diff --git a/apps/shaders_lab/shaders_lab.exe b/apps/shaders_lab/shaders_lab.exe
index 4b02245d..dbf0fa62 100755
Binary files a/apps/shaders_lab/shaders_lab.exe and b/apps/shaders_lab/shaders_lab.exe differ
diff --git a/cpp/functions/gfx/dag_catalog.cpp b/cpp/functions/gfx/dag_catalog.cpp
index d687ae66..6ece0091 100644
--- a/cpp/functions/gfx/dag_catalog.cpp
+++ b/cpp/functions/gfx/dag_catalog.cpp
@@ -257,3 +257,78 @@ const DagNodeDef* dag_find(const std::string& name) {
 }
 
 } // namespace fn::gfx
+
+#ifdef DAG_CATALOG_TEST
+#include <cassert>
+#include <cstdio>
+#include <set>
+
+int main() {
+    using namespace fn::gfx;
+    const auto& cat = dag_catalog();
+
+    // 1. Catalog not empty
+    assert(!cat.empty());
+
+    // 2. All node names are unique
+    std::set<std::string> names;
+    for (const auto& n : cat) {
+        assert(names.insert(n.name).second && "duplicate node name");
+    }
+
+    // 3. Invariants by kind
+    int gen_count = 0, op_count = 0, blend_count = 0, output_count = 0;
+    for (const auto& n : cat) {
+        switch (n.kind) {
+            case DagKind::Gen:
+                assert(n.num_inputs == 0 && "Gen must have 0 inputs");
+                ++gen_count; break;
+            case DagKind::Op:
+                assert(n.num_inputs >= 1 && "Op must have >= 1 input");
+                ++op_count; break;
+            case DagKind::Blend:
+                assert(n.num_inputs >= 2 && "Blend must have >= 2 inputs");
+                ++blend_count; break;
+            case DagKind::Output:
+                assert(n.num_inputs == 1 && "Output must have exactly 1 input");
+                ++output_count; break;
+        }
+        assert(n.num_inputs >= 0 && n.num_inputs <= 4);
+        assert(n.body_glsl && "body_glsl must be set");
+    }
+
+    // 4. Exactly one Output in the catalog
+    assert(output_count == 1 && "catalog must declare exactly one Output node");
+
+    // 5. At least one Gen and one Op
+    assert(gen_count >= 1);
+    assert(op_count >= 1);
+    assert(blend_count >= 1);
+
+    // 6. dag_find works and returns nullptr for unknown names
+    assert(dag_find("output") != nullptr);
+    assert(dag_find("plasma") != nullptr);
+    assert(dag_find("__nonexistent__") == nullptr);
+
+    // 7. Every non-Output body emits non-empty GLSL
+    for (const auto& n : cat) {
+        if (n.kind == DagKind::Output) continue;
+        auto body = n.body_glsl(0);
+        assert(!body.empty() && "non-Output nodes must emit body");
+        // sanity: should contain a return statement
+        assert(body.find("return") != std::string::npos);
+    }
+
+    // 8. Control param indices stay within 0..3
+    for (const auto& n : cat) {
+        for (const auto& c : n.controls) {
+            for (int idx : c.param_idx) {
+                assert(idx >= -1 && idx < 4);
+            }
+        }
+    }
+
+    std::printf("dag_catalog: 8/8 asserts passed (%zu nodes)\n", cat.size());
+    return 0;
+}
+#endif
diff --git a/cpp/functions/gfx/dag_compile.cpp b/cpp/functions/gfx/dag_compile.cpp
index 591d7189..09ecf122 100644
--- a/cpp/functions/gfx/dag_compile.cpp
+++ b/cpp/functions/gfx/dag_compile.cpp
@@ -106,3 +106,83 @@ std::string compile_dag_to_glsl(const std::vector<DagStep>& pipeline) {
 }
 
 } // namespace fn::gfx
+
+#ifdef DAG_COMPILE_TEST
+#include <cassert>
+#include <cstdio>
+
+static bool contains(const std::string& hay, const std::string& needle) {
+    return hay.find(needle) != std::string::npos;
+}
+
+int main() {
+    using namespace fn::gfx;
+
+    // 1. Empty pipeline → seed color
+    {
+        std::vector<DagStep> p;
+        auto s = compile_dag_to_glsl(p);
+        assert(contains(s, "fragColor = vec4(0.04"));
+    }
+
+    // 2. Single Gen → fragColor = out_0
+    {
+        std::vector<DagStep> p;
+        DagStep g; g.id = "a"; g.name = "plasma";
+        p.push_back(g);
+        auto s = compile_dag_to_glsl(p);
+        assert(contains(s, "vec4 node_0"));
+        assert(contains(s, "vec4 out_0 = node_0("));
+        assert(contains(s, "fragColor = out_0"));
+    }
+
+    // 3. Gen + Op → Op uses out_0 as input a
+    {
+        std::vector<DagStep> p;
+        DagStep g; g.id = "a"; g.name = "plasma"; p.push_back(g);
+        DagStep o; o.id = "b"; o.name = "invert"; o.source_ids[0] = "a"; p.push_back(o);
+        auto s = compile_dag_to_glsl(p);
+        assert(contains(s, "out_1 = node_1(out_0, uv)"));
+        assert(contains(s, "fragColor = out_1"));
+    }
+
+    // 4. Blend with multi-source → both inputs resolved
+    {
+        std::vector<DagStep> p;
+        DagStep a; a.id = "a"; a.name = "plasma"; p.push_back(a);
+        DagStep b; b.id = "b"; b.name = "solid";  p.push_back(b);
+        DagStep m; m.id = "m"; m.name = "blend_mix";
+        m.source_ids[0] = "a"; m.source_ids[1] = "b";
+        p.push_back(m);
+        auto s = compile_dag_to_glsl(p);
+        assert(contains(s, "out_2 = node_2(out_0, out_1, uv)"));
+    }
+
+    // 5. Output node drives fragColor from its source, not from last index
+    {
+        std::vector<DagStep> p;
+        DagStep g1; g1.id = "g1"; g1.name = "plasma"; p.push_back(g1);
+        DagStep g2; g2.id = "g2"; g2.name = "solid";  p.push_back(g2);
+        DagStep o;  o.id  = "o";  o.name  = "output";
+        o.source_ids[0] = "g1";  // connect Output to the plasma (first gen), not last
+        p.push_back(o);
+        auto s = compile_dag_to_glsl(p);
+        // Output must NOT emit a node_2 function
+        assert(!contains(s, "vec4 node_2("));
+        // fragColor must come from out_0 (plasma), not out_1 (solid)
+        assert(contains(s, "fragColor = out_0"));
+    }
+
+    // 6. Output with no connection → seed fallback
+    {
+        std::vector<DagStep> p;
+        DagStep g; g.id = "g"; g.name = "plasma"; p.push_back(g);
+        DagStep o; o.id = "o"; o.name = "output"; p.push_back(o); // no source
+        auto s = compile_dag_to_glsl(p);
+        assert(contains(s, "fragColor = vec4(0.04"));
+    }
+
+    std::printf("dag_compile: 6/6 asserts passed\n");
+    return 0;
+}
+#endif
diff --git a/cpp/functions/gfx/dag_node_editor.cpp b/cpp/functions/gfx/dag_node_editor.cpp
index 4419bbc4..2685d02b 100644
--- a/cpp/functions/gfx/dag_node_editor.cpp
+++ b/cpp/functions/gfx/dag_node_editor.cpp
@@ -138,25 +138,26 @@ bool dag_node_editor(std::vector<DagStep>& pipeline) {
         s_ctx = ed::CreateEditor(&cfg);
     }
 
-    // Palette drop zone: accept dropped node types (from the Functions panel)
-    // and queue an add at the mouse canvas position (resolved after ed::Begin).
+    // Palette drop: detect without a capturing target (an InvisibleButton would
+    // steal clicks from the node editor). Observe the active drag-drop payload
+    // and, if the mouse is over this window and the user releases LMB, queue an
+    // add at that canvas position.
     static std::string s_pending_add_name;
     static ImVec2      s_pending_add_pos(0, 0);
     static bool        s_pending_add = false;
 
-    ImVec2 origin = ImGui::GetCursorScreenPos();
-    ImVec2 avail  = ImGui::GetContentRegionAvail();
-    ImGui::InvisibleButton("##dag_drop_zone", avail,
-                           ImGuiButtonFlags_MouseButtonLeft | ImGuiButtonFlags_MouseButtonRight);
-    if (ImGui::BeginDragDropTarget()) {
-        if (const ImGuiPayload* p = ImGui::AcceptDragDropPayload("DAG_NODE_TYPE")) {
-            s_pending_add_name.assign(static_cast<const char*>(p->Data), static_cast<size_t>(p->DataSize));
-            s_pending_add_pos = ImGui::GetMousePos();
-            s_pending_add = true;
+    const bool window_hovered = ImGui::IsWindowHovered(
+        ImGuiHoveredFlags_ChildWindows | ImGuiHoveredFlags_AllowWhenBlockedByActiveItem);
+    if (window_hovered) {
+        if (const ImGuiPayload* p = ImGui::GetDragDropPayload()) {
+            if (p->IsDataType("DAG_NODE_TYPE") && ImGui::IsMouseReleased(ImGuiMouseButton_Left)) {
+                s_pending_add_name.assign(static_cast<const char*>(p->Data),
+                                          static_cast<size_t>(p->DataSize));
+                s_pending_add_pos = ImGui::GetMousePos();
+                s_pending_add = true;
+            }
         }
-        ImGui::EndDragDropTarget();
     }
-    ImGui::SetCursorScreenPos(origin);
 
     ed::SetCurrentEditor(s_ctx);
     ed::Begin("dag_editor", ImVec2(0.0f, 0.0f));