fix(editor): Delete/Backspace key removes selected node + orphan edges

React Flow's built-in keyboard handling was silently no-op'd because
deleteKeyCode wasn't set (v12 defaults it to null when the prop is absent
in the strict TS types we consume). Set it to ['Delete', 'Backspace'] and
add an onNodesDelete handler that filters edges whose endpoints just
vanished — applyNodeChanges only touches nodes, so without this the graph
kept dangling edges.

Also fixes a tsc regression the same touch caught in ConnectionsPage.test
where a request.json() cast leaked 'never' back into a later access.

frontend/src/editor/Canvas.tsx

@@ -4,6 +4,8 @@ import {
   useReactFlow, type Connection, type Edge, type Node, type NodeChange, type EdgeChange,
   applyNodeChanges, applyEdgeChanges,
 } from "@xyflow/react";
+
+const DELETE_KEYS = ["Delete", "Backspace"];
 import { nodeTypes as vcNodeTypes } from "./customNode";
 import type { VcNodeData } from "./graphAdapter";
 
@@ -51,6 +53,14 @@ function Inner({
         onEdgesChange={handleEdges}
         onConnect={onConnect}
         onSelectionChange={({ nodes: sel }) => onSelectNode(sel[0]?.id ?? null)}
+        onNodesDelete={(deleted) => {
+          // React Flow removes the nodes via applyNodeChanges above; it does
+          // NOT auto-remove edges whose endpoints just vanished. Filter here
+          // so the graph stays valid.
+          const gone = new Set(deleted.map((n) => n.id));
+          onEdgesChange(edges.filter((e) => !gone.has(e.source) && !gone.has(e.target)));
+        }}
+        deleteKeyCode={DELETE_KEYS}
         nodeTypes={vcNodeTypes}
         fitView
       >

frontend/src/pages/ConnectionsPage.test.tsx

@@ -38,9 +38,10 @@ describe("ConnectionsPage", () => {
           { id: "c1", providerId: "nats", name: "local", config: { url: "nats://old" } },
         ] as never)),
       http.put("/api/connections/c1", async ({ request }) => {
-        latestPut = await request.json() as never;
+        const body = await request.json() as { name?: string; config?: { url?: string; pass?: string } };
+        latestPut = body;
         return HttpResponse.json({
-          id: "c1", providerId: "nats", name: latestPut!.name, config: { url: latestPut!.config?.url },
+          id: "c1", providerId: "nats", name: body.name, config: { url: body.config?.url },
         } as never);
       }),
     );