Hypershade-style pin display modes for material graph nodes

Each node gets an All/Conn toggle: connected-only mode hides
unconnected pins behind collapsed connector nubs on the title row;
dragging a link onto (or from) a nub opens a menu to pick which hidden
pin to wire, and the pin appears once connected. The toggle is drawn
and hit-tested geometrically, and its tooltip is deferred to after
NE::End() so it lands at the cursor. A new Preferences > Material
checkbox opts into persisting the per-node mode as USD customData
(uiShowAllPins); otherwise it stays session-only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/core/MaterialManager.cpp

@@ -138,6 +138,7 @@ ShaderGraphSnapshot MaterialManager::GetShaderGraph(const pxr::SdfPath& material
     if (!materialPrim.IsValid()) return snapshot;
 
     static const pxr::TfToken kUiPositionKey("uiPosition");
+    static const pxr::TfToken kUiShowAllPinsKey("uiShowAllPins");
 
     // Seed with every shader under the material, recursing into nested node
     // graphs (usdMtlx nests a material's nodes inside UsdShadeNodeGraph
@@ -179,6 +180,10 @@ ShaderGraphSnapshot MaterialManager::GetShaderGraph(const pxr::SdfPath& material
             node.hasAuthoredPosition = true;
         }
 
+        pxr::VtValue showAllValue = child.GetCustomDataByKey(kUiShowAllPinsKey);
+        if (showAllValue.IsHolding<bool>())
+            node.showAllPins = showAllValue.UncheckedGet<bool>();
+
         // Prefer the full Sdr-defined pin set (so unauthored pins can still be
         // dragged to create a connection); fall back to authored attributes
         // only for shader types the registry doesn't know about.

src/core/MaterialManager.h

@@ -48,6 +48,12 @@ struct ShaderGraphNode {
     /// False when no uiPosition custom data is authored (typical for networks
     /// referenced from .mtlx) — the editor auto-lays such nodes out instead.
     bool         hasAuthoredPosition = false;
+    /// Hypershade-style pin display mode, read from customData when the
+    /// "keep graph node view settings in USD" preference authored it; true
+    /// (show every pin) when unauthored. False hides unconnected pins,
+    /// collapsing them into a single connectable "more pins" nub per side
+    /// (see MaterialEditorPanel) until a new connection reveals one by name.
+    bool         showAllPins = true;
     std::vector<ShaderPinInfo> inputs;
     std::vector<ShaderPinInfo> outputs;
 };