fix(graph): resolve multi-node selection bug by enforcing unique concept IDs and hardening JS logic

src/NexusReader.Infrastructure/Services/PromptRegistry.cs

@@ -17,7 +17,8 @@ public static class PromptRegistry
         "You are an expert at information architecture. Extract key concepts and their relationships from the text to build a knowledge graph. " +
         "CRITICAL: Restrict 'label' to a maximum of 3 words. " +
         "CRITICAL: Extract a MAXIMUM of 15 key concepts/plot points and their relationships. " +
-        "CRITICAL: Each paragraph in the user text starts with [ID: some-id]. You MUST use these exact IDs as the 'id' for the nodes representing those blocks. " +
+        "CRITICAL: Each paragraph in the user text starts with [ID: some-id]. Use these IDs ONLY for nodes representing the blocks. " +
+        "CRITICAL: All other extracted 'concept' nodes MUST have unique, slug-style IDs based on their labels (e.g., 'dependency-injection'). " +
         "Include a 'current' node representing the block content itself if applicable. " +
         "CRITICAL: Limit the result to a MAXIMUM of 15 most relevant connections. " +
         "Return ONLY minified JSON. Schema: { \"graph\": { \"nodes\": [ { \"id\": \"string\", \"label\": \"string\", \"group\": \"concept|current\" } ], \"links\": [ { \"source\": \"string\", \"target\": \"string\", \"value\": 1 } ] } }";

src/NexusReader.UI.Shared/wwwroot/js/knowledgeGraph.js

@@ -247,6 +247,7 @@ function drag(simulation) {
 export function setActiveNode(nodeId) {
     if (!svgElement || !node) return;
     
+    // Safety check: ensure we only target the first occurrence if IDs are duplicated
     const targetNode = node.filter(d => d.id === nodeId);
     if (targetNode.empty()) {
         dimNodes(null);
@@ -254,20 +255,21 @@ export function setActiveNode(nodeId) {
         return;
     }
 
-    const d = targetNode.datum();
+    const firstMatch = targetNode.filter((d, i) => i === 0);
+    const d = firstMatch.datum();
     
     // Reset all active classes
     rootGroup.selectAll(".node-pill").classed("nexus-node-active", false);
-    targetNode.select(".node-pill").classed("nexus-node-active", true);
+    firstMatch.select(".node-pill").classed("nexus-node-active", true);
 
     // Position badge
     badge.style("display", "block").datum(d);
     badge.attr("transform", `translate(${d.x},${d.y})`);
 
-    // Dim others
+    // Dim others (only exact matches for nodeId will be fully opaque)
     dimNodes(nodeId);
 
-    // Smooth transition
+    // Smooth transition to the first matching node
     svgElement.transition().duration(1000).call(
         zoomBehavior.transform,
         d3.zoomIdentity.translate(width / 2, height / 2).scale(1.2).translate(-d.x, -d.y)