wip(assembler): round L33 -- SurfaceWorld can be an upper strate; FloorProfileBlend measures seams

Route planning for an upper SurfaceWorld failed on long candidate chords over steep relief; chords
are now capped to the arrival/departure radii on an 8 m centre grid with an origin-proximity cost
(21.5 m walk, about 4 deg). The departure passage starts at the SW ground and tunnels down through rock.
FI -> SW -> TN fixture: all 4 styles pass every passage audit on both compilers. FloorProfileBlend
now checks endpoint height/tangent seams (step and tangent-step negative controls detected). Owner
world hashes unchanged; 30/30 determinism; cost within noise.

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

ARCHITECTURE.md

@@ -2076,6 +2076,40 @@ transition one micrometre wider than declared and a band one micrometre below th
 [`Standalone/Research/WorldAssemblerM3/Linux29/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux29/REPORT.md)
 for audit measurements, hashes, timings, captures and run history.
 
+### 8.47 Ground-bound SurfaceWorld departure routes — World Assembler M3 Linux L33
+
+An intra-strate SurfaceWorld route follows the resolved terrain ground profile. Its route-point Z
+is the ground height plus the player's half-height; the route does not descend to the strate's
+bedrock boundary. Bedrock belongs to the separate inter-strate passage, which begins at the
+SurfaceWorld departure mouth on the ground and tunnels outward and down through native rock and
+the boundary into the next strate.
+
+The old fixed candidate envelope used a 64 m chord and 16 m centre spacing. On the L33 upper-SW
+fixture, replaying that envelope sampled ground from −507.767 to −464.857 m; 366/648 candidate paths
+exceeded the 15° grade limit. The worst failures clustered near the outer west/northwest terrain
+shoulder (up to 79.971°) and the steep approach slopes around the origin. Candidate diagnostics
+separate grade failures from endpoints outside the bounded arrival/departure placement disks.
+The bounded search now limits its longest chord to the two mouth radii minus a 3 m clearance
+margin, checks centres every 8 m, and ranks endpoints near the route anchors. It finds a 21.5 m
+route from (−2.75, 0) to (18.75, 0), sampled on ground and accepted by the full capsule/support/
+grade audit.
+
+The SurfaceWorld departure passage starts at the ground mouth with a 1.5 m portal, then smoothsteps
+to a 3.5 m rock tunnel over 9 m. Its ring is sized and oriented outward from the mouth, so the
+approach does not cut back under the walk route. The `FloatingIslands → SurfaceWorld → TunnelNetwork`
+fixture passes all four passage styles, including both interfaces, capsule clearance, support,
+grade, walkability, naturalness, open-air, column ends, long-bridge and route-binding audits.
+
+`FloorProfileBlend` previously compared each curved floor profile with its straight chord and
+applied a 2-voxel limit. That is a curvature measurement, not a seam measurement. It now checks
+endpoint height and tangent continuity at 0.01 voxel and 0.001 voxel/m; the 3-voxel step and
+0.25 voxel/m tangent-step controls are both detected. SurfaceWorld owner hashes remain identical
+to L32 because the route-mouth, expanded column sizing and short-span support changes apply only
+when SurfaceWorld is the upper strate. No evaluator or recipe version changed.
+
+[`Standalone/Research/WorldAssemblerM3/Linux33/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux33/REPORT.md)
+records the four-style audits, captures, determinism, owner hashes, costs and retries.
+
 ## 9. Multiplayer model (listen-server first, dedicated-friendly)
 
 > **Status: transport is DESIGN ONLY — nothing is networked in-tree yet** (no `Replicated`/`HasAuthority`/RPCs; a