (pre bilinear-clamp fix)

Per-vertex GS fog end-to-end (gs_stub emit incl. persp_emit5, gs_prim_list_feeder
XYZ2->XYZF2 on PRIM.FGE, gs_make_sh3_scheduler_fixture.py F/FGE packing), new fog
TBs, fidelity attribution tooling. Functional baseline before removing the dead
bilinear lerp8 clamps (Codex: 161-node comb loop -> -0.042ns setup fail).

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

docs/ch373_audit_log.md

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+# Ch373 Audit Log - Earlier-Capture Eight-Draw Expansion
+
+## Fixture
+
+- `zsrte8` groups eight chronological authentic draws from capture `20260624224047` into three
+  runtime-CLUT epochs: 204, 204, and 90 triangles.
+- Epoch 0 performs the texture fill; epochs 1 and 2 perform CRC-verified resident reuse at CBP `508`.
+- Native geometry is bounded by x `63..443`, y `40..471`. The feeder lists are 1,843, 1,843, and 817 words.
+
+## Integration Gate
+
+- Depth-4096 integration and independent trace runs both pass with 520,733 accepted fragments,
+  429,471 persistent-Z updates, three fresh drains, and zero drops.
+- The exact scoreboards report Z `0/307200` and color `0/128277` mismatches.
+- Request-FIFO high-water is bounded at 2,090, 940, and 1,757 requests across the three epochs,
+  below the production depth of 4,096.
+
+## Silicon Closure
+
+- The DE25 completed one texture fill, two CRC-verified resident reuses, all 498 expected draw records, and
+  zero fragment drops. Its framebuffer reports 128,277 nonzero pixels in bounds `(65,41)..(443,470)`.
+- Board and integration framebuffers are byte-identical at SHA-256
+  `3a2395cc0d4829560016aeac852b029ba46248ee1dcae3d74d541a64688b2a32`.
+- The complete 520,733-fragment trace independently replays to the board framebuffer exactly:
+  429,471 Z-pass updates, 128,277 covered pixels, zero uncovered writes, and `307200/307200` exact colors.
+
+## Result
+
+Ch373 closes the earlier-capture eight-draw expansion on silicon with no RTL, constraint, or fit change.