Fillets and chamfers along closed chains of curved edges between any two smooth sides (a branch pipe meeting a main pipe): a ball rolled along the edge gives the contact curves and the blend (rational B-spline through exact arcs, smooth across the chain's joints); side faces trimmed to the contacts and seams shortened; merged topology joins free-form faces that meet smoothly by their exact normals

Oracle: 72/76.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

ROADMAP.md

@@ -9,7 +9,7 @@ features → parametric timeline) as an open, pure-Rust, agent-drivable applicat
 |---|---|
 | Where are we? | **M0 done; M1/M2 in progress.** Sketch with solver, extrude (taper, two-sided, through all), revolve, fillet/chamfer, holes, patterns, mirror, shell, draft, loft, sweep, split, construction planes, parameters that rebuild the timeline, STEP/STL export, desktop and browser (wasm) app with Fusion-style selection (hover/selected highlights, origin planes, click-to-pick sketch planes, multi-select, window/crossing box selection, animated view cube), CLI, MCP server, oracle harness. |
 | Command parity (in scope) | **139 / 541 (26%)** in-scope commands; SOLID + SKETCH **102 / 291 (35%)** — [docs/parity.md](docs/parity.md) |
-| Fusion oracle | **70 / 76 parts match** (batch 1: 29/29; batch 2 in progress) — [docs/oracle.md](docs/oracle.md) |
+| Fusion oracle | **72 / 76 parts match** (batch 1: 29/29; batch 2 in progress) — [docs/oracle.md](docs/oracle.md) |
 | Tests | 85 (solver, profiles, kernel booleans/blends/measures, expressions, timeline, file formats, camera, engine end-to-end, hostile-input fuzz over every command) |
 | Gates | `cargo xtask ci`: fmt, clippy -D warnings, tests, asset attribution, layering, wasm32 build — green |
 | Weighted parity estimate | **≈ 5%** of Fusion's Design workspace by importance (sketch + basic solids are the core, but surfaces, assemblies, sheet metal, CAM, drawings are untouched) |
@@ -60,8 +60,10 @@ headline counts in-scope tabs only and lists the deferred ones separately.
   chain), including circles and walls at any angle (boss bases and tops, bores, pocket floors,
   plate outlines), loops with sharp corners between straight edges (the blends meet in mitres),
   rounded corners rounded again (sphere octants, tori at concave corners); every edge of a
-  convex planar body or of an extruded part; fillets inside patterns. Edges between two curved
-  faces are not supported yet.
+  convex planar body or of an extruded part; fillets inside patterns; closed chains of curved
+  edges between any two smooth sides (a branch pipe on a main pipe), by a rolling ball (the
+  blend a rational B-spline through exact arcs). Open chains of curved edges are not supported
+  yet.
 - Booleans: prisms along one direction (plates with holes, slots, patterns of them, equal
   sections stacked end to end) are combined exactly in 2D; bodies touching along one whole face
   (a part and its mirror image) are stitched; coincident planar faces are pushed apart when