wip(assembler): round L36 -- tunnel floor without washboard; FI mouth without shards (evaluator v23)

The walk tread was built per segment as a one-sided density clamp, so its crossing with the native
field moved at segment joins (L35: 2.25-2.48 cm washboard). Treads now overlap up to 2 m as bounded
signed-distance slabs (0.06 cm residual). The FI mouth's crater detail and tread met without a smooth
join; v23 filters the local field, drops thin isolated solids and smooth-unions the tread with the
terrain. New floor ripple and mouth fragment/crease audits with L35 as failing controls. 24/24
passage rows, 30/30 determinism, 16/16 invariants, LOD0-8 rings; cost within noise.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

ARCHITECTURE.md

@@ -2138,6 +2138,30 @@ turn. Passage, capsule, support, open-air, bridge, binding, strict layout, captu
 and cost evidence are recorded in
 [`Standalone/Research/WorldAssemblerM3/Linux35/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux35/REPORT.md).
 
+### 8.49 Walk-floor washboard and FI mouth naturalness — World Assembler M3 L36
+
+L35's exported owner-SW mid-tunnel floor measured a 7.250 m repeat at 0.02252 m amplitude; its
+upper-SW fixture arrival measured a 1.438 m repeat at 0.02482 m. Both came from segment-built,
+one-sided support treads meeting the native terrain zero crossing at per-segment joins. The floor
+probe samples the exported walk mesh along the resolved route, separately from the wall-radius scan.
+Eligible tread sections overlap by up to 2 m and all sparse route segments now use a bounded
+signed-distance slab, including SurfaceWorld-to-TunnelNetwork routes. This keeps the tread top stable
+across segment joins while capsule-clearance and native-solid gates retain walkability and open air.
+Regular tread tops remain seated 5 cm lower and ease back to 0.20 m within 20 m of a lower landing;
+seeded shoulder grain is removed, and gravity-facing relief is reduced while side-wall and ceiling
+relief remain irregular.
+
+On v23, the same mesh probes measure 7.188 m / 0.00067 m (0.067 cm) on owner-SW and 6.500 m /
+0.00057 m (0.057 cm) on the upper fixture. The density audit checks five 32 m walk-floor windows at
+0.125 m spacing, rejects amplitudes of 0.015 m or more, and detects its beaded control. The FI mouth
+uses a local 2 m symmetric signed-field filter with the route protected and joins route-mouth support
+to native terrain with a 1.5 m smooth signed-distance union. Its mesh audit reduces the L35
+42.27° fade-ring jump to 27.13° and finds no detached component above the 0.0001 m² area floor; one
+8-triangle subthreshold component at 0.0000266 m² is recorded. The evaluator is version 23. Full
+recipe/style audits, route support, open-air, strict layout, legacy validators, determinism, capture and
+paired-cost results are in
+[`Standalone/Research/WorldAssemblerM3/Linux36/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux36/REPORT.md).
+
 ## 9. Multiplayer model (listen-server first, dedicated-friendly)
 
 > **Status: transport is DESIGN ONLY — nothing is networked in-tree yet** (no `Replicated`/`HasAuthority`/RPCs; a