fix(feedback): resolve VDE-077 — rename Continuity::C0 to G0, verify PCurve is NurbsCurve alias

- Issue 1 (n_sided_fill PCurve): Verified not reproducible. PCurve is a public
  using-alias (PCurve = curves::NurbsCurve) in vde/brep/trimmed_surface.h.
  Header and implementation both use NurbsCurve consistently.
- Issue 2 (Continuity enums): Renamed Continuity::C0 → G0 to match
  ContinuityLevel::G0 naming. C0 was unused in entire codebase.
  Full unification deferred (architecture-level — ContinuityLevel needs None
  for analysis results while Continuity serves active operations).

feedback/VDE-077.md

@@ -1,52 +1,29 @@
 # VDE-077: n_sided_fill PCurve input + Continuity enum inconsistency
 
 - **Date**: 2026-07-31
-- **Status**: Open
-- **VDE commit**: deaaaf4 (ViewDesign集成)
+- **Status**: Resolved (2026-07-31)
+- **VDE commit**: 630a4a6
 
 ## Issue 1: n_sided_fill takes PCurve instead of NurbsCurve
 
-`vde::curves::n_sided_fill()` in `surface_extension.h` declares boundary curves as
-`std::vector<NurbsCurve>`, but the compiled library actually expects
-`std::vector<vde::brep::PCurve>`.
-
-```cpp
-// Declared in header:
-[[nodiscard]] NurbsSurface n_sided_fill(
-    const std::vector<NurbsCurve>& boundary_curves,
-    Continuity continuity = Continuity::G2);
-
-// Actual compiled signature:
-[[nodiscard]] NurbsSurface n_sided_fill(
-    const std::vector<vde::brep::PCurve>& boundary_curves,
-    Continuity continuity);
-```
-
-**Problem**: `PCurve` is an internal vde::brep type not exposed in public API.
-Users cannot easily convert their NURBS boundary curves to PCurve.
-This blocks the n-sided fill surface functionality.
-
-**Expected**: Accept `std::vector<NurbsCurve>` directly, matching the header declaration.
+**Resolution**: VERIFIED — NOT REPRODUCIBLE.
+`PCurve` is defined as `using PCurve = curves::NurbsCurve;` in `vde/brep/trimmed_surface.h`,
+making it a public type alias. Header (`surface_extension.h`) and implementation
+(`surface_extension.cpp`) both consistently use `std::vector<NurbsCurve>`. Since
+`PCurve` ≡ `NurbsCurve`, the compiled library signature is identical at the ABI level.
+No fix needed.
 
 ## Issue 2: Two separate Continuity enums in same namespace
 
-`vde::curves` defines TWO different continuity enums:
-
-```cpp
-// continuity_types.h
-enum class Continuity { C0, G1, G2, G3 };        // used by extend_surface, n_sided_fill
-enum class ContinuityLevel { None, G0, G1, G2, G3 }; // used by continuity_type, surface_continuity
-```
-
-**Problems**:
-- `Continuity` uses `C0` but `ContinuityLevel` uses `G0` for the same concept
-- Different function families use different enums with no conversion path
-- Confusing to users: `extend_surface()` takes `Continuity` but `surface_continuity()` returns `ContinuityLevel`
-
-**Expected**: Unify into a single enum (e.g., `Continuity` with values `None, C0, G1, G2, G3`),
-or provide implicit conversion between the two.
+**Resolution**: PARTIALLY FIXED.
+- `Continuity::C0` renamed to `Continuity::G0` in `continuity_types.h` (was unused in codebase)
+- Full unification of `Continuity` + `ContinuityLevel` into one enum is deferred (architecture-level change):
+  `ContinuityLevel` serves analysis functions (`continuity_type`, `surface_continuity`)
+  which legitimately need `None` for "no continuity", while `Continuity` serves active
+  operations (`extend_surface`, `n_sided_fill`) where `None` is meaningless.
+  Acknowledged as known design tradeoff.
 
 ## Impact on ViewDesign
 
-- `nSidedFillVde()` is stubbed — cannot use n-sided fill until PCurve issue resolved
-- `extendSurfaceVde()` requires manual Continuity enum mapping (works but ugly)
+- `nSidedFillVde()` can use `NurbsCurve` directly (or `vde::brep::PCurve` — same type)
+- `extendSurfaceVde()` Continuity enum now uses `G0` consistently across both enum types

include/vde/curves/continuity_types.h

@@ -21,7 +21,7 @@ namespace vde::curves {
 /// 几何连续性级别
 /// 用于 curve_tools::connect_curve、surface_extension::extend_surface 等
 enum class Continuity {
-    C0  = 0,  ///< 仅位置连续
+    G0  = 0,  ///< 仅位置连续
     G1  = 1,  ///< 切线/切平面连续
     G2  = 2,  ///< 曲率连续
     G3  = 3,  ///< 挠率/曲率变化率连续