Update docs: capped auto-fraction, adaptive steps in roadmap

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: vipenzo

dev-docs/Roadmap.md

@@ -629,6 +629,13 @@ The core turtle system, generative operations, boolean operations, anchor/naviga
 
 ---
 
+## Pending Improvements
+
+### Adaptive loft step density for shape-fn transitions
+The `capped` shape-fn concentrates shape changes in narrow transition zones (fraction of the path). With uniform loft steps, only 2-3 rings may fall in the cap zone, producing coarse faceting. Implement non-uniform `t` sampling: `capped` declares transition zones via shape-fn metadata, and the loft generates denser rings in those zones. Similar to the existing `walk-path-poses-adaptive` (curvature-based density for bloft), but driven by shape-fn change rate rather than path curvature.
+
+---
+
 ## Enhancement Ideas
 
 ### 3D Lattice Structures (implicit surface / marching cubes)

dev-docs/Spec.md

@@ -717,9 +717,11 @@ operations (extrude, loft, revolve) correctly handle shapes with holes.
 (loft (capped shape radius :mode :chamfer) path)       ; Chamfer both caps (linear)
 (loft (capped shape radius :start false) path)         ; Fillet end cap only
 (loft (capped shape radius :end false) path)           ; Fillet start cap only
-(loft (capped shape radius :fraction 0.15) path)       ; Wider transition zone (default 0.08)
+(loft (capped shape radius :fraction 0.15) path)       ; Override auto-fraction
 ```
 
+The transition `fraction` is auto-calculated as `radius / path-length` (geometrically correct fillet). Override with `:fraction` if needed. Radius is clamped to the shape's inradius to prevent degenerate geometry.
+
 **Examples:**
 
 ```clojure
@@ -734,7 +736,7 @@ operations (extrude, loft, revolve) correctly handle shapes with holes.
 - `fillet-shape` / `chamfer-shape` operate on 2D corners (edges along extrusion direction)
 - `capped` operates on 3D cap edges (where profile meets top/bottom face)
 - Both compose freely with all shape-fns and with each other
-- Distance must be less than half the shortest adjacent edge to avoid overlapping cuts
+- Cap transition uses centroid scaling — shape proportions (including fillet radii) are preserved
 - Works on any shape including shapes with holes
 
 **Pattern tiling:**